diff --git a/card-functionality/src/cards.rs b/card-functionality/src/cards.rs
index 489a79d..198d2b3 100644
--- a/card-functionality/src/cards.rs
+++ b/card-functionality/src/cards.rs
@@ -8,7 +8,7 @@ use anyhow::Result;
 use serde_derive::Deserialize;
 use std::collections::BTreeMap;
 
-use openpgp_card::CardApp;
+use openpgp_card::CardClient;
 use openpgp_card_pcsc::PcscClient;
 use openpgp_card_scdc::ScdClient;
 
@@ -38,7 +38,9 @@ pub struct TestCardApp {
 }
 
 impl TestCardApp {
-    pub(crate) fn get_card_app(&self) -> Result<CardApp> {
+    pub(crate) fn get_card_client(
+        &self,
+    ) -> Result<Box<dyn CardClient + Send + Sync>> {
         self.tc.open()
     }
 
@@ -89,7 +91,7 @@ pub enum TestCard {
 }
 
 impl TestCard {
-    pub fn open(&self) -> Result<CardApp> {
+    pub fn open(&self) -> Result<Box<dyn CardClient + Send + Sync>> {
         match self {
             Self::Pcsc(ident) => {
                 // Attempt to shutdown SCD, if it is running.
@@ -97,11 +99,11 @@ impl TestCard {
                 let res = ScdClient::shutdown_scd(None);
                 log::trace!(" Attempt to shutdown scd: {:?}", res);
 
-                Ok(PcscClient::open_by_ident(ident)?)
+                Ok(Box::new(PcscClient::open_by_ident(ident)?))
             }
             Self::Scdc(serial) => {
                 // println!("open scdc card {}", serial);
-                Ok(ScdClient::open_by_serial(None, serial)?)
+                Ok(Box::new(ScdClient::open_by_serial(None, serial)?))
             }
         }
     }
diff --git a/card-functionality/src/tests.rs b/card-functionality/src/tests.rs
index c927a75..9e5ee12 100644
--- a/card-functionality/src/tests.rs
+++ b/card-functionality/src/tests.rs
@@ -15,7 +15,7 @@ use sequoia_openpgp::Cert;
 use openpgp_card;
 use openpgp_card::algorithm::AlgoSimple;
 use openpgp_card::card_do::{KeyGenerationTime, Sex};
-use openpgp_card::{CardApp, Error, KeyType, StatusBytes};
+use openpgp_card::{CardApp, CardClient, Error, KeyType, StatusBytes};
 use openpgp_card_sequoia::card::Open;
 use openpgp_card_sequoia::util::{
     make_cert, public_key_material_to_key, public_to_fingerprint,
@@ -53,7 +53,7 @@ pub enum TestError {
 
 /// Run after each "upload keys", if key *was* uploaded (?)
 pub fn test_decrypt(
-    mut ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     param: &[&str],
 ) -> Result<TestOutput, TestError> {
     assert_eq!(
@@ -65,12 +65,12 @@ pub fn test_decrypt(
     let cert = Cert::from_str(param[0])?;
     let msg = param[1].to_string();
 
-    ca.verify_pw1("123456")?;
+    CardApp::verify_pw1(card_client, "123456")?;
 
     let p = StandardPolicy::new();
 
     let res = openpgp_card_sequoia::util::decrypt(
-        &mut ca,
+        card_client,
         &cert,
         msg.into_bytes(),
         &p,
@@ -84,18 +84,21 @@ pub fn test_decrypt(
 
 /// Run after each "upload keys", if key *was* uploaded (?)
 pub fn test_sign(
-    mut ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     param: &[&str],
 ) -> Result<TestOutput, TestError> {
     assert_eq!(param.len(), 1, "test_sign needs a filename for 'cert'");
 
-    ca.verify_pw1_for_signing("123456")?;
+    CardApp::verify_pw1_for_signing(card_client, "123456")?;
 
     let cert = Cert::from_str(param[0])?;
 
     let msg = "Hello world, I am signed.";
-    let sig =
-        openpgp_card_sequoia::util::sign(&mut ca, &cert, &mut msg.as_bytes())?;
+    let sig = openpgp_card_sequoia::util::sign(
+        card_client,
+        &cert,
+        &mut msg.as_bytes(),
+    )?;
 
     // validate sig
     assert!(util::verify_sig(&cert, msg.as_bytes(), sig.as_bytes())?);
@@ -104,10 +107,10 @@ pub fn test_sign(
 }
 
 fn check_key_upload_metadata(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     meta: &[(String, KeyGenerationTime)],
 ) -> Result<()> {
-    let ard = ca.application_related_data()?;
+    let ard = CardApp::application_related_data(card_client)?;
 
     // check fingerprints
     let card_fp = ard.fingerprints()?;
@@ -148,10 +151,10 @@ fn check_key_upload_algo_attrs() -> Result<()> {
 }
 
 pub fn test_print_caps(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
-    let ard = ca.application_related_data()?;
+    let ard = CardApp::application_related_data(card_client)?;
 
     let aid = ard.application_id()?;
     println!("aid: {:#x?}", aid);
@@ -169,17 +172,17 @@ pub fn test_print_caps(
 }
 
 pub fn test_print_algo_info(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
-    let ard = ca.application_related_data()?;
+    let ard = CardApp::application_related_data(card_client)?;
 
     let dec = ard.algorithm_attributes(KeyType::Decryption)?;
     println!("Current algorithm for the decrypt slot: {}", dec);
 
     println!();
 
-    let algo = ca.algorithm_information();
+    let algo = CardApp::algorithm_information(card_client);
     if let Ok(Some(algo)) = algo {
         println!("Card algorithm list:\n{}", algo);
     }
@@ -188,7 +191,7 @@ pub fn test_print_algo_info(
 }
 
 pub fn test_upload_keys(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     param: &[&str],
 ) -> Result<TestOutput, TestError> {
     assert_eq!(
@@ -197,16 +200,16 @@ pub fn test_upload_keys(
         "test_upload_keys needs a filename for 'cert'"
     );
 
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
     let cert = Cert::from_file(param[0])?;
 
     let p = StandardPolicy::new();
 
-    let meta = util::upload_subkeys(ca, &cert, &p)
+    let meta = util::upload_subkeys(card_client, &cert, &p)
         .map_err(|e| TestError::KeyUploadError(param[0].to_string(), e))?;
 
-    check_key_upload_metadata(ca, &meta)?;
+    check_key_upload_metadata(card_client, &meta)?;
 
     // FIXME: implement
     check_key_upload_algo_attrs()?;
@@ -216,10 +219,10 @@ pub fn test_upload_keys(
 
 /// Generate keys for each of the three KeyTypes
 pub fn test_keygen(
-    mut ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     param: &[&str],
 ) -> Result<TestOutput, TestError> {
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
     // Generate all three subkeys on card
     let algo = param[0];
@@ -227,12 +230,17 @@ pub fn test_keygen(
     let alg = AlgoSimple::try_from(algo)?;
 
     println!(" Generate subkey for Signing");
-    let (pkm, ts) =
-        ca.generate_key_simple(public_to_fingerprint, KeyType::Signing, alg)?;
+    let (pkm, ts) = CardApp::generate_key_simple(
+        card_client,
+        public_to_fingerprint,
+        KeyType::Signing,
+        alg,
+    )?;
     let key_sig = public_key_material_to_key(&pkm, KeyType::Signing, ts)?;
 
     println!(" Generate subkey for Decryption");
-    let (pkm, ts) = ca.generate_key_simple(
+    let (pkm, ts) = CardApp::generate_key_simple(
+        card_client,
         public_to_fingerprint,
         KeyType::Decryption,
         alg,
@@ -240,7 +248,8 @@ pub fn test_keygen(
     let key_dec = public_key_material_to_key(&pkm, KeyType::Decryption, ts)?;
 
     println!(" Generate subkey for Authentication");
-    let (pkm, ts) = ca.generate_key_simple(
+    let (pkm, ts) = CardApp::generate_key_simple(
+        card_client,
         public_to_fingerprint,
         KeyType::Authentication,
         alg,
@@ -249,7 +258,7 @@ pub fn test_keygen(
         public_key_material_to_key(&pkm, KeyType::Authentication, ts)?;
 
     // Generate a Cert for this set of generated keys
-    let mut open = Open::new(&mut ca)?;
+    let mut open = Open::new(card_client)?;
     let cert = make_cert(
         &mut open,
         key_sig,
@@ -267,15 +276,15 @@ pub fn test_keygen(
 
 /// Construct public key based on data from the card
 pub fn test_get_pub(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
-    let ard = ca.application_related_data()?;
+    let ard = CardApp::application_related_data(card_client)?;
     let key_gen = ard.key_generation_times()?;
 
     // --
 
-    let sig = ca.public_key(KeyType::Signing)?;
+    let sig = CardApp::public_key(card_client, KeyType::Signing)?;
     let ts = key_gen.signature().unwrap().get().into();
     let key = public_key_material_to_key(&sig, KeyType::Signing, ts)?;
 
@@ -283,7 +292,7 @@ pub fn test_get_pub(
 
     // --
 
-    let dec = ca.public_key(KeyType::Decryption)?;
+    let dec = CardApp::public_key(card_client, KeyType::Decryption)?;
     let ts = key_gen.decryption().unwrap().get().into();
     let key = public_key_material_to_key(&dec, KeyType::Decryption, ts)?;
 
@@ -291,7 +300,7 @@ pub fn test_get_pub(
 
     // --
 
-    let auth = ca.public_key(KeyType::Authentication)?;
+    let auth = CardApp::public_key(card_client, KeyType::Authentication)?;
     let ts = key_gen.authentication().unwrap().get().into();
     let key = public_key_material_to_key(&auth, KeyType::Authentication, ts)?;
 
@@ -306,10 +315,10 @@ pub fn test_get_pub(
 }
 
 pub fn test_reset(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
-    let _res = ca.factory_reset()?;
+    let _res = CardApp::factory_reset(card_client)?;
     Ok(vec![])
 }
 
@@ -319,25 +328,25 @@ pub fn test_reset(
 /// Returns an empty TestOutput, throws errors for unexpected Status codes
 /// and for unequal field values.
 pub fn test_set_user_data(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
     // name
-    ca.set_name("Bar<<Foo")?;
+    CardApp::set_name(card_client, "Bar<<Foo")?;
 
     // lang
-    ca.set_lang("deen")?;
+    CardApp::set_lang(card_client, "deen")?;
 
     // sex
-    ca.set_sex(Sex::Female)?;
+    CardApp::set_sex(card_client, Sex::Female)?;
 
     // url
-    ca.set_url("https://duckduckgo.com/")?;
+    CardApp::set_url(card_client, "https://duckduckgo.com/")?;
 
     // read all the fields back again, expect equal data
-    let ch = ca.cardholder_related_data()?;
+    let ch = CardApp::cardholder_related_data(card_client)?;
 
     assert_eq!(ch.name(), Some("Bar<<Foo"));
     assert_eq!(
@@ -346,54 +355,70 @@ pub fn test_set_user_data(
     );
     assert_eq!(ch.sex(), Some(Sex::Female));
 
-    let url = ca.url()?;
+    let url = CardApp::url(card_client)?;
     assert_eq!(url, "https://duckduckgo.com/".to_string());
 
     Ok(vec![])
 }
 
 pub fn test_private_data(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
     let out = vec![];
 
     println!();
 
-    let d = ca.private_use_do(1)?;
+    let d = CardApp::private_use_do(card_client, 1)?;
     println!("data 1 {:?}", d);
 
-    ca.verify_pw1("123456")?;
+    CardApp::verify_pw1(card_client, "123456")?;
 
-    ca.set_private_use_do(1, "Foo bar1!".as_bytes().to_vec())?;
-    ca.set_private_use_do(3, "Foo bar3!".as_bytes().to_vec())?;
+    CardApp::set_private_use_do(
+        card_client,
+        1,
+        "Foo bar1!".as_bytes().to_vec(),
+    )?;
+    CardApp::set_private_use_do(
+        card_client,
+        3,
+        "Foo bar3!".as_bytes().to_vec(),
+    )?;
 
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
-    ca.set_private_use_do(2, "Foo bar2!".as_bytes().to_vec())?;
-    ca.set_private_use_do(4, "Foo bar4!".as_bytes().to_vec())?;
+    CardApp::set_private_use_do(
+        card_client,
+        2,
+        "Foo bar2!".as_bytes().to_vec(),
+    )?;
+    CardApp::set_private_use_do(
+        card_client,
+        4,
+        "Foo bar4!".as_bytes().to_vec(),
+    )?;
 
-    let d = ca.private_use_do(1)?;
+    let d = CardApp::private_use_do(card_client, 1)?;
     println!("data 1 {:?}", d);
-    let d = ca.private_use_do(2)?;
+    let d = CardApp::private_use_do(card_client, 2)?;
     println!("data 2 {:?}", d);
-    let d = ca.private_use_do(3)?;
+    let d = CardApp::private_use_do(card_client, 3)?;
     println!("data 3 {:?}", d);
-    let d = ca.private_use_do(4)?;
+    let d = CardApp::private_use_do(card_client, 4)?;
     println!("data 4 {:?}", d);
 
     Ok(out)
 }
 
 pub fn test_cardholder_cert(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
     let mut out = vec![];
 
     println!();
 
-    match ca.cardholder_certificate() {
+    match CardApp::cardholder_certificate(card_client) {
         Ok(res) => {
             out.push(TestResult::Text(format!("got cert {:x?}", res.data())))
         }
@@ -406,11 +431,11 @@ pub fn test_cardholder_cert(
         }
     };
 
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
     let data = "Foo bar baz!".as_bytes();
 
-    match ca.set_cardholder_certificate(data.to_vec()) {
+    match CardApp::set_cardholder_certificate(card_client, data.to_vec()) {
         Ok(_resp) => out.push(TestResult::Text("set cert ok".to_string())),
         Err(e) => {
             out.push(TestResult::Text(format!(
@@ -421,7 +446,7 @@ pub fn test_cardholder_cert(
         }
     }
 
-    let res = ca.cardholder_certificate()?;
+    let res = CardApp::cardholder_certificate(card_client)?;
     out.push(TestResult::Text("get cert ok".to_string()));
 
     if res.data() != data {
@@ -434,7 +459,7 @@ pub fn test_cardholder_cert(
 
     // try using slot 2
 
-    match ca.select_data(2, &[0x7F, 0x21]) {
+    match CardApp::select_data(card_client, 2, &[0x7F, 0x21]) {
         Ok(_res) => out.push(TestResult::Text("select_data ok".to_string())),
         Err(e) => {
             out.push(TestResult::Text(format!("select_data: {:?}", e)));
@@ -446,24 +471,24 @@ pub fn test_cardholder_cert(
 }
 
 pub fn test_pw_status(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
     let out = vec![];
 
-    let ard = ca.application_related_data()?;
+    let ard = CardApp::application_related_data(card_client)?;
     let mut pws = ard.pw_status_bytes()?;
 
     println!("pws {:?}", pws);
 
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
     pws.set_pw1_cds_valid_once(false);
     pws.set_pw1_pin_block(true);
 
-    ca.set_pw_status_bytes(&pws, false)?;
+    CardApp::set_pw_status_bytes(card_client, &pws, false)?;
 
-    let ard = ca.application_related_data()?;
+    let ard = CardApp::application_related_data(card_client)?;
     let pws = ard.pw_status_bytes()?;
     println!("pws {:?}", pws);
 
@@ -474,7 +499,7 @@ pub fn test_pw_status(
 /// - verify pw3 (check) -> Status
 /// - verify pw1 (check) -> Status
 pub fn test_verify(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
     // Steps:
@@ -492,7 +517,7 @@ pub fn test_verify(
     let mut out = vec![];
 
     // try to set name without verify, assert result is not ok!
-    let res = ca.set_name("Notverified<<Hello");
+    let res = CardApp::set_name(card_client, "Notverified<<Hello");
 
     if let Err(Error::CardStatus(s)) = res {
         assert_eq!(s, StatusBytes::SecurityStatusNotSatisfied);
@@ -500,9 +525,9 @@ pub fn test_verify(
         panic!("Status should be 'SecurityStatusNotSatisfied'");
     }
 
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
-    match ca.check_pw3() {
+    match CardApp::check_pw3(card_client) {
         Err(Error::CardStatus(s)) => {
             // e.g. yubikey5 returns an error status!
             out.push(TestResult::Status(s));
@@ -513,14 +538,14 @@ pub fn test_verify(
         Ok(_) => out.push(TestResult::StatusOk),
     }
 
-    ca.set_name("Admin<<Hello")?;
+    CardApp::set_name(card_client, "Admin<<Hello")?;
 
-    let cardholder = ca.cardholder_related_data()?;
+    let cardholder = CardApp::cardholder_related_data(card_client)?;
     assert_eq!(cardholder.name(), Some("Admin<<Hello"));
 
-    ca.verify_pw1("123456")?;
+    CardApp::verify_pw1(card_client, "123456")?;
 
-    match ca.check_pw3() {
+    match CardApp::check_pw3(card_client) {
         Err(Error::CardStatus(s)) => {
             // e.g. yubikey5 returns an error status!
             out.push(TestResult::Status(s));
@@ -531,16 +556,16 @@ pub fn test_verify(
         Ok(_) => out.push(TestResult::StatusOk),
     }
 
-    ca.set_name("There<<Hello")?;
+    CardApp::set_name(card_client, "There<<Hello")?;
 
-    let cardholder = ca.cardholder_related_data()?;
+    let cardholder = CardApp::cardholder_related_data(card_client)?;
     assert_eq!(cardholder.name(), Some("There<<Hello"));
 
     Ok(out)
 }
 
 pub fn test_change_pw(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
     let out = vec![];
@@ -548,20 +573,20 @@ pub fn test_change_pw(
     // first do admin-less pw1 on gnuk
     // (NOTE: Gnuk requires a key to be loaded before allowing pw changes!)
     println!("change pw1");
-    ca.change_pw1("123456", "abcdef00")?;
+    CardApp::change_pw1(card_client, "123456", "abcdef00")?;
 
     // also set admin pw, which means pw1 is now only user-pw again, on gnuk
     println!("change pw3");
     // ca.change_pw3("abcdef00", "abcdefgh")?; // gnuk
-    ca.change_pw3("12345678", "abcdefgh")?;
+    CardApp::change_pw3(card_client, "12345678", "abcdefgh")?;
 
     println!("change pw1");
-    ca.change_pw1("abcdef00", "abcdef")?; // gnuk
+    CardApp::change_pw1(card_client, "abcdef00", "abcdef")?; // gnuk
 
     // ca.change_pw1("123456", "abcdef")?;
 
     println!("verify bad pw1");
-    match ca.verify_pw1("123456ab") {
+    match CardApp::verify_pw1(card_client, "123456ab") {
         Err(Error::CardStatus(StatusBytes::SecurityStatusNotSatisfied)) => {
             // this is expected
         }
@@ -572,10 +597,10 @@ pub fn test_change_pw(
     }
 
     println!("verify good pw1");
-    ca.verify_pw1("abcdef")?;
+    CardApp::verify_pw1(card_client, "abcdef")?;
 
     println!("verify bad pw3");
-    match ca.verify_pw3("00000000") {
+    match CardApp::verify_pw3(card_client, "00000000") {
         Err(Error::CardStatus(StatusBytes::SecurityStatusNotSatisfied)) => {
             // this is expected
         }
@@ -586,34 +611,34 @@ pub fn test_change_pw(
     }
 
     println!("verify good pw3");
-    ca.verify_pw3("abcdefgh")?;
+    CardApp::verify_pw3(card_client, "abcdefgh")?;
 
     println!("change pw3 back to default");
-    ca.change_pw3("abcdefgh", "12345678")?;
+    CardApp::change_pw3(card_client, "abcdefgh", "12345678")?;
 
     println!("change pw1 back to default");
-    ca.change_pw1("abcdef", "123456")?;
+    CardApp::change_pw1(card_client, "abcdef", "123456")?;
 
     Ok(out)
 }
 
 pub fn test_reset_retry_counter(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     _param: &[&str],
 ) -> Result<TestOutput, TestError> {
     let out = vec![];
 
     // set pw3, then pw1 (to bring gnuk into non-admin mode)
     println!("set pw3");
-    ca.change_pw3("12345678", "12345678")?;
+    CardApp::change_pw3(card_client, "12345678", "12345678")?;
     println!("set pw1");
-    ca.change_pw1("123456", "123456")?;
+    CardApp::change_pw1(card_client, "123456", "123456")?;
 
     println!("break pw1");
-    let _ = ca.verify_pw1("wrong0");
-    let _ = ca.verify_pw1("wrong0");
-    let _ = ca.verify_pw1("wrong0");
-    let res = ca.verify_pw1("wrong0");
+    let _ = CardApp::verify_pw1(card_client, "wrong0");
+    let _ = CardApp::verify_pw1(card_client, "wrong0");
+    let _ = CardApp::verify_pw1(card_client, "wrong0");
+    let res = CardApp::verify_pw1(card_client, "wrong0");
 
     match res {
         Err(Error::CardStatus(StatusBytes::AuthenticationMethodBlocked)) => {
@@ -634,23 +659,24 @@ pub fn test_reset_retry_counter(
     }
 
     println!("verify pw3");
-    ca.verify_pw3("12345678")?;
+    CardApp::verify_pw3(card_client, "12345678")?;
 
     println!("set resetting code");
-    ca.set_resetting_code("abcdefgh".as_bytes().to_vec())?;
+    CardApp::set_resetting_code(card_client, "abcdefgh".as_bytes().to_vec())?;
 
     println!("reset retry counter");
     // ca.reset_retry_counter_pw1("abcdef".as_bytes().to_vec(), None)?;
-    let _res = ca.reset_retry_counter_pw1(
+    let _res = CardApp::reset_retry_counter_pw1(
+        card_client,
         "abcdef".as_bytes().to_vec(),
         Some("abcdefgh".as_bytes().to_vec()),
     );
 
     println!("verify good pw1");
-    ca.verify_pw1("abcdef")?;
+    CardApp::verify_pw1(card_client, "abcdef")?;
 
     println!("verify bad pw1");
-    match ca.verify_pw1("00000000") {
+    match CardApp::verify_pw1(card_client, "00000000") {
         Err(Error::CardStatus(StatusBytes::SecurityStatusNotSatisfied)) => {
             // this is expected
         }
@@ -665,12 +691,15 @@ pub fn test_reset_retry_counter(
 
 pub fn run_test(
     card: &mut TestCardApp,
-    t: fn(&mut CardApp, &[&str]) -> Result<TestOutput, TestError>,
+    t: fn(
+        &mut (dyn CardClient + Send + Sync),
+        &[&str],
+    ) -> Result<TestOutput, TestError>,
     param: &[&str],
 ) -> Result<TestOutput, TestError> {
-    let mut ca = card.get_card_app()?;
-    let ard = ca.application_related_data()?;
+    let mut card_client = card.get_card_client()?;
+    let ard = CardApp::application_related_data(&mut *card_client)?;
     let _app_id = ard.application_id()?;
 
-    t(&mut ca, param)
+    t(&mut *card_client, param)
 }
diff --git a/card-functionality/src/util.rs b/card-functionality/src/util.rs
index 4c1b2ac..0049910 100644
--- a/card-functionality/src/util.rs
+++ b/card-functionality/src/util.rs
@@ -17,14 +17,14 @@ use sequoia_openpgp::serialize::stream::{
 use sequoia_openpgp::Cert;
 
 use openpgp_card::card_do::KeyGenerationTime;
-use openpgp_card::{CardApp, KeyType};
+use openpgp_card::{CardApp, CardClient, KeyType};
 use openpgp_card_sequoia::sq_util;
 use openpgp_card_sequoia::util::vka_as_uploadable_key;
 
 pub const SP: &StandardPolicy = &StandardPolicy::new();
 
 pub(crate) fn upload_subkeys(
-    ca: &mut CardApp,
+    card_client: &mut dyn CardClient,
     cert: &Cert,
     policy: &dyn Policy,
 ) -> Result<Vec<(String, KeyGenerationTime)>> {
@@ -49,7 +49,7 @@ pub(crate) fn upload_subkeys(
 
             // upload key
             let cuk = vka_as_uploadable_key(vka, None);
-            ca.key_import(cuk, *kt)?;
+            CardApp::key_import(card_client, cuk, *kt)?;
         }
     }
 
diff --git a/openpgp-card-sequoia/src/card.rs b/openpgp-card-sequoia/src/card.rs
index adda8f4..cb11936 100644
--- a/openpgp-card-sequoia/src/card.rs
+++ b/openpgp-card-sequoia/src/card.rs
@@ -16,7 +16,7 @@ use openpgp_card::card_do::{
     ExtendedCapabilities, ExtendedLengthInfo, Fingerprint, HistoricalBytes,
     KeyGenerationTime, PWStatusBytes, SecuritySupportTemplate, Sex,
 };
-use openpgp_card::{CardApp, Error, KeySet, KeyType, Response};
+use openpgp_card::{CardApp, CardClient, Error, KeySet, KeyType, Response};
 
 use crate::decryptor::CardDecryptor;
 use crate::signer::CardSigner;
@@ -27,7 +27,7 @@ use openpgp_card::crypto_data::PublicKeyMaterial;
 /// Representation of an opened OpenPGP card in its base state (i.e. no
 /// passwords have been verified, default authorization applies).
 pub struct Open<'a> {
-    card_app: &'a mut CardApp,
+    card_client: &'a mut (dyn CardClient + Send + Sync),
 
     // Cache of "application related data".
     //
@@ -46,27 +46,29 @@ pub struct Open<'a> {
 }
 
 impl<'a> Open<'a> {
-    pub fn new(card_app: &'a mut CardApp) -> Result<Self, Error> {
-        let ard = card_app.application_related_data()?;
+    pub fn new(
+        card_client: &'a mut (dyn CardClient + Send + Sync),
+    ) -> Result<Self, Error> {
+        let ard = CardApp::application_related_data(card_client)?;
 
         Ok(Self {
-            card_app,
+            card_client,
             ard,
             pw1: false,
             pw1_sign: false,
             pw3: false,
         })
     }
-    pub fn feature_pinpad_verify(&self) -> bool {
-        self.card_app.feature_pinpad_verify()
+    pub fn feature_pinpad_verify(&mut self) -> bool {
+        CardApp::feature_pinpad_verify(self.card_client)
     }
 
-    pub fn feature_pinpad_modify(&self) -> bool {
-        self.card_app.feature_pinpad_modify()
+    pub fn feature_pinpad_modify(&mut self) -> bool {
+        CardApp::feature_pinpad_modify(self.card_client)
     }
 
     pub fn verify_user(&mut self, pin: &str) -> Result<(), Error> {
-        let _ = self.card_app.verify_pw1(pin)?;
+        let _ = CardApp::verify_pw1(self.card_client, pin)?;
         self.pw1 = true;
         Ok(())
     }
@@ -77,13 +79,13 @@ impl<'a> Open<'a> {
     ) -> Result<(), Error> {
         prompt();
 
-        let _ = self.card_app.verify_pw1_pinpad()?;
+        let _ = CardApp::verify_pw1_pinpad(self.card_client)?;
         self.pw1 = true;
         Ok(())
     }
 
     pub fn verify_user_for_signing(&mut self, pin: &str) -> Result<(), Error> {
-        let _ = self.card_app.verify_pw1_for_signing(pin)?;
+        let _ = CardApp::verify_pw1_for_signing(self.card_client, pin)?;
 
         // FIXME: depending on card mode, pw1_sign is only usable once
 
@@ -97,7 +99,7 @@ impl<'a> Open<'a> {
     ) -> Result<(), Error> {
         prompt();
 
-        let _ = self.card_app.verify_pw1_for_signing_pinpad()?;
+        let _ = CardApp::verify_pw1_for_signing_pinpad(self.card_client)?;
 
         // FIXME: depending on card mode, pw1_sign is only usable once
 
@@ -106,7 +108,7 @@ impl<'a> Open<'a> {
     }
 
     pub fn verify_admin(&mut self, pin: &str) -> Result<(), Error> {
-        let _ = self.card_app.verify_pw3(pin)?;
+        let _ = CardApp::verify_pw3(self.card_client, pin)?;
         self.pw3 = true;
         Ok(())
     }
@@ -117,7 +119,7 @@ impl<'a> Open<'a> {
     ) -> Result<(), Error> {
         prompt();
 
-        let _ = self.card_app.verify_pw3_pinpad()?;
+        let _ = CardApp::verify_pw3_pinpad(self.card_client)?;
         self.pw3 = true;
         Ok(())
     }
@@ -126,14 +128,14 @@ impl<'a> Open<'a> {
     ///
     /// NOTE: on some cards this functionality seems broken.
     pub fn check_user_verified(&mut self) -> Result<Response, Error> {
-        self.card_app.check_pw1()
+        CardApp::check_pw1(self.card_client)
     }
 
     /// Ask the card if the admin password has been successfully verified.
     ///
     /// NOTE: on some cards this functionality seems broken.
     pub fn check_admin_verified(&mut self) -> Result<Response, Error> {
-        self.card_app.check_pw3()
+        CardApp::check_pw3(self.card_client)
     }
 
     pub fn change_user_pin(
@@ -141,7 +143,7 @@ impl<'a> Open<'a> {
         old: &str,
         new: &str,
     ) -> Result<Response, Error> {
-        self.card_app.change_pw1(old, new)
+        CardApp::change_pw1(self.card_client, old, new)
     }
 
     pub fn change_user_pin_pinpad(
@@ -149,7 +151,7 @@ impl<'a> Open<'a> {
         prompt: &dyn Fn(),
     ) -> Result<Response, Error> {
         prompt();
-        self.card_app.change_pw1_pinpad()
+        CardApp::change_pw1_pinpad(self.card_client)
     }
 
     pub fn reset_user_pin(
@@ -157,8 +159,11 @@ impl<'a> Open<'a> {
         rst: &str,
         new: &str,
     ) -> Result<Response, Error> {
-        self.card_app
-            .reset_retry_counter_pw1(new.into(), Some(rst.into()))
+        CardApp::reset_retry_counter_pw1(
+            self.card_client,
+            new.into(),
+            Some(rst.into()),
+        )
     }
 
     pub fn change_admin_pin(
@@ -166,7 +171,7 @@ impl<'a> Open<'a> {
         old: &str,
         new: &str,
     ) -> Result<Response, Error> {
-        self.card_app.change_pw3(old, new)
+        CardApp::change_pw3(self.card_client, old, new)
     }
 
     pub fn change_admin_pin_pinpad(
@@ -174,7 +179,7 @@ impl<'a> Open<'a> {
         prompt: &dyn Fn(),
     ) -> Result<Response, Error> {
         prompt();
-        self.card_app.change_pw3_pinpad()
+        CardApp::change_pw3_pinpad(self.card_client)
     }
 
     /// Get a view of the card authenticated for "User" commands.
@@ -294,21 +299,21 @@ impl<'a> Open<'a> {
     // --- URL (5f50) ---
 
     pub fn url(&mut self) -> Result<String> {
-        self.card_app.url()
+        CardApp::url(self.card_client)
     }
 
     // --- cardholder related data (65) ---
     pub fn cardholder_related_data(
         &mut self,
     ) -> Result<CardholderRelatedData> {
-        self.card_app.cardholder_related_data()
+        CardApp::cardholder_related_data(self.card_client)
     }
 
     // --- security support template (7a) ---
     pub fn security_support_template(
         &mut self,
     ) -> Result<SecuritySupportTemplate> {
-        self.card_app.security_support_template()
+        CardApp::security_support_template(self.card_client)
     }
 
     // DO "Algorithm Information" (0xFA)
@@ -322,12 +327,12 @@ impl<'a> Open<'a> {
             return Ok(None);
         }
 
-        self.card_app.algorithm_information()
+        CardApp::algorithm_information(self.card_client)
     }
 
     /// Firmware Version, YubiKey specific (?)
     pub fn firmware_version(&mut self) -> Result<Vec<u8>> {
-        self.card_app.firmware_version()
+        CardApp::firmware_version(self.card_client)
     }
 
     // ----------
@@ -336,14 +341,14 @@ impl<'a> Open<'a> {
         &mut self,
         key_type: KeyType,
     ) -> Result<PublicKeyMaterial> {
-        self.card_app.public_key(key_type).map_err(|e| e.into())
+        CardApp::public_key(self.card_client, key_type).map_err(|e| e.into())
     }
 
     // ----------
 
     /// Delete all state on this OpenPGP card
     pub fn factory_reset(&mut self) -> Result<()> {
-        self.card_app.factory_reset()
+        CardApp::factory_reset(self.card_client)
     }
 }
 
@@ -355,7 +360,7 @@ pub struct User<'app, 'open> {
 
 impl User<'_, '_> {
     pub fn decryptor(&mut self, cert: &Cert) -> Result<CardDecryptor, Error> {
-        CardDecryptor::new(&mut self.oc.card_app, cert)
+        CardDecryptor::new(self.oc.card_client, cert)
     }
 }
 
@@ -373,14 +378,14 @@ impl Sign<'_, '_> {
         // FIXME: depending on the setting in "PW1 Status byte", only one
         // signature can be made after verification for signing
 
-        CardSigner::new(&mut self.oc.card_app, cert)
+        CardSigner::new(self.oc.card_client, cert)
     }
 
     pub fn signer_from_pubkey(&mut self, pubkey: PublicKey) -> CardSigner {
         // FIXME: depending on the setting in "PW1 Status byte", only one
         // signature can be made after verification for signing
 
-        CardSigner::with_pubkey(&mut self.oc.card_app, pubkey)
+        CardSigner::with_pubkey(self.oc.card_client, pubkey)
     }
 }
 
@@ -406,7 +411,7 @@ impl Admin<'_, '_> {
             return Err(anyhow!("Invalid char in name").into());
         };
 
-        self.oc.card_app.set_name(name)
+        CardApp::set_name(self.oc.card_client, name)
     }
 
     pub fn set_lang(&mut self, lang: &str) -> Result<Response, Error> {
@@ -414,11 +419,11 @@ impl Admin<'_, '_> {
             return Err(anyhow!("lang too long").into());
         }
 
-        self.oc.card_app.set_lang(lang)
+        CardApp::set_lang(self.oc.card_client, lang)
     }
 
     pub fn set_sex(&mut self, sex: Sex) -> Result<Response, Error> {
-        self.oc.card_app.set_sex(sex)
+        CardApp::set_sex(self.oc.card_client, sex)
     }
 
     pub fn set_url(&mut self, url: &str) -> Result<Response, Error> {
@@ -436,7 +441,7 @@ impl Admin<'_, '_> {
             // or if it's within the acceptable length:
             // send the url update to the card.
 
-            self.oc.card_app.set_url(url)
+            CardApp::set_url(self.oc.card_client, url)
         } else {
             Err(anyhow!("URL too long").into())
         }
@@ -446,11 +451,11 @@ impl Admin<'_, '_> {
         &mut self,
         pin: &str,
     ) -> Result<Response, Error> {
-        self.oc.card_app.set_resetting_code(pin.into())
+        CardApp::set_resetting_code(self.oc.card_client, pin.into())
     }
 
     pub fn reset_user_pin(&mut self, new: &str) -> Result<Response, Error> {
-        self.oc.card_app.reset_retry_counter_pw1(new.into(), None)
+        CardApp::reset_retry_counter_pw1(self.oc.card_client, new.into(), None)
     }
 
     /// Upload a ValidErasedKeyAmalgamation to the card as a specific KeyType.
@@ -463,7 +468,7 @@ impl Admin<'_, '_> {
         password: Option<String>,
     ) -> Result<(), Error> {
         let key = vka_as_uploadable_key(vka, password);
-        self.oc.card_app.key_import(key, key_type)
+        CardApp::key_import(self.oc.card_client, key, key_type)
     }
 
     pub fn generate_key_simple(
@@ -472,12 +477,14 @@ impl Admin<'_, '_> {
         algo: Option<AlgoSimple>,
     ) -> Result<(PublicKeyMaterial, KeyGenerationTime), Error> {
         match algo {
-            Some(algo) => self.oc.card_app.generate_key_simple(
+            Some(algo) => CardApp::generate_key_simple(
+                self.oc.card_client,
                 public_to_fingerprint,
                 key_type,
                 algo,
             ),
-            None => self.oc.card_app.generate_key(
+            None => CardApp::generate_key(
+                self.oc.card_client,
                 public_to_fingerprint,
                 key_type,
                 None,
diff --git a/openpgp-card-sequoia/src/decryptor.rs b/openpgp-card-sequoia/src/decryptor.rs
index 6a4f872..1ebcdbf 100644
--- a/openpgp-card-sequoia/src/decryptor.rs
+++ b/openpgp-card-sequoia/src/decryptor.rs
@@ -15,14 +15,14 @@ use openpgp::Cert;
 use sequoia_openpgp as openpgp;
 
 use openpgp_card::crypto_data::Cryptogram;
-use openpgp_card::{CardApp, Error};
+use openpgp_card::{CardApp, CardClient, Error};
 
 use crate::sq_util;
 use crate::PublicKey;
 
 pub struct CardDecryptor<'a> {
     /// The OpenPGP card (authenticated to allow decryption operations)
-    ca: &'a mut CardApp,
+    card_client: &'a mut dyn CardClient,
 
     /// The matching public key for the card's decryption key
     public: PublicKey,
@@ -34,11 +34,11 @@ impl<'a> CardDecryptor<'a> {
     /// An Error is returned if no match between the card's decryption
     /// key and a (sub)key of `cert` can be made.
     pub fn new(
-        ca: &'a mut CardApp,
+        card_client: &'a mut dyn CardClient,
         cert: &Cert,
     ) -> Result<CardDecryptor<'a>, Error> {
         // Get the fingerprint for the decryption key from the card.
-        let ard = ca.application_related_data()?;
+        let ard = CardApp::application_related_data(card_client)?;
         let fps = ard.fingerprints()?;
         let fp = fps.decryption();
 
@@ -48,7 +48,10 @@ impl<'a> CardDecryptor<'a> {
 
             if let Some(eka) = sq_util::get_subkey_by_fingerprint(cert, &fp)? {
                 let public = eka.key().clone();
-                Ok(Self { ca, public })
+                Ok(Self {
+                    card_client,
+                    public,
+                })
             } else {
                 Err(Error::InternalError(anyhow!(
                     "Failed to find (sub)key {} in cert",
@@ -82,7 +85,7 @@ impl<'a> crypto::Decryptor for CardDecryptor<'a> {
         match (ciphertext, self.public.mpis()) {
             (mpi::Ciphertext::RSA { c: ct }, mpi::PublicKey::RSA { .. }) => {
                 let dm = Cryptogram::RSA(ct.value());
-                let dec = self.ca.decipher(dm)?;
+                let dec = CardApp::decipher(self.card_client, dm)?;
 
                 let sk = openpgp::crypto::SessionKey::from(&dec[..]);
                 Ok(sk)
@@ -106,7 +109,7 @@ impl<'a> crypto::Decryptor for CardDecryptor<'a> {
                 };
 
                 // Decryption operation on the card
-                let mut dec = self.ca.decipher(dm)?;
+                let mut dec = CardApp::decipher(self.card_client, dm)?;
 
                 // Specifically handle return value format like Gnuk's
                 // (Gnuk returns a leading '0x04' byte and
diff --git a/openpgp-card-sequoia/src/signer.rs b/openpgp-card-sequoia/src/signer.rs
index bfda776..69c627f 100644
--- a/openpgp-card-sequoia/src/signer.rs
+++ b/openpgp-card-sequoia/src/signer.rs
@@ -11,14 +11,14 @@ use openpgp::types::{Curve, PublicKeyAlgorithm};
 use sequoia_openpgp as openpgp;
 
 use openpgp_card::crypto_data::Hash;
-use openpgp_card::{CardApp, Error};
+use openpgp_card::{CardApp, CardClient, Error};
 
 use crate::sq_util;
 use crate::PublicKey;
 
 pub struct CardSigner<'a> {
     /// The OpenPGP card (authenticated to allow signing operations)
-    ca: &'a mut CardApp,
+    card_client: &'a mut (dyn CardClient + Send + Sync),
 
     /// The matching public key for the card's signing key
     public: PublicKey,
@@ -30,11 +30,11 @@ impl<'a> CardSigner<'a> {
     /// An Error is returned if no match between the card's signing
     /// key and a (sub)key of `cert` can be made.
     pub fn new(
-        ca: &'a mut CardApp,
+        card_client: &'a mut (dyn CardClient + Send + Sync),
         cert: &openpgp::Cert,
     ) -> Result<CardSigner<'a>, Error> {
         // Get the fingerprint for the signing key from the card.
-        let ard = ca.application_related_data()?;
+        let ard = CardApp::application_related_data(card_client)?;
         let fps = ard.fingerprints()?;
         let fp = fps.signature();
 
@@ -44,7 +44,7 @@ impl<'a> CardSigner<'a> {
 
             if let Some(eka) = sq_util::get_subkey_by_fingerprint(cert, &fp)? {
                 let key = eka.key().clone();
-                Ok(Self::with_pubkey(ca, key))
+                Ok(Self::with_pubkey(card_client, key))
             } else {
                 Err(Error::InternalError(anyhow!(
                     "Failed to find (sub)key {} in cert",
@@ -59,10 +59,13 @@ impl<'a> CardSigner<'a> {
     }
 
     pub(crate) fn with_pubkey(
-        ca: &'a mut CardApp,
+        card_client: &'a mut (dyn CardClient + Send + Sync),
         public: PublicKey,
     ) -> CardSigner<'a> {
-        CardSigner { ca, public }
+        CardSigner {
+            card_client,
+            public,
+        }
     }
 }
 
@@ -114,7 +117,7 @@ impl<'a> crypto::Signer for CardSigner<'a> {
                     }
                 };
 
-                let sig = self.ca.signature_for_hash(hash)?;
+                let sig = CardApp::signature_for_hash(self.card_client, hash)?;
 
                 let mpi = mpi::MPI::new(&sig[..]);
                 Ok(mpi::Signature::RSA { s: mpi })
@@ -122,7 +125,7 @@ impl<'a> crypto::Signer for CardSigner<'a> {
             (PublicKeyAlgorithm::EdDSA, mpi::PublicKey::EdDSA { .. }) => {
                 let hash = Hash::EdDSA(digest);
 
-                let sig = self.ca.signature_for_hash(hash)?;
+                let sig = CardApp::signature_for_hash(self.card_client, hash)?;
 
                 let r = mpi::MPI::new(&sig[..32]);
                 let s = mpi::MPI::new(&sig[32..]);
@@ -140,7 +143,7 @@ impl<'a> crypto::Signer for CardSigner<'a> {
                     _ => Hash::ECDSA(digest),
                 };
 
-                let sig = self.ca.signature_for_hash(hash)?;
+                let sig = CardApp::signature_for_hash(self.card_client, hash)?;
 
                 let len_2 = sig.len() / 2;
                 let r = mpi::MPI::new(&sig[..len_2]);
diff --git a/openpgp-card-sequoia/src/util.rs b/openpgp-card-sequoia/src/util.rs
index e00163d..3623512 100644
--- a/openpgp-card-sequoia/src/util.rs
+++ b/openpgp-card-sequoia/src/util.rs
@@ -27,7 +27,7 @@ use sequoia_openpgp as openpgp;
 use openpgp_card::algorithm::{Algo, Curve};
 use openpgp_card::card_do::{Fingerprint, KeyGenerationTime};
 use openpgp_card::crypto_data::{CardUploadableKey, PublicKeyMaterial};
-use openpgp_card::{CardApp, Error, KeyType};
+use openpgp_card::{CardClient, Error, KeyType};
 
 use crate::card::Open;
 use crate::privkey::SequoiaKey;
@@ -294,13 +294,13 @@ pub fn vka_as_uploadable_key(
 
 /// FIXME: this fn is used in card_functionality, but should be removed
 pub fn sign(
-    ca: &mut CardApp,
+    card_client: &mut (dyn CardClient + Send + Sync),
     cert: &Cert,
     input: &mut dyn io::Read,
 ) -> Result<String> {
     let mut armorer = armor::Writer::new(vec![], armor::Kind::Signature)?;
     {
-        let s = signer::CardSigner::new(ca, cert)?;
+        let s = signer::CardSigner::new(card_client, cert)?;
 
         let message = Message::new(&mut armorer);
         let mut message = Signer::new(message, s).detached().build()?;
@@ -318,7 +318,7 @@ pub fn sign(
 
 /// FIXME: this fn is used in card_functionality, but should be removed
 pub fn decrypt(
-    ca: &mut CardApp,
+    card_client: &mut dyn CardClient,
     cert: &Cert,
     msg: Vec<u8>,
     p: &dyn Policy,
@@ -327,7 +327,7 @@ pub fn decrypt(
     {
         let reader = io::BufReader::new(&msg[..]);
 
-        let d = decryptor::CardDecryptor::new(ca, cert)?;
+        let d = decryptor::CardDecryptor::new(card_client, cert)?;
 
         let db = DecryptorBuilder::from_reader(reader)?;
         let mut decryptor = db.with_policy(p, None, d)?;
diff --git a/openpgp-card/src/card_app.rs b/openpgp-card/src/card_app.rs
index a71b734..d7eba3a 100644
--- a/openpgp-card/src/card_app.rs
+++ b/openpgp-card/src/card_app.rs
@@ -19,9 +19,7 @@ use crate::crypto_data::{
     CardUploadableKey, Cryptogram, Hash, PublicKeyMaterial,
 };
 use crate::tlv::{tag::Tag, value::Value, Tlv};
-use crate::{
-    apdu, keys, CardCaps, CardClient, CardClientBox, KeyType, SmartcardError,
-};
+use crate::{apdu, keys, CardCaps, CardClient, KeyType, SmartcardError};
 use crate::{Error, StatusBytes};
 
 /// Low-level access to OpenPGP card functionality.
@@ -31,9 +29,7 @@ use crate::{Error, StatusBytes};
 ///
 /// Also, no caching of data is done here. If necessary, caching should
 /// be done on a higher layer.
-pub struct CardApp {
-    card_client: CardClientBox,
-}
+pub struct CardApp {}
 
 impl CardApp {
     /// Get a CardApp based on a CardClient.
@@ -44,25 +40,21 @@ impl CardApp {
     /// This fn initializes the CardCaps by requesting
     /// application_related_data from the card, and setting the
     /// capabilities accordingly.
-    pub fn initialize(card_client: CardClientBox) -> Result<Self> {
-        let mut ca = Self { card_client };
+    pub fn initialize(card_client: &mut dyn CardClient) -> Result<()> {
+        let ard = Self::application_related_data(card_client)?;
+        Self::init_caps(card_client, &ard)?;
 
-        let ard = ca.application_related_data()?;
-        ca.init_caps(&ard)?;
-
-        Ok(ca)
-    }
-
-    /// Get the CardClient of this CardApp
-    pub(crate) fn card_client(&mut self) -> &mut dyn CardClient {
-        &mut *self.card_client
+        Ok(())
     }
 
     /// Initialize the CardCaps settings in the underlying CardClient
     /// from the data in `ard`.
     ///
     /// This should be done at an early point, soon after opening the card.
-    fn init_caps(&mut self, ard: &ApplicationRelatedData) -> Result<()> {
+    fn init_caps(
+        card_client: &mut dyn CardClient,
+        ard: &ApplicationRelatedData,
+    ) -> Result<()> {
         // Determine chaining/extended length support from card
         // metadata and cache this information in CardApp (as a
         // CardCaps)
@@ -107,7 +99,9 @@ impl CardApp {
             pw3_max_len: pw3_max,
         };
 
-        self.card_client.init_card_caps(caps);
+        log::debug!("init_card_caps to: {:x?}", caps);
+
+        card_client.init_card_caps(caps);
 
         Ok(())
     }
@@ -120,10 +114,10 @@ impl CardApp {
     /// it are needed regularly, and it does not usually change during
     /// normal use of a card.)
     pub fn application_related_data(
-        &mut self,
+        card_client: &mut dyn CardClient,
     ) -> Result<ApplicationRelatedData> {
         let ad = commands::application_related_data();
-        let resp = apdu::send_command(self.card_client(), ad, true)?;
+        let resp = apdu::send_command(card_client, ad, true)?;
         let value = Value::from(resp.data()?, true)?;
 
         log::debug!(" App data Value: {:x?}", value);
@@ -164,19 +158,18 @@ impl CardApp {
     // --- login data (5e) ---
 
     /// Get URL (5f50)
-    pub fn url(&mut self) -> Result<String> {
-        let resp =
-            apdu::send_command(self.card_client(), commands::url(), true)?;
+    pub fn url(card_client: &mut dyn CardClient) -> Result<String> {
+        let resp = apdu::send_command(card_client, commands::url(), true)?;
 
         Ok(String::from_utf8_lossy(resp.data()?).to_string())
     }
 
     /// Get cardholder related data (65)
     pub fn cardholder_related_data(
-        &mut self,
+        card_client: &mut dyn CardClient,
     ) -> Result<CardholderRelatedData> {
         let crd = commands::cardholder_related_data();
-        let resp = apdu::send_command(self.card_client(), crd, true)?;
+        let resp = apdu::send_command(card_client, crd, true)?;
         resp.check_ok()?;
 
         CardholderRelatedData::try_from(resp.data()?)
@@ -184,10 +177,10 @@ impl CardApp {
 
     /// Get security support template (7a)
     pub fn security_support_template(
-        &mut self,
+        card_client: &mut dyn CardClient,
     ) -> Result<SecuritySupportTemplate> {
         let sst = commands::security_support_template();
-        let resp = apdu::send_command(self.card_client(), sst, true)?;
+        let resp = apdu::send_command(card_client, sst, true)?;
         resp.check_ok()?;
 
         let tlv = Tlv::try_from(resp.data()?)?;
@@ -213,18 +206,19 @@ impl CardApp {
     ///
     /// Call select_data() before calling this fn, to select a particular
     /// certificate (if the card supports multiple certificates).
-    pub fn cardholder_certificate(&mut self) -> Result<Response, Error> {
+    pub fn cardholder_certificate(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
         let cmd = commands::cardholder_certificate();
-        apdu::send_command(self.card_client(), cmd, true)?.try_into()
+        apdu::send_command(card_client, cmd, true)?.try_into()
     }
 
     /// Get "Algorithm Information"
-    pub fn algorithm_information(&mut self) -> Result<Option<AlgoInfo>> {
-        let resp = apdu::send_command(
-            self.card_client(),
-            commands::algo_info(),
-            true,
-        )?;
+    pub fn algorithm_information(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Option<AlgoInfo>> {
+        let resp =
+            apdu::send_command(card_client, commands::algo_info(), true)?;
         resp.check_ok()?;
 
         let ai = AlgoInfo::try_from(resp.data()?)?;
@@ -232,9 +226,11 @@ impl CardApp {
     }
 
     /// Firmware Version (YubiKey specific (?))
-    pub fn firmware_version(&mut self) -> Result<Vec<u8>> {
+    pub fn firmware_version(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Vec<u8>> {
         let resp = apdu::send_command(
-            self.card_client(),
+            card_client,
             commands::firmware_version(),
             true,
         )?;
@@ -246,12 +242,12 @@ impl CardApp {
     /// [see:
     /// <https://docs.nitrokey.com/start/linux/multiple-identities.html>
     /// <https://github.com/Nitrokey/nitrokey-start-firmware/pull/33/>]
-    pub fn set_identity(&mut self, id: u8) -> Result<Vec<u8>> {
-        let resp = apdu::send_command(
-            self.card_client(),
-            commands::set_identity(id),
-            false,
-        );
+    pub fn set_identity(
+        card_client: &mut dyn CardClient,
+        id: u8,
+    ) -> Result<Vec<u8>> {
+        let resp =
+            apdu::send_command(card_client, commands::set_identity(id), false);
 
         // Apparently it's normal to get "NotTransacted" from pcsclite when
         // the identity switch was successful.
@@ -265,7 +261,7 @@ impl CardApp {
     /// SELECT DATA ("select a DO in the current template",
     /// e.g. for cardholder certificate)
     pub fn select_data(
-        &mut self,
+        card_client: &mut dyn CardClient,
         num: u8,
         tag: &[u8],
     ) -> Result<Response, Error> {
@@ -277,7 +273,7 @@ impl CardApp {
         let data = tlv.serialize();
 
         let cmd = commands::select_data(num, data);
-        apdu::send_command(self.card_client(), cmd, true)?.try_into()
+        apdu::send_command(card_client, cmd, true)?.try_into()
     }
 
     // --- optional private DOs (0101 - 0104) ---
@@ -285,11 +281,14 @@ impl CardApp {
     /// Get data from "private use" DO.
     ///
     /// `num` must be between 1 and 4.
-    pub fn private_use_do(&mut self, num: u8) -> Result<Vec<u8>> {
+    pub fn private_use_do(
+        card_client: &mut dyn CardClient,
+        num: u8,
+    ) -> Result<Vec<u8>> {
         assert!((1..=4).contains(&num));
 
         let cmd = commands::private_use_do(num);
-        let resp = apdu::send_command(self.card_client(), cmd, true)?;
+        let resp = apdu::send_command(card_client, cmd, true)?;
 
         Ok(resp.data()?.to_vec())
     }
@@ -302,14 +301,14 @@ impl CardApp {
     /// - 1/3 need PW1 (82)
     /// - 2/4 need PW3
     pub fn set_private_use_do(
-        &mut self,
+        card_client: &mut dyn CardClient,
         num: u8,
         data: Vec<u8>,
     ) -> Result<Vec<u8>> {
         assert!((1..=4).contains(&num));
 
         let cmd = commands::put_private_use_do(num, data);
-        let resp = apdu::send_command(self.card_client(), cmd, true)?;
+        let resp = apdu::send_command(card_client, cmd, true)?;
 
         Ok(resp.data()?.to_vec())
     }
@@ -331,12 +330,12 @@ impl CardApp {
     /// (However, e.g. vanilla Gnuk doesn't support this functionality.
     /// Gnuk needs to be built with the `--enable-factory-reset`
     /// option to the `configure` script to enable this functionality).
-    pub fn factory_reset(&mut self) -> Result<()> {
+    pub fn factory_reset(card_client: &mut dyn CardClient) -> Result<()> {
         // send 4 bad requests to verify pw1
         // [apdu 00 20 00 81 08 40 40 40 40 40 40 40 40]
         for _ in 0..4 {
             let verify = commands::verify_pw1_81([0x40; 8].to_vec());
-            let resp = apdu::send_command(self.card_client(), verify, false)?;
+            let resp = apdu::send_command(card_client, verify, false)?;
             if !(resp.status() == StatusBytes::SecurityStatusNotSatisfied
                 || resp.status() == StatusBytes::AuthenticationMethodBlocked
                 || matches!(resp.status(), StatusBytes::PasswordNotChecked(_)))
@@ -349,7 +348,7 @@ impl CardApp {
         // [apdu 00 20 00 83 08 40 40 40 40 40 40 40 40]
         for _ in 0..4 {
             let verify = commands::verify_pw3([0x40; 8].to_vec());
-            let resp = apdu::send_command(self.card_client(), verify, false)?;
+            let resp = apdu::send_command(card_client, verify, false)?;
 
             if !(resp.status() == StatusBytes::SecurityStatusNotSatisfied
                 || resp.status() == StatusBytes::AuthenticationMethodBlocked
@@ -361,12 +360,12 @@ impl CardApp {
 
         // terminate_df [apdu 00 e6 00 00]
         let term = commands::terminate_df();
-        let resp = apdu::send_command(self.card_client(), term, false)?;
+        let resp = apdu::send_command(card_client, term, false)?;
         resp.check_ok()?;
 
         // activate_file [apdu 00 44 00 00]
         let act = commands::activate_file();
-        let resp = apdu::send_command(self.card_client(), act, false)?;
+        let resp = apdu::send_command(card_client, act, false)?;
         resp.check_ok()?;
 
         Ok(())
@@ -375,13 +374,13 @@ impl CardApp {
     // --- verify/modify ---
 
     /// Does the cardreader support direct pinpad verify?
-    pub fn feature_pinpad_verify(&self) -> bool {
-        self.card_client.feature_pinpad_verify()
+    pub fn feature_pinpad_verify(card_client: &mut dyn CardClient) -> bool {
+        card_client.feature_pinpad_verify()
     }
 
     /// Does the cardreader support direct pinpad modify?
-    pub fn feature_pinpad_modify(&self) -> bool {
-        self.card_client.feature_pinpad_modify()
+    pub fn feature_pinpad_modify(card_client: &mut dyn CardClient) -> bool {
+        card_client.feature_pinpad_modify()
     }
 
     /// Verify pw1 (user) for signing operation (mode 81).
@@ -390,11 +389,11 @@ impl CardApp {
     /// access condition is only valid for one PSO:CDS command or remains
     /// valid for several attempts.
     pub fn verify_pw1_for_signing(
-        &mut self,
+        card_client: &mut dyn CardClient,
         pin: &str,
     ) -> Result<Response, Error> {
         let verify = commands::verify_pw1_81(pin.as_bytes().to_vec());
-        apdu::send_command(self.card_client(), verify, false)?.try_into()
+        apdu::send_command(card_client, verify, false)?.try_into()
     }
 
     /// Verify pw1 (user) for signing operation (mode 81) using a
@@ -405,9 +404,9 @@ impl CardApp {
     /// access condition is only valid for one PSO:CDS command or remains
     /// valid for several attempts.
     pub fn verify_pw1_for_signing_pinpad(
-        &mut self,
+        card_client: &mut dyn CardClient,
     ) -> Result<Response, Error> {
-        let res = self.card_client.pinpad_verify(0x81)?;
+        let res = card_client.pinpad_verify(0x81)?;
         RawResponse::try_from(res)?.try_into()
     }
 
@@ -417,24 +416,31 @@ impl CardApp {
     ///
     /// (Note: some cards don't correctly implement this feature,
     /// e.g. YubiKey 5)
-    pub fn check_pw1_for_signing(&mut self) -> Result<Response, Error> {
+    pub fn check_pw1_for_signing(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
         let verify = commands::verify_pw1_81(vec![]);
-        apdu::send_command(self.card_client(), verify, false)?.try_into()
+        apdu::send_command(card_client, verify, false)?.try_into()
     }
 
     /// Verify PW1 (user).
     /// (For operations except signing, mode 82).
-    pub fn verify_pw1(&mut self, pin: &str) -> Result<Response, Error> {
+    pub fn verify_pw1(
+        card_client: &mut dyn CardClient,
+        pin: &str,
+    ) -> Result<Response, Error> {
         let verify = commands::verify_pw1_82(pin.as_bytes().to_vec());
-        apdu::send_command(self.card_client(), verify, false)?.try_into()
+        apdu::send_command(card_client, verify, false)?.try_into()
     }
 
     /// Verify PW1 (user) for operations except signing (mode 82),
     /// using a pinpad on the card reader. If no usable pinpad is found,
     /// an error is returned.
 
-    pub fn verify_pw1_pinpad(&mut self) -> Result<Response, Error> {
-        let res = self.card_client.pinpad_verify(0x82)?;
+    pub fn verify_pw1_pinpad(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
+        let res = card_client.pinpad_verify(0x82)?;
         RawResponse::try_from(res)?.try_into()
     }
 
@@ -445,21 +451,28 @@ impl CardApp {
     ///
     /// (Note: some cards don't correctly implement this feature,
     /// e.g. YubiKey 5)
-    pub fn check_pw1(&mut self) -> Result<Response, Error> {
+    pub fn check_pw1(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
         let verify = commands::verify_pw1_82(vec![]);
-        apdu::send_command(self.card_client(), verify, false)?.try_into()
+        apdu::send_command(card_client, verify, false)?.try_into()
     }
 
     /// Verify PW3 (admin).
-    pub fn verify_pw3(&mut self, pin: &str) -> Result<Response, Error> {
+    pub fn verify_pw3(
+        card_client: &mut dyn CardClient,
+        pin: &str,
+    ) -> Result<Response, Error> {
         let verify = commands::verify_pw3(pin.as_bytes().to_vec());
-        apdu::send_command(self.card_client(), verify, false)?.try_into()
+        apdu::send_command(card_client, verify, false)?.try_into()
     }
 
     /// Verify PW3 (admin) using a pinpad on the card reader. If no usable
     /// pinpad is found, an error is returned.
-    pub fn verify_pw3_pinpad(&mut self) -> Result<Response, Error> {
-        let res = self.card_client.pinpad_verify(0x83)?;
+    pub fn verify_pw3_pinpad(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
+        let res = card_client.pinpad_verify(0x83)?;
         RawResponse::try_from(res)?.try_into()
     }
 
@@ -469,16 +482,18 @@ impl CardApp {
     ///
     /// (Note: some cards don't correctly implement this feature,
     /// e.g. YubiKey 5)
-    pub fn check_pw3(&mut self) -> Result<Response, Error> {
+    pub fn check_pw3(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
         let verify = commands::verify_pw3(vec![]);
-        apdu::send_command(self.card_client(), verify, false)?.try_into()
+        apdu::send_command(card_client, verify, false)?.try_into()
     }
 
     /// Change the value of PW1 (user password).
     ///
     /// The current value of PW1 must be presented in `old` for authorization.
     pub fn change_pw1(
-        &mut self,
+        card_client: &mut dyn CardClient,
         old: &str,
         new: &str,
     ) -> Result<Response, Error> {
@@ -487,13 +502,15 @@ impl CardApp {
         data.extend(new.as_bytes());
 
         let change = commands::change_pw1(data);
-        apdu::send_command(self.card_client(), change, false)?.try_into()
+        apdu::send_command(card_client, change, false)?.try_into()
     }
 
     /// Change the value of PW1 (user password)  using a pinpad on the
     /// card reader. If no usable pinpad is found, an error is returned.
-    pub fn change_pw1_pinpad(&mut self) -> Result<Response, Error> {
-        let res = self.card_client.pinpad_modify(0x81)?;
+    pub fn change_pw1_pinpad(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
+        let res = card_client.pinpad_modify(0x81)?;
         RawResponse::try_from(res)?.try_into()
     }
 
@@ -501,7 +518,7 @@ impl CardApp {
     ///
     /// The current value of PW3 must be presented in `old` for authorization.
     pub fn change_pw3(
-        &mut self,
+        card_client: &mut dyn CardClient,
         old: &str,
         new: &str,
     ) -> Result<Response, Error> {
@@ -510,13 +527,15 @@ impl CardApp {
         data.extend(new.as_bytes());
 
         let change = commands::change_pw3(data);
-        apdu::send_command(self.card_client(), change, false)?.try_into()
+        apdu::send_command(card_client, change, false)?.try_into()
     }
 
     /// Change the value of PW3 (admin password) using a pinpad on the
     /// card reader. If no usable pinpad is found, an error is returned.
-    pub fn change_pw3_pinpad(&mut self) -> Result<Response, Error> {
-        let res = self.card_client.pinpad_modify(0x83)?;
+    pub fn change_pw3_pinpad(
+        card_client: &mut dyn CardClient,
+    ) -> Result<Response, Error> {
+        let res = card_client.pinpad_modify(0x83)?;
         RawResponse::try_from(res)?.try_into()
     }
 
@@ -528,12 +547,12 @@ impl CardApp {
     /// - secure messaging must be currently used,
     /// - the resetting_code must be presented.
     pub fn reset_retry_counter_pw1(
-        &mut self,
+        card_client: &mut dyn CardClient,
         new_pw1: Vec<u8>,
         resetting_code: Option<Vec<u8>>,
     ) -> Result<Response, Error> {
         let reset = commands::reset_retry_counter_pw1(resetting_code, new_pw1);
-        apdu::send_command(self.card_client(), reset, false)?.try_into()
+        apdu::send_command(card_client, reset, false)?.try_into()
     }
 
     // --- decrypt ---
@@ -542,7 +561,10 @@ impl CardApp {
     ///
     /// (This is a wrapper around the low-level pso_decipher
     /// operation, it builds the required `data` field from `dm`)
-    pub fn decipher(&mut self, dm: Cryptogram) -> Result<Vec<u8>, Error> {
+    pub fn decipher(
+        card_client: &mut dyn CardClient,
+        dm: Cryptogram,
+    ) -> Result<Vec<u8>, Error> {
         match dm {
             Cryptogram::RSA(message) => {
                 // "Padding indicator byte (00) for RSA" (pg. 69)
@@ -550,7 +572,7 @@ impl CardApp {
                 data.extend_from_slice(message);
 
                 // Call the card to decrypt `data`
-                self.pso_decipher(data)
+                Self::pso_decipher(card_client, data)
             }
             Cryptogram::ECDH(eph) => {
                 // "In case of ECDH the card supports a partial decrypt
@@ -568,17 +590,20 @@ impl CardApp {
                 // Cipher DO
                 let cdo = Tlv::new([0xa6], Value::C(vec![pkdo]));
 
-                self.pso_decipher(cdo.serialize())
+                Self::pso_decipher(card_client, cdo.serialize())
             }
         }
     }
 
     /// Run decryption operation on the smartcard (low level operation)
     /// (7.2.11 PSO: DECIPHER)
-    fn pso_decipher(&mut self, data: Vec<u8>) -> Result<Vec<u8>, Error> {
+    fn pso_decipher(
+        card_client: &mut dyn CardClient,
+        data: Vec<u8>,
+    ) -> Result<Vec<u8>, Error> {
         // The OpenPGP card is already connected and PW1 82 has been verified
         let dec_cmd = commands::decryption(data);
-        let resp = apdu::send_command(self.card_client(), dec_cmd, true)?;
+        let resp = apdu::send_command(card_client, dec_cmd, true)?;
         resp.check_ok()?;
 
         Ok(resp.data().map(|d| d.to_vec())?)
@@ -626,21 +651,24 @@ impl CardApp {
     /// With ECC the hash data is processed as is, using
     /// pso_compute_digital_signature.
     pub fn signature_for_hash(
-        &mut self,
+        card_client: &mut dyn CardClient,
         hash: Hash,
     ) -> Result<Vec<u8>, Error> {
-        self.pso_compute_digital_signature(Self::digestinfo(hash))
+        Self::pso_compute_digital_signature(
+            card_client,
+            Self::digestinfo(hash),
+        )
     }
 
     /// Run signing operation on the smartcard (low level operation)
     /// (7.2.10 PSO: COMPUTE DIGITAL SIGNATURE)
     pub fn pso_compute_digital_signature(
-        &mut self,
+        card_client: &mut dyn CardClient,
         data: Vec<u8>,
     ) -> Result<Vec<u8>, Error> {
         let cds_cmd = commands::signature(data);
 
-        let resp = apdu::send_command(self.card_client(), cds_cmd, true)?;
+        let resp = apdu::send_command(card_client, cds_cmd, true)?;
 
         Ok(resp.data().map(|d| d.to_vec())?)
     }
@@ -658,48 +686,60 @@ impl CardApp {
     ///
     /// With ECC the hash data is processed as is.
     pub fn authenticate_for_hash(
-        &mut self,
+        card_client: &mut dyn CardClient,
         hash: Hash,
     ) -> Result<Vec<u8>, Error> {
-        self.internal_authenticate(Self::digestinfo(hash))
+        Self::internal_authenticate(card_client, Self::digestinfo(hash))
     }
 
     /// Run signing operation on the smartcard (low level operation)
     /// (7.2.13 INTERNAL AUTHENTICATE)
     pub fn internal_authenticate(
-        &mut self,
+        card_client: &mut dyn CardClient,
         data: Vec<u8>,
     ) -> Result<Vec<u8>, Error> {
         let ia_cmd = commands::internal_authenticate(data);
-        let resp = apdu::send_command(self.card_client(), ia_cmd, true)?;
+        let resp = apdu::send_command(card_client, ia_cmd, true)?;
 
         Ok(resp.data().map(|d| d.to_vec())?)
     }
 
     // --- admin ---
 
-    pub fn set_name(&mut self, name: &str) -> Result<Response, Error> {
+    pub fn set_name(
+        card_client: &mut dyn CardClient,
+        name: &str,
+    ) -> Result<Response, Error> {
         let put_name = commands::put_name(name.as_bytes().to_vec());
-        apdu::send_command(self.card_client(), put_name, false)?.try_into()
+        apdu::send_command(card_client, put_name, false)?.try_into()
     }
 
-    pub fn set_lang(&mut self, lang: &str) -> Result<Response, Error> {
+    pub fn set_lang(
+        card_client: &mut dyn CardClient,
+        lang: &str,
+    ) -> Result<Response, Error> {
         let put_lang = commands::put_lang(lang.as_bytes().to_vec());
-        apdu::send_command(self.card_client(), put_lang, false)?.try_into()
+        apdu::send_command(card_client, put_lang, false)?.try_into()
     }
 
-    pub fn set_sex(&mut self, sex: Sex) -> Result<Response, Error> {
+    pub fn set_sex(
+        card_client: &mut dyn CardClient,
+        sex: Sex,
+    ) -> Result<Response, Error> {
         let put_sex = commands::put_sex((&sex).into());
-        apdu::send_command(self.card_client(), put_sex, false)?.try_into()
+        apdu::send_command(card_client, put_sex, false)?.try_into()
     }
 
-    pub fn set_url(&mut self, url: &str) -> Result<Response, Error> {
+    pub fn set_url(
+        card_client: &mut dyn CardClient,
+        url: &str,
+    ) -> Result<Response, Error> {
         let put_url = commands::put_url(url.as_bytes().to_vec());
-        apdu::send_command(self.card_client(), put_url, false)?.try_into()
+        apdu::send_command(card_client, put_url, false)?.try_into()
     }
 
     pub fn set_creation_time(
-        &mut self,
+        card_client: &mut dyn CardClient,
         time: KeyGenerationTime,
         key_type: KeyType,
     ) -> Result<Response, Error> {
@@ -715,11 +755,11 @@ impl CardApp {
         let time_cmd =
             commands::put_data(&[key_type.timestamp_put_tag()], time_value);
 
-        apdu::send_command(self.card_client(), time_cmd, false)?.try_into()
+        apdu::send_command(card_client, time_cmd, false)?.try_into()
     }
 
     pub fn set_fingerprint(
-        &mut self,
+        card_client: &mut dyn CardClient,
         fp: Fingerprint,
         key_type: KeyType,
     ) -> Result<Response, Error> {
@@ -728,7 +768,7 @@ impl CardApp {
             fp.as_bytes().to_vec(),
         );
 
-        apdu::send_command(self.card_client(), fp_cmd, false)?.try_into()
+        apdu::send_command(card_client, fp_cmd, false)?.try_into()
     }
 
     /// Set PW Status Bytes.
@@ -743,14 +783,14 @@ impl CardApp {
     ///
     /// (See OpenPGP card spec, pg. 28)
     pub fn set_pw_status_bytes(
-        &mut self,
+        card_client: &mut dyn CardClient,
         pw_status: &PWStatusBytes,
         long: bool,
     ) -> Result<Response, Error> {
         let data = pw_status.serialize_for_put(long);
 
         let cmd = commands::put_pw_status(data);
-        apdu::send_command(self.card_client(), cmd, false)?.try_into()
+        apdu::send_command(card_client, cmd, false)?.try_into()
     }
 
     /// Set cardholder certificate (for AUT, DEC or SIG).
@@ -758,17 +798,17 @@ impl CardApp {
     /// Call select_data() before calling this fn, to select a particular
     /// certificate (if the card supports multiple certificates).
     pub fn set_cardholder_certificate(
-        &mut self,
+        card_client: &mut dyn CardClient,
         data: Vec<u8>,
     ) -> Result<Response, Error> {
         let cmd = commands::put_cardholder_certificate(data);
-        apdu::send_command(self.card_client(), cmd, false)?.try_into()
+        apdu::send_command(card_client, cmd, false)?.try_into()
     }
 
     /// Set algorithm attributes
     /// (4.4.3.9 Algorithm Attributes)
     pub fn set_algorithm_attributes(
-        &mut self,
+        card_client: &mut dyn CardClient,
         key_type: KeyType,
         algo: &Algo,
     ) -> Result<Response, Error> {
@@ -778,33 +818,33 @@ impl CardApp {
             algo.to_data_object()?,
         );
 
-        apdu::send_command(self.card_client(), cmd, false)?.try_into()
+        apdu::send_command(card_client, cmd, false)?.try_into()
     }
 
     /// Set resetting code
     /// (4.3.4 Resetting Code)
     pub fn set_resetting_code(
-        &mut self,
+        card_client: &mut dyn CardClient,
         resetting_code: Vec<u8>,
     ) -> Result<Response, Error> {
         let cmd = commands::put_data(&[0xd3], resetting_code);
-        apdu::send_command(self.card_client(), cmd, false)?.try_into()
+        apdu::send_command(card_client, cmd, false)?.try_into()
     }
 
     /// Import an existing private key to the card.
     /// (This implicitly sets the algorithm info, fingerprint and timestamp)
     pub fn key_import(
-        &mut self,
+        card_client: &mut dyn CardClient,
         key: Box<dyn CardUploadableKey>,
         key_type: KeyType,
     ) -> Result<(), Error> {
-        let algo_info = self.algorithm_information();
+        let algo_info = Self::algorithm_information(card_client);
 
         // An error is ok - it's fine if a card doesn't offer a list of
         // supported algorithms
         let algo_info = algo_info.unwrap_or(None);
 
-        keys::key_import(self, key, key_type, algo_info)
+        keys::key_import(card_client, key, key_type, algo_info)
     }
 
     /// Generate a key on the card.
@@ -817,7 +857,7 @@ impl CardApp {
     /// applicable), and import format, with values that the current card
     /// supports.
     pub fn generate_key(
-        &mut self,
+        card_client: &mut dyn CardClient,
         fp_from_pub: fn(
             &PublicKeyMaterial,
             KeyGenerationTime,
@@ -826,7 +866,7 @@ impl CardApp {
         key_type: KeyType,
         algo: Option<&Algo>,
     ) -> Result<(PublicKeyMaterial, KeyGenerationTime), Error> {
-        keys::gen_key_with_metadata(self, fp_from_pub, key_type, algo)
+        keys::gen_key_with_metadata(card_client, fp_from_pub, key_type, algo)
     }
 
     /// Generate a key on the card.
@@ -839,7 +879,7 @@ impl CardApp {
     /// bitsize of e for RSA, and import format). This function determines
     /// these values based on information from the card.
     pub fn generate_key_simple(
-        &mut self,
+        card_client: &mut dyn CardClient,
         fp_from_pub: fn(
             &PublicKeyMaterial,
             KeyGenerationTime,
@@ -848,16 +888,17 @@ impl CardApp {
         key_type: KeyType,
         simple: AlgoSimple,
     ) -> Result<(PublicKeyMaterial, KeyGenerationTime), Error> {
-        let ard = self.application_related_data()?;
-        let algo_info = if let Ok(ai) = self.algorithm_information() {
-            ai
-        } else {
-            None
-        };
+        let ard = Self::application_related_data(card_client)?;
+        let algo_info =
+            if let Ok(ai) = Self::algorithm_information(card_client) {
+                ai
+            } else {
+                None
+            };
 
         let algo = simple.determine_algo(key_type, &ard, algo_info)?;
 
-        self.generate_key(fp_from_pub, key_type, Some(&algo))
+        Self::generate_key(card_client, fp_from_pub, key_type, Some(&algo))
     }
 
     /// Get public key material from the card.
@@ -869,9 +910,9 @@ impl CardApp {
     /// reconstruct a pre-existing OpenPGP public key that corresponds to
     /// the private key on the card.
     pub fn public_key(
-        &mut self,
+        card_client: &mut dyn CardClient,
         key_type: KeyType,
     ) -> Result<PublicKeyMaterial, Error> {
-        keys::public_key(self, key_type)
+        keys::public_key(card_client, key_type)
     }
 }
diff --git a/openpgp-card/src/keys.rs b/openpgp-card/src/keys.rs
index 08c6dec..01a7b7d 100644
--- a/openpgp-card/src/keys.rs
+++ b/openpgp-card/src/keys.rs
@@ -17,8 +17,8 @@ use crate::crypto_data::{
     PublicKeyMaterial, RSAKey, RSAPub,
 };
 use crate::tlv::{length::tlv_encode_length, value::Value, Tlv};
-use crate::Error;
 use crate::{apdu, KeyType};
+use crate::{CardClient, Error};
 
 /// Generate asymmetric key pair on the card.
 ///
@@ -31,7 +31,7 @@ use crate::{apdu, KeyType};
 /// `fp_from_pub` calculates the fingerprint for a public key data object and
 /// creation timestamp
 pub(crate) fn gen_key_with_metadata(
-    card_app: &mut CardApp,
+    card_client: &mut dyn CardClient,
     fp_from_pub: fn(
         &PublicKeyMaterial,
         KeyGenerationTime,
@@ -43,12 +43,16 @@ pub(crate) fn gen_key_with_metadata(
     // Set algo on card if it's Some
     if let Some(target_algo) = algo {
         // FIXME: caching
-        let ard = card_app.application_related_data()?; // no caching, here!
+        let ard = CardApp::application_related_data(card_client)?; // no caching, here!
         let ecap = ard.extended_capabilities()?;
 
         // Only set algo if card supports setting of algo attr
         if ecap.algo_attrs_changeable() {
-            card_app.set_algorithm_attributes(key_type, target_algo)?;
+            CardApp::set_algorithm_attributes(
+                card_client,
+                key_type,
+                target_algo,
+            )?;
         } else {
             // Check if the current algo on the card is the one we want, if
             // not we return an error.
@@ -65,11 +69,11 @@ pub(crate) fn gen_key_with_metadata(
     }
 
     // get current (possibly updated) state of algo
-    let ard = card_app.application_related_data()?; // no caching, here!
+    let ard = CardApp::application_related_data(card_client)?; // no caching, here!
     let cur_algo = ard.algorithm_attributes(key_type)?;
 
     // generate key
-    let tlv = generate_asymmetric_key_pair(card_app, key_type)?;
+    let tlv = generate_asymmetric_key_pair(card_client, key_type)?;
 
     // derive pubkey
     let pubkey = tlv_to_pubkey(&tlv, &cur_algo)?;
@@ -87,11 +91,11 @@ pub(crate) fn gen_key_with_metadata(
 
     let ts = ts.into();
 
-    card_app.set_creation_time(ts, key_type)?;
+    CardApp::set_creation_time(card_client, ts, key_type)?;
 
     // calculate/store fingerprint
     let fp = fp_from_pub(&pubkey, ts, key_type)?;
-    card_app.set_fingerprint(fp, key_type)?;
+    CardApp::set_fingerprint(card_client, fp, key_type)?;
 
     Ok((pubkey, ts))
 }
@@ -128,14 +132,14 @@ fn tlv_to_pubkey(tlv: &Tlv, algo: &Algo) -> Result<PublicKeyMaterial> {
 /// This runs the low level key generation primitive on the card.
 /// (This does not set algorithm attributes, creation time or fingerprint)
 pub(crate) fn generate_asymmetric_key_pair(
-    card_app: &mut CardApp,
+    card_client: &mut dyn CardClient,
     key_type: KeyType,
 ) -> Result<Tlv, Error> {
     // generate key
     let crt = control_reference_template(key_type)?;
     let gen_key_cmd = commands::gen_key(crt.serialize().to_vec());
 
-    let resp = apdu::send_command(card_app.card_client(), gen_key_cmd, true)?;
+    let resp = apdu::send_command(card_client, gen_key_cmd, true)?;
     resp.check_ok()?;
 
     let tlv = Tlv::try_from(resp.data()?)?;
@@ -150,19 +154,18 @@ pub(crate) fn generate_asymmetric_key_pair(
 ///
 /// (See 7.2.14 GENERATE ASYMMETRIC KEY PAIR)
 pub(crate) fn public_key(
-    card_app: &mut CardApp,
+    card_client: &mut dyn CardClient,
     key_type: KeyType,
 ) -> Result<PublicKeyMaterial, Error> {
     // get current algo
-    let ard = card_app.application_related_data()?; // FIXME: caching
+    let ard = CardApp::application_related_data(card_client)?; // FIXME: caching
     let algo = ard.algorithm_attributes(key_type)?;
 
     // get public key
     let crt = control_reference_template(key_type)?;
     let get_pub_key_cmd = commands::get_pub_key(crt.serialize().to_vec());
 
-    let resp =
-        apdu::send_command(card_app.card_client(), get_pub_key_cmd, true)?;
+    let resp = apdu::send_command(card_client, get_pub_key_cmd, true)?;
     resp.check_ok()?;
 
     let tlv = Tlv::try_from(resp.data()?)?;
@@ -177,13 +180,13 @@ pub(crate) fn public_key(
 /// caused by checks before attempting to upload the key to the card, or by
 /// an error that the card reports during an attempt to upload the key).
 pub(crate) fn key_import(
-    card_app: &mut CardApp,
+    card_client: &mut dyn CardClient,
     key: Box<dyn CardUploadableKey>,
     key_type: KeyType,
     algo_info: Option<AlgoInfo>,
 ) -> Result<(), Error> {
     // FIXME: caching?
-    let ard = card_app.application_related_data()?;
+    let ard = CardApp::application_related_data(card_client)?;
 
     let (algo, key_cmd) = match key.private_key()? {
         PrivateKeyMaterial::R(rsa_key) => {
@@ -219,12 +222,12 @@ pub(crate) fn key_import(
 
     // Only set algo attrs if "Extended Capabilities" lists the feature
     if ard.extended_capabilities()?.algo_attrs_changeable() {
-        card_app.set_algorithm_attributes(key_type, &algo)?;
+        CardApp::set_algorithm_attributes(card_client, key_type, &algo)?;
     }
 
-    apdu::send_command(card_app.card_client(), key_cmd, false)?.check_ok()?;
-    card_app.set_fingerprint(fp, key_type)?;
-    card_app.set_creation_time(key.timestamp(), key_type)?;
+    apdu::send_command(card_client, key_cmd, false)?.check_ok()?;
+    CardApp::set_fingerprint(card_client, fp, key_type)?;
+    CardApp::set_creation_time(card_client, key.timestamp(), key_type)?;
 
     Ok(())
 }
diff --git a/pcsc/src/lib.rs b/pcsc/src/lib.rs
index 0081f7f..147456b 100644
--- a/pcsc/src/lib.rs
+++ b/pcsc/src/lib.rs
@@ -236,8 +236,8 @@ impl PcscClient {
         }
     }
 
-    fn cards_filter(ident: Option<&str>) -> Result<Vec<CardApp>, Error> {
-        let mut cas: Vec<CardApp> = vec![];
+    fn cards_filter(ident: Option<&str>) -> Result<Vec<PcscClient>, Error> {
+        let mut cas: Vec<PcscClient> = vec![];
 
         for mut card in
             Self::raw_pcsc_cards().map_err(|sce| Error::Smartcard(sce))?
@@ -316,14 +316,14 @@ impl PcscClient {
     ///
     /// Each card has the OpenPGP application selected, CardCaps have been
     /// initialized.
-    pub fn cards() -> Result<Vec<CardApp>, Error> {
+    pub fn cards() -> Result<Vec<PcscClient>, Error> {
         Self::cards_filter(None)
     }
 
     /// Returns the OpenPGP card that matches `ident`, if it is available.
     /// A fully initialized CardApp is returned: the OpenPGP application has
     /// been selected, CardCaps have been set.
-    pub fn open_by_ident(ident: &str) -> Result<CardApp, Error> {
+    pub fn open_by_ident(ident: &str) -> Result<PcscClient, Error> {
         log::debug!("open_by_ident for {:?}", ident);
 
         let mut cards = Self::cards_filter(Some(ident))?;
@@ -349,7 +349,7 @@ impl PcscClient {
 
     /// Make an initialized CardApp from a PcscClient.
     /// Obtain and store feature lists from reader (pinpad functionality).
-    fn into_card_app(mut self) -> Result<CardApp> {
+    fn into_card_app(mut self) -> Result<Self> {
         // Get Features from reader (pinpad verify/modify)
         if let Ok(feat) = self.features() {
             for tlv in feat {
@@ -359,7 +359,9 @@ impl PcscClient {
         }
 
         // Get initalized CardApp
-        CardApp::initialize(Box::new(self))
+        CardApp::initialize(&mut self)?;
+
+        Ok(self)
     }
 
     /// Get the minimum pin length for pin_id.
diff --git a/scdc/src/lib.rs b/scdc/src/lib.rs
index 1eba7d8..82481ee 100644
--- a/scdc/src/lib.rs
+++ b/scdc/src/lib.rs
@@ -62,11 +62,13 @@ impl ScdClient {
     pub fn open_by_serial(
         agent: Option<Agent>,
         serial: &str,
-    ) -> Result<CardApp, Error> {
+    ) -> Result<Self, Error> {
         let mut card = ScdClient::new(agent, true)?;
         card.select_card(serial)?;
 
-        Ok(CardApp::initialize(Box::new(card))?)
+        CardApp::initialize(&mut card)?;
+
+        Ok(card)
     }
 
     /// Open a CardApp that uses an scdaemon instance as its backend.
@@ -75,10 +77,12 @@ impl ScdClient {
     ///
     /// (NOTE: implicitly picking an unspecified card might be a bad idea.
     /// You might want to avoid using this function.)
-    pub fn open_yolo(agent: Option<Agent>) -> Result<CardApp, Error> {
-        let card = ScdClient::new(agent, true)?;
+    pub fn open_yolo(agent: Option<Agent>) -> Result<Self, Error> {
+        let mut card = ScdClient::new(agent, true)?;
 
-        Ok(CardApp::initialize(Box::new(card))?)
+        CardApp::initialize(&mut card)?;
+
+        Ok(card)
     }
 
     /// Helper fn that shuts down scdaemon via GnuPG Agent.