Implement next_cardholder_certificate() to read successive cardholder certificates from the card.

openpgp-card-sequoia/src/card.rs

@@ -271,6 +271,14 @@ impl<'a> Open<'a> {
         self.opt.security_support_template()
     }
 
+    /// "GET NEXT DATA" for the DO cardholder certificate.
+    ///
+    /// Cardholder certificate data for multiple slots can be read from the card by first calling
+    /// cardholder_certificate(), followed by up to two calls to  next_cardholder_certificate().
+    pub fn next_cardholder_certificate(&mut self) -> Result<Vec<u8>, Error> {
+        self.opt.next_cardholder_certificate()
+    }
+
     // DO "Algorithm Information" (0xFA)
     pub fn algorithm_information(&mut self) -> Result<Option<AlgoInfo>, Error> {
         // The DO "Algorithm Information" (Tag FA) shall be present if

openpgp-card/src/apdu/commands.rs

@@ -62,6 +62,11 @@ pub(crate) fn cardholder_certificate() -> Command {
     get_data(Tags::CardholderCertificate)
 }
 
+/// GET NEXT DATA for DO "Cardholder certificate"
+pub(crate) fn get_next_cardholder_certificate() -> Command {
+    Command::new(0x00, 0xCC, 0x7f, 0x21, vec![])
+}
+
 /// GET DO "Algorithm Information"
 pub(crate) fn algo_info() -> Command {
     get_data(Tags::AlgorithmInformation)

openpgp-card/src/openpgp.rs

@@ -149,6 +149,17 @@ impl<'a> OpenPgpTransaction<'a> {
         apdu::send_command(self.tx(), cmd, true)?.try_into()
     }
 
+    /// Call "GET NEXT DATA" for the DO cardholder certificate.
+    ///
+    /// Cardholder certificate data for multiple slots can be read from the card by first calling
+    /// cardholder_certificate(), followed by up to two calls to  next_cardholder_certificate().
+    pub fn next_cardholder_certificate(&mut self) -> Result<Vec<u8>, Error> {
+        log::info!("OpenPgpTransaction: next_cardholder_certificate");
+
+        let cmd = commands::get_next_cardholder_certificate();
+        apdu::send_command(self.tx(), cmd, true)?.try_into()
+    }
+
     /// Get "Algorithm Information"
     pub fn algorithm_information(&mut self) -> Result<Option<AlgoInfo>, Error> {
         log::info!("OpenPgpTransaction: algorithm_information");