openpgp-card: Add matching_algorithm_attributes() in AlgoSimple

Gets matching AlgorithmAttributes for the current card.

openpgp-card-sequoia/src/lib.rs

@@ -969,9 +969,12 @@ impl Card<Admin<'_, '_>> {
         key_type: KeyType,
         algo: Option<AlgoSimple>,
     ) -> Result<(PublicKeyMaterial, KeyGenerationTime), Error> {
-        match algo {
-            Some(algo) => self.card().generate_key_simple(Self::ptf, key_type, algo),
-            None => self.card().generate_key(Self::ptf, key_type, None),
+        if let Some(algo) = algo {
+            // set algorithm attributes
+            let attr = algo.matching_algorithm_attributes(self.card(), key_type)?;
+            self.card().set_algorithm_attributes(key_type, &attr)?;
         }
+
+        self.card().generate_key(Self::ptf, key_type, None)
     }
 }

openpgp-card/src/algorithm.rs

@@ -13,7 +13,7 @@ use std::convert::TryFrom;
 use std::fmt;
 
 use crate::crypto_data::EccType;
-use crate::{keys, oid, Error, KeyType};
+use crate::{keys, oid, Error, KeyType, Transaction};
 
 /// A shorthand way to specify algorithms (e.g. for key generation).
 #[derive(Clone, Copy, Debug)]
@@ -50,6 +50,25 @@ impl TryFrom<&str> for AlgoSimple {
 }
 
 impl AlgoSimple {
+    /// Get algorithm attributes for slot `key_type` from this AlgoSimple.
+    ///
+    /// AlgoSimple doesn't specify card specific details (such as bit-size
+    /// of e for RSA, and import format).
+    /// This function determines these values based on information from the
+    /// card behind `tx`.
+    pub fn matching_algorithm_attributes(
+        &self,
+        tx: &mut Transaction,
+        key_type: KeyType,
+    ) -> Result<AlgorithmAttributes, Error> {
+        let ard = tx.application_related_data()?;
+        let algorithm_attributes = ard.algorithm_attributes(key_type)?;
+
+        let algo_info = tx.algorithm_information_cached().ok().flatten();
+
+        self.determine_algo_attributes(key_type, algorithm_attributes, algo_info)
+    }
+
     /// Get corresponding EccType by KeyType (except for Curve25519)
     fn ecc_type(key_type: KeyType) -> EccType {
         match key_type {