adjust find_suitable_key() to prefer PQC subkeys

pqc-thunderbird · Apr 24, 2024 · 1273f51 · 1273f51
1 parent 81dc47c
commit 1273f51
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diff --git a/src/lib/pgp-key.cpp b/src/lib/pgp-key.cpp
@@ -471,6 +471,19 @@ find_suitable_key(pgp_op_t op, pgp_key_t *key, rnp::KeyProvider *key_provider, b
         if (!cur || !cur->usable_for(op)) {
             continue;
         }
+#if defined(ENABLE_PQC)
+        /* prefer PQC over non-PQC. Assume non-PQC key is only there for backwards
+         * compatibility. */
+        if (subkey && subkey->is_pqc_alg() && !cur->is_pqc_alg()) {
+            /* do not override already found PQC key with non-PQC key */
+            continue;
+        }
+        if (subkey && cur->is_pqc_alg() && !subkey->is_pqc_alg()) {
+            /* override non-PQC key with PQC key */
+            subkey = cur;
+            continue;
+        }
+#endif
         if (!subkey || (cur->creation() > subkey->creation())) {
             subkey = cur;
         }
@@ -1330,6 +1343,41 @@ pgp_key_t::has_secret() const
     }
 }
 
+#if defined(ENABLE_PQC)
+bool
+pgp_key_t::is_pqc_alg() const
+{
+    switch (alg()) {
+    case PGP_PKA_KYBER768_X25519:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_KYBER768_P256:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_KYBER1024_P384:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_KYBER768_BP256:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_KYBER1024_BP384:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_DILITHIUM3_ED25519:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_DILITHIUM3_P256:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_DILITHIUM5_P384:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_DILITHIUM3_BP256:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_DILITHIUM5_BP384:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_SPHINCSPLUS_SHA2:
+        FALLTHROUGH_STATEMENT;
+    case PGP_PKA_SPHINCSPLUS_SHAKE:
+        return true;
+    default:
+        return false;
+    }
+}
+#endif
+
 bool
 pgp_key_t::usable_for(pgp_op_t op, bool if_secret) const
 {

diff --git a/src/lib/pgp-key.h b/src/lib/pgp-key.h
@@ -227,6 +227,9 @@ struct pgp_key_t {
     bool             can_certify() const;
     bool             can_encrypt() const;
     bool             has_secret() const;
+#if defined(ENABLE_PQC)
+    bool is_pqc_alg() const;
+#endif
     /**
      * @brief Check whether key is usable for the specified operation.
      *