irmd: Add issuer and digest pinning to OAP

A peer certificate that verifies against the CA store could have
been issued by any trusted CA, and a peer could pick any supported
digest for its signature. Tighten the authentication contract with
two local policies.

cacert= pins the issuing CA: a peer certificate, if presented, must
chain through the pinned CA. Whether a certificate is mandatory at
all remains controlled by auth= alone.

digest= now also pins the signature digest: a classical peer must sign
with the locally configured digest, and may not omit the digest NID to
fall back to the key's default digest. PQC signatures (ML-DSA,
SLH-DSA) have an intrinsic digest and may be NID_undef.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/irmd/oap/tests/oap_test_ml_dsa.c b/src/irmd/oap/tests/oap_test_ml_dsa.c
index 81b307ab..19be7400 100644
--- a/src/irmd/oap/tests/oap_test_ml_dsa.c
+++ b/src/irmd/oap/tests/oap_test_ml_dsa.c
@@ -237,6 +237,23 @@ static int test_oap_roundtrip_auth_only(void)
         return roundtrip_auth_only(root_ca_crt_ml, im_ca_crt_ml);
 }
 
+/* Digest pin does not apply to PQC: the digest is intrinsic */
+static int test_oap_cli_md_pin_exempts_pqc(void)
+{
+        test_cfg_init(NID_undef, NID_undef, NID_undef, 0, NO_CLI_AUTH);
+        test_cfg.cli.md = NID_sha256;
+
+        return roundtrip_auth_only(root_ca_crt_ml, im_ca_crt_ml);
+}
+
+static int test_oap_srv_md_pin_exempts_pqc(void)
+{
+        test_cfg_init(NID_undef, NID_undef, NID_undef, 0, CLI_AUTH);
+        test_cfg.srv.md = NID_sha256;
+
+        return roundtrip_auth_only(root_ca_crt_ml, im_ca_crt_ml);
+}
+
 static int test_oap_corrupted_request(void)
 {
         test_cfg_init(NID_MLKEM768, NID_aes_256_gcm, get_random_kdf(),
@@ -422,6 +439,8 @@ int oap_test_ml_dsa(int    argc,
 
 #ifdef HAVE_OPENSSL_ML_KEM
         ret |= test_oap_roundtrip_auth_only();
+        ret |= test_oap_cli_md_pin_exempts_pqc();
+        ret |= test_oap_srv_md_pin_exempts_pqc();
 
         ret |= test_oap_roundtrip_kem_all();
 
@@ -432,6 +451,8 @@ int oap_test_ml_dsa(int    argc,
         ret |= test_oap_truncated_request();
 #else
         (void) test_oap_roundtrip_auth_only;
+        (void) test_oap_cli_md_pin_exempts_pqc;
+        (void) test_oap_srv_md_pin_exempts_pqc;
         (void) test_oap_roundtrip_kem;
         (void) test_oap_roundtrip_kem_all;
         (void) test_oap_kem_srv_uncfg;