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, 11 insertions, 0 deletions

diff --git a/src/irmd/oap/io.c b/src/irmd/oap/io.c
index 24d33e60..5c560ea5 100644
--- a/src/irmd/oap/io.c
+++ b/src/irmd/oap/io.c
@@ -100,6 +100,8 @@ int load_kex_config(const char *        name,
                     const char *        path,
                     struct sec_config * cfg)
 {
+        void * pin;
+
         assert(name != NULL);
         assert(cfg != NULL);
 
@@ -112,6 +114,15 @@ int load_kex_config(const char *        name,
                 return -1;
         }
 
+        if (cfg->cacert[0] != '\0') {
+                if (crypt_load_crt_file(cfg->cacert, &pin) < 0) {
+                        log_err("Failed to load pinned CA %s for %s.",
+                                cfg->cacert, name);
+                        return -EAUTH;
+                }
+                crypt_free_crt(pin);
+        }
+
         if (!IS_KEX_ALGO_SET(cfg)) {
                 log_info("Key exchange not configured for %s.", name);
                 return 0;