irmd: Specify peer authentication contract

OAP accepted requests and responses without a certificate even when
the peer was expected to authenticate. An on-path attacker could
strip the certificate and signature from a flow allocation response
and substitute its own key exchange, silently downgrading the
handshake to unauthenticated.

Add an auth=required|optional policy to enc.conf, enforced per role: a
client config requires the server to present a valid certificate, a
server config requires the same from the client. Default is required
for client side (https), optional server side. The client side default
can be changed via OAP_CLIENT_AUTH_DEFAULT for testing.

Replace the bare 'none' keyword with encryption=none, which disables
encryption only: the digest and the authentication policy are kept, so
authenticated but unencrypted flows can be configured. Configs using
bare 'none' are now rejected.

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

7 files changed, 155 insertions, 2 deletions

diff --git a/src/irmd/config.h.in b/src/irmd/config.h.in
index df0cd718..0364e080 100644
--- a/src/irmd/config.h.in
+++ b/src/irmd/config.h.in
@@ -42,6 +42,7 @@
 #define FLOW_DEALLOC_TIMEOUT   @FLOW_DEALLOC_TIMEOUT@
 
 #define OAP_REPLAY_TIMER       @OAP_REPLAY_TIMER@
+#cmakedefine01 OAP_CLIENT_AUTH_DEFAULT
 
 #define BOOTSTRAP_TIMEOUT      @BOOTSTRAP_TIMEOUT@
 #define ENROLL_TIMEOUT         @ENROLL_TIMEOUT@
diff --git a/src/irmd/oap/cli.c b/src/irmd/oap/cli.c
index 7a202da7..d38f38dd 100644
--- a/src/irmd/oap/cli.c
+++ b/src/irmd/oap/cli.c
@@ -93,6 +93,11 @@ int load_cli_kex_config(const struct name_info * info,
         assert(info != NULL);
         assert(cfg != NULL);
 
+        memset(cfg, 0, sizeof(*cfg));
+
+        /* A client authenticates the server by default, like an https client */
+        cfg->req_auth = OAP_CLIENT_AUTH_DEFAULT;
+
         return load_kex_config(info->name, info->c.enc, cfg);
 }
 
@@ -534,6 +539,12 @@ int oap_cli_complete(void *                   ctx,
                 goto fail_oap;
         }
 
+        /* Required peer auth makes sig and name binding mandatory */
+        if (s->kcfg.req_auth && peer_hdr.crt.len == 0) {
+                log_err_id(id, "Server did not provide a certificate.");
+                goto fail_oap;
+        }
+
         /* Verify request hash in authenticated response */
         if (peer_hdr.req_hash.len == 0) {
                 log_err_id(id, "Response missing req_hash.");
diff --git a/src/irmd/oap/io.c b/src/irmd/oap/io.c
index c2c91b91..24d33e60 100644
--- a/src/irmd/oap/io.c
+++ b/src/irmd/oap/io.c
@@ -103,8 +103,6 @@ int load_kex_config(const char *        name,
         assert(name != NULL);
         assert(cfg != NULL);
 
-        memset(cfg, 0, sizeof(*cfg));
-
         /* Load encryption config */
         if (!file_exists(path))
                 log_dbg("No encryption %s for %s.", path, name);
diff --git a/src/irmd/oap/srv.c b/src/irmd/oap/srv.c
index 587a8f9f..08b4d9d2 100644
--- a/src/irmd/oap/srv.c
+++ b/src/irmd/oap/srv.c
@@ -73,6 +73,9 @@ int load_srv_kex_config(const struct name_info * info,
         assert(info != NULL);
         assert(cfg != NULL);
 
+        memset(cfg, 0, sizeof(*cfg));
+
+        /* Client auth stays opt-in (mTLS); enable with auth=required */
         return load_kex_config(info->name, info->s.enc, cfg);
 }
 
@@ -441,6 +444,11 @@ int oap_srv_process(const struct name_info * info,
                 goto fail_auth;
         }
 
+        if (kcfg.req_auth && peer_hdr.crt.len == 0) {
+                log_err_id(id, "Client did not provide a certificate.");
+                goto fail_auth;
+        }
+
         if (do_server_kex(info, &peer_hdr, &kcfg, &local_hdr.kex, sk) < 0)
                 goto fail_kex;
 
diff --git a/src/irmd/oap/tests/common.c b/src/irmd/oap/tests/common.c
index 0a1af100..c5000e48 100644
--- a/src/irmd/oap/tests/common.c
+++ b/src/irmd/oap/tests/common.c
@@ -36,6 +36,8 @@ int load_srv_kex_config(const struct name_info * info,
 
         memset(cfg, 0, sizeof(*cfg));
 
+        cfg->req_auth = test_cfg.srv.req_auth;
+
         if (test_cfg.srv.kex == NID_undef)
                 return 0;
 
@@ -55,6 +57,8 @@ int load_cli_kex_config(const struct name_info * info,
 
         memset(cfg, 0, sizeof(*cfg));
 
+        cfg->req_auth = test_cfg.cli.req_auth;
+
         if (test_cfg.cli.kex == NID_undef)
                 return 0;
 
diff --git a/src/irmd/oap/tests/common.h b/src/irmd/oap/tests/common.h
index d4b6733a..fa500ffe 100644
--- a/src/irmd/oap/tests/common.h
+++ b/src/irmd/oap/tests/common.h
@@ -38,6 +38,7 @@ struct test_sec_cfg {
         int  md;        /* Digest NID for signatures */
         int  kem_mode;  /* KEM encapsulation mode (0 for ECDH) */
         bool auth;      /* Use authentication (certificates) */
+        bool req_auth;  /* Require peer authentication */
 };
 
 /* Test configuration - set by each test before running roundtrip */
diff --git a/src/irmd/oap/tests/oap_test.c b/src/irmd/oap/tests/oap_test.c
index a525d988..fd2c5629 100644
--- a/src/irmd/oap/tests/oap_test.c
+++ b/src/irmd/oap/tests/oap_test.c
@@ -1183,6 +1183,129 @@ static int test_oap_server_name_mismatch(void)
         return TEST_RC_FAIL;
 }
 
+/* Client requiring auth rejects a response without certificate */
+static int test_oap_cli_requires_srv_auth(void)
+{
+        struct oap_test_ctx ctx;
+
+        test_default_cfg();
+        test_cfg.srv.auth     = NO_AUTH;
+        test_cfg.cli.req_auth = true;
+
+        TEST_START();
+
+        if (oap_test_setup(&ctx, root_ca_crt_ec, im_ca_crt_ec) < 0)
+                goto fail;
+
+        if (oap_cli_prepare_ctx(&ctx) < 0) {
+                printf("Client prepare failed.\n");
+                goto fail_cleanup;
+        }
+
+        if (oap_srv_process_ctx(&ctx) < 0) {
+                printf("Server process failed.\n");
+                goto fail_cleanup;
+        }
+
+        if (oap_cli_complete_ctx(&ctx) == 0) {
+                printf("Client should reject unauthenticated server.\n");
+                goto fail_cleanup;
+        }
+
+        oap_test_teardown(&ctx);
+
+        TEST_SUCCESS();
+        return TEST_RC_SUCCESS;
+
+ fail_cleanup:
+        oap_test_teardown(&ctx);
+ fail:
+        TEST_FAIL();
+        return TEST_RC_FAIL;
+}
+
+/* Server requiring auth rejects a request without certificate */
+static int test_oap_srv_requires_cli_auth(void)
+{
+        struct oap_test_ctx ctx;
+
+        test_default_cfg();
+        test_cfg.srv.req_auth = true;
+
+        TEST_START();
+
+        if (oap_test_setup(&ctx, root_ca_crt_ec, im_ca_crt_ec) < 0)
+                goto fail;
+
+        if (oap_cli_prepare_ctx(&ctx) < 0) {
+                printf("Client prepare failed.\n");
+                goto fail_cleanup;
+        }
+
+        if (oap_srv_process_ctx(&ctx) == 0) {
+                printf("Server should reject unauthenticated client.\n");
+                goto fail_cleanup;
+        }
+
+        oap_test_teardown(&ctx);
+
+        TEST_SUCCESS();
+        return TEST_RC_SUCCESS;
+
+ fail_cleanup:
+        oap_test_teardown(&ctx);
+ fail:
+        TEST_FAIL();
+        return TEST_RC_FAIL;
+}
+
+/* Roundtrip succeeds when both sides require and provide auth */
+static int test_oap_mutual_req_auth(void)
+{
+        struct oap_test_ctx ctx;
+
+        test_default_cfg();
+        test_cfg.srv.req_auth = true;
+        test_cfg.cli.auth     = AUTH;
+        test_cfg.cli.req_auth = true;
+
+        TEST_START();
+
+        if (oap_test_setup(&ctx, root_ca_crt_ec, im_ca_crt_ec) < 0)
+                goto fail;
+
+        if (oap_cli_prepare_ctx(&ctx) < 0) {
+                printf("Client prepare failed.\n");
+                goto fail_cleanup;
+        }
+
+        if (oap_srv_process_ctx(&ctx) < 0) {
+                printf("Server process failed.\n");
+                goto fail_cleanup;
+        }
+
+        if (oap_cli_complete_ctx(&ctx) < 0) {
+                printf("Client complete failed.\n");
+                goto fail_cleanup;
+        }
+
+        if (memcmp(ctx.cli.key, ctx.srv.key, SYMMKEYSZ) != 0) {
+                printf("Client and server keys do not match!\n");
+                goto fail_cleanup;
+        }
+
+        oap_test_teardown(&ctx);
+
+        TEST_SUCCESS();
+        return TEST_RC_SUCCESS;
+
+ fail_cleanup:
+        oap_test_teardown(&ctx);
+ fail:
+        TEST_FAIL();
+        return TEST_RC_FAIL;
+}
+
 int oap_test(int    argc,
              char **argv)
 {
@@ -1220,6 +1343,10 @@ int oap_test(int    argc,
         ret |= test_oap_replay_packet();
         ret |= test_oap_missing_root_ca();
         ret |= test_oap_server_name_mismatch();
+
+        ret |= test_oap_cli_requires_srv_auth();
+        ret |= test_oap_srv_requires_cli_auth();
+        ret |= test_oap_mutual_req_auth();
 #else
         (void) test_oap_roundtrip_auth_only;
         (void) test_oap_roundtrip_kex_only;
@@ -1245,6 +1372,9 @@ int oap_test(int    argc,
         (void) test_oap_replay_packet;
         (void) test_oap_missing_root_ca;
         (void) test_oap_server_name_mismatch;
+        (void) test_oap_cli_requires_srv_auth;
+        (void) test_oap_srv_requires_cli_auth;
+        (void) test_oap_mutual_req_auth;
 
         ret = TEST_RC_SKIP;
 #endif