TLS: improve support for "delegated_credentials" extension

Client support was added in bd597dc247.
Now, add decoding of the messages sent by the server.

See: https://www.ietf.org/archive/id/draft-ietf-tls-subcerts-10.txt

2 files changed, 91 insertions, 6 deletions

diff --git a/epan/dissectors/packet-tls-utils.c b/epan/dissectors/packet-tls-utils.c
index c34c67b613..e1ee76e54d 100644
--- a/epan/dissectors/packet-tls-utils.c
+++ b/epan/dissectors/packet-tls-utils.c
@@ -1195,7 +1195,7 @@ const value_string tls_hello_extension_types[] = {
     { SSL_HND_HELLO_EXT_CACHED_INFO, "cached_info" }, /* RFC 7924 */
     { SSL_HND_HELLO_EXT_COMPRESS_CERTIFICATE, "compress_certificate" }, /* https://tools.ietf.org/html/draft-ietf-tls-certificate-compression-03 */
     { SSL_HND_HELLO_EXT_RECORD_SIZE_LIMIT, "record_size_limit" }, /* RFC 8449 */
-    { SSL_HND_HELLO_EXT_DELEGATED_CREDENTIALS, "delegated_credentials" }, /* draft-ietf-tls-subcerts-09.txt */
+    { SSL_HND_HELLO_EXT_DELEGATED_CREDENTIALS, "delegated_credentials" }, /* draft-ietf-tls-subcerts-10.txt */
     { SSL_HND_HELLO_EXT_SESSION_TICKET_TLS, "session_ticket" }, /* RFC 5077 / RFC 8447 */
     { SSL_HND_HELLO_EXT_KEY_SHARE_OLD, "Reserved (key_share)" }, /* https://tools.ietf.org/html/draft-ietf-tls-tls13-22 (removed in -23) */
     { SSL_HND_HELLO_EXT_PRE_SHARED_KEY, "pre_shared_key" }, /* RFC 8446 */
@@ -6671,9 +6671,64 @@ ssl_dissect_hnd_hello_ext_sig_hash_algs(ssl_common_dissect_t *hf, tvbuff_t *tvb,
 
 static gint
 ssl_dissect_hnd_ext_delegated_credentials(ssl_common_dissect_t *hf, tvbuff_t *tvb,
-                                          proto_tree *tree, packet_info* pinfo, guint32 offset, guint32 offset_end)
+                                          proto_tree *tree, packet_info* pinfo, guint32 offset, guint32 offset_end, guint8 hnd_type)
 {
-    return ssl_dissect_hash_alg_list(hf, tvb, tree, pinfo, offset, offset_end);
+    if (hnd_type == SSL_HND_CLIENT_HELLO) {
+        /*
+         *  struct {
+         *    SignatureScheme supported_signature_algorithm<2..2^16-2>;
+         *  } SignatureSchemeList;
+         */
+
+        return ssl_dissect_hash_alg_list(hf, tvb, tree, pinfo, offset, offset_end);
+    } else {
+        asn1_ctx_t asn1_ctx;
+        guint pubkey_length, sign_length;
+
+        /*
+         *  struct {
+         *    uint32 valid_time;
+         *    SignatureScheme expected_cert_verify_algorithm;
+         *    opaque ASN1_subjectPublicKeyInfo<1..2^24-1>;
+         *  } Credential;
+         *
+         *  struct {
+         *    Credential cred;
+         *    SignatureScheme algorithm;
+         *    opaque signature<0..2^16-1>;
+         *  } DelegatedCredential;
+         */
+
+        asn1_ctx_init(&asn1_ctx, ASN1_ENC_BER, TRUE, pinfo);
+
+        proto_tree_add_item(tree, hf->hf.hs_cred_valid_time, tvb, offset, 4, ENC_BIG_ENDIAN);
+        offset += 4;
+
+        tls_dissect_signature_algorithm(hf, tvb, tree, offset);
+        offset += 2;
+
+        if (!ssl_add_vector(hf, tvb, pinfo, tree, offset, offset_end, &pubkey_length,
+                            hf->hf.hs_cred_pubkey_len, 1, G_MAXUINT24)) {
+            return offset_end;
+        }
+        offset += 3;
+        dissect_x509af_SubjectPublicKeyInfo(FALSE, tvb, offset, &asn1_ctx, tree, hf->hf.hs_cred_pubkey);
+        offset += pubkey_length;
+
+        tls_dissect_signature_algorithm(hf, tvb, tree, offset);
+        offset += 2;
+
+        if (!ssl_add_vector(hf, tvb, pinfo, tree, offset, offset_end, &sign_length,
+                            hf->hf.hs_cred_signature_len, 1, G_MAXUINT16)) {
+            return offset_end;
+        }
+        offset += 2;
+        proto_tree_add_item(tree, hf->hf.hs_cred_signature,
+                            tvb, offset, sign_length, ENC_ASCII|ENC_NA);
+        offset += sign_length;
+
+        return offset;
+    }
 }
 
 static gint
@@ -9512,7 +9567,7 @@ ssl_dissect_hnd_extension(ssl_common_dissect_t *hf, tvbuff_t *tvb, proto_tree *t
             offset = ssl_dissect_hnd_hello_ext_sig_hash_algs(hf, tvb, ext_tree, pinfo, offset, next_offset);
             break;
         case SSL_HND_HELLO_EXT_DELEGATED_CREDENTIALS:
-            offset = ssl_dissect_hnd_ext_delegated_credentials(hf, tvb, ext_tree, pinfo, offset, next_offset);
+            offset = ssl_dissect_hnd_ext_delegated_credentials(hf, tvb, ext_tree, pinfo, offset, next_offset, hnd_type);
             break;
         case SSL_HND_HELLO_EXT_USE_SRTP:
             if (is_dtls) {
diff --git a/epan/dissectors/packet-tls-utils.h b/epan/dissectors/packet-tls-utils.h
index 799632020b..699658245b 100644
--- a/epan/dissectors/packet-tls-utils.h
+++ b/epan/dissectors/packet-tls-utils.h
@@ -108,7 +108,7 @@ typedef enum {
 #define SSL_HND_HELLO_EXT_COMPRESS_CERTIFICATE          27
 #define SSL_HND_HELLO_EXT_RECORD_SIZE_LIMIT             28
 /* 26-33  Unassigned*/
-#define SSL_HND_HELLO_EXT_DELEGATED_CREDENTIALS         34 /* draft-ietf-tls-subcerts-09.txt */
+#define SSL_HND_HELLO_EXT_DELEGATED_CREDENTIALS         34 /* draft-ietf-tls-subcerts-10.txt */
 #define SSL_HND_HELLO_EXT_SESSION_TICKET_TLS            35
 /* RFC 8446 (TLS 1.3) */
 #define SSL_HND_HELLO_EXT_KEY_SHARE_OLD                 40 /* draft-ietf-tls-tls13-22 (removed in -23) */
@@ -966,6 +966,11 @@ typedef struct ssl_common_dissect {
         gint hs_ext_oid_filters_oid_length;
         gint hs_ext_oid_filters_oid;
         gint hs_ext_oid_filters_values_length;
+        gint hs_cred_valid_time;
+        gint hs_cred_pubkey;
+        gint hs_cred_pubkey_len;
+        gint hs_cred_signature;
+        gint hs_cred_signature_len;
 
         /* compress_certificate */
         gint hs_ext_compress_certificate_algorithms_length;
@@ -1269,7 +1274,7 @@ ssl_common_dissect_t name = {   \
         -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, \
         -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, \
         -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, \
-        -1, -1, -1, -1                                                  \
+        -1, -1, -1, -1, -1, -1, -1, -1, -1                              \
     },                                                                  \
     /* ett */ {                                                         \
         -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, \
@@ -2070,6 +2075,31 @@ ssl_common_dissect_t name = {   \
         FT_UINT16, BASE_DEC, NULL, 0x00,                                \
         NULL, HFILL }                                                   \
     },                                                                  \
+    { & name .hf.hs_cred_valid_time,                                    \
+      { "Valid Time", prefix ".handshake.cred.valid_time",              \
+        FT_UINT16, BASE_DEC, NULL, 0x0,                                 \
+        "Delegated Credentials Valid Time", HFILL }                     \
+    },                                                                  \
+    { & name .hf.hs_cred_pubkey,                                        \
+      { "Subject Public Key Info", prefix ".handshake.cred.pubkey",     \
+        FT_BYTES, BASE_NONE, NULL, 0x0,                                 \
+        "Delegated Credentials Subject Public Key Info", HFILL }        \
+    },                                                                  \
+    { & name .hf.hs_cred_pubkey_len,                                    \
+      { "Subject Public Key Info Length", prefix ".handshake.cred.pubkey_len", \
+        FT_UINT24, BASE_DEC, NULL, 0x0,                                 \
+        "Delegated Credentials Subject Public Key Info Length", HFILL } \
+    },                                                                  \
+    { & name .hf.hs_cred_signature,                                     \
+      { "Signature", prefix ".handshake.cred.signature",                \
+        FT_BYTES, BASE_NONE, NULL, 0x0,                                 \
+        "Delegated Credentials Signature", HFILL }                      \
+    },                                                                  \
+    { & name .hf.hs_cred_signature_len,                                 \
+      { "Signature Length", prefix ".handshake.cred.signature_len",     \
+        FT_UINT16, BASE_DEC, NULL, 0x0,                                 \
+        "Delegated Credentials Signature Length", HFILL }               \
+    },                                                                  \
     { & name .hf.hs_ext_compress_certificate_algorithms_length,         \
       { "Algorithms Length", prefix ".compress_certificate.algorithms_length", \
         FT_UINT8, BASE_DEC, NULL, 0x00,                                 \