Implement parsing and processing of TLSv1.3 ServerHello messages.

ok tb@

1 files changed, 178 insertions, 1 deletions

diff --git a/src/lib/libssl/tls13_client.c b/src/lib/libssl/tls13_client.c
index 1a2529be6a..4d34cf9943 100644
--- a/src/lib/libssl/tls13_client.c
+++ b/src/lib/libssl/tls13_client.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_client.c,v 1.1 2019/01/21 13:45:57 jsing Exp $ */
+/* $OpenBSD: tls13_client.c,v 1.2 2019/02/04 16:18:15 jsing Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -22,6 +22,7 @@
 
 #include "bytestring.h"
 #include "ssl_tlsext.h"
+#include "tls13_handshake.h"
 #include "tls13_internal.h"
 
 int
@@ -137,3 +138,179 @@ tls13_client_hello_send(struct tls13_ctx *ctx)
 
         return 1;
 }
+
+/*
+ * HelloRetryRequest hash - RFC 8446 section 4.1.3.
+ */
+static const uint8_t tls13_hello_retry_request_hash[] = {
+        0xcf, 0x21, 0xad, 0x74, 0xe5, 0x9a, 0x61, 0x11,
+        0xbe, 0x1d, 0x8c, 0x02, 0x1e, 0x65, 0xb8, 0x91,
+        0xc2, 0xa2, 0x11, 0x16, 0x7a, 0xbb, 0x8c, 0x5e,
+        0x07, 0x9e, 0x09, 0xe2, 0xc8, 0xa8, 0x33, 0x9c, 
+};
+
+static int
+tls13_server_hello_process(struct tls13_ctx *ctx, CBS *cbs)
+{
+        CBS server_random, session_id;
+        uint16_t cipher_suite, legacy_version;
+        uint8_t compression_method;
+        const SSL_CIPHER *cipher;
+        SSL *s = ctx->ssl;
+        int alert;
+
+        if (!CBS_get_u16(cbs, &legacy_version))
+                goto err;
+        if (!CBS_get_bytes(cbs, &server_random, SSL3_RANDOM_SIZE))
+                goto err;
+        if (!CBS_get_u8_length_prefixed(cbs, &session_id))
+                goto err;
+        if (!CBS_get_u16(cbs, &cipher_suite))
+                goto err;
+        if (!CBS_get_u8(cbs, &compression_method))
+                goto err;
+
+        if (!tlsext_client_parse(s, cbs, &alert, SSL_TLSEXT_MSG_SH))
+                goto err;
+
+        if (CBS_len(cbs) != 0)
+                goto err;
+
+        /*
+         * See if a supported versions extension was returned. If it was then
+         * the legacy version must be set to 0x0303 (RFC 8446 section 4.1.3).
+         * Otherwise, fallback to the legacy version, ensuring that it is both
+         * within range and not TLS 1.3 or greater (which must use the
+         * supported version extension.
+         */
+        if (S3I(s)->hs_tls13.server_version != 0) {
+                if (legacy_version != TLS1_2_VERSION) {
+                        /* XXX - alert. */
+                        goto err;
+                }
+        } else {
+                if (legacy_version < S3I(s)->hs_tls13.min_version ||
+                    legacy_version > S3I(s)->hs_tls13.max_version ||
+                    legacy_version > TLS1_2_VERSION) {
+                        /* XXX - alert. */
+                        goto err;
+                }
+                S3I(s)->hs_tls13.server_version = legacy_version;
+        }
+
+        /* XXX - session_id must match. */
+
+        /*
+         * Ensure that the cipher suite is one that we offered in the client
+         * hello and that it matches the TLS version selected.
+         */
+        cipher = ssl3_get_cipher_by_value(cipher_suite);
+        if (cipher == NULL ||
+            sk_SSL_CIPHER_find(ssl_get_ciphers_by_id(s), cipher) < 0) {
+                /* XXX - alert. */
+                goto err;
+        }
+        if (S3I(s)->hs_tls13.server_version == TLS1_3_VERSION &&
+            cipher->algorithm_ssl != SSL_TLSV1_3) {
+                /* XXX - alert. */
+                goto err;
+        }
+        /* XXX - move this to hs_tls13? */
+        S3I(s)->hs.new_cipher = cipher;
+
+        if (compression_method != 0) {
+                /* XXX - alert. */
+                goto err;
+        }
+
+        if (CBS_mem_equal(&server_random, tls13_hello_retry_request_hash,
+            sizeof(tls13_hello_retry_request_hash)))
+                ctx->handshake_stage.hs_type |= WITH_HRR;
+
+        return 1;
+
+ err:
+        return 0;
+}
+
+int
+tls13_server_hello_recv(struct tls13_ctx *ctx)
+{
+        struct tls13_secrets *secrets;
+        struct tls13_secret context;
+        unsigned char buf[EVP_MAX_MD_SIZE];
+        uint8_t *shared_key = NULL;
+        size_t hash_len;
+        SSL *s = ctx->ssl;
+        int ret = 0;
+        CBS cbs;
+
+        if (!tls13_handshake_msg_content(ctx->hs_msg, &cbs))
+                goto err;
+
+        if (!tls13_server_hello_process(ctx, &cbs))
+                goto err;
+
+        if (S3I(s)->hs_tls13.server_version < TLS1_3_VERSION) {
+                /* XXX - switch back to legacy client. */
+        }
+
+        if (ctx->handshake_stage.hs_type & WITH_HRR)
+                return 1;
+
+        /* XXX - handle other key share types. */
+        if (S3I(s)->hs_tls13.x25519_peer_public == NULL) {
+                /* XXX - alert. */
+                goto err;
+        }
+        if ((shared_key = malloc(X25519_KEY_LENGTH)) == NULL)
+                goto err;
+        if (!X25519(shared_key, S3I(s)->hs_tls13.x25519_private,
+            S3I(s)->hs_tls13.x25519_peer_public))
+                goto err;
+
+        s->session->cipher = S3I(s)->hs.new_cipher;
+        s->session->ssl_version = S3I(s)->hs_tls13.server_version;
+
+        if ((ctx->aead = tls13_cipher_aead(S3I(s)->hs.new_cipher)) == NULL)
+                goto err;
+        if ((ctx->hash = tls13_cipher_hash(S3I(s)->hs.new_cipher)) == NULL)
+                goto err;
+
+        if ((secrets = tls13_secrets_create(ctx->hash, 0)) == NULL)
+                goto err;
+        S3I(ctx->ssl)->hs_tls13.secrets = secrets;
+
+        /* XXX - pass in hash. */
+        if (!tls1_handshake_hash_init(s))
+                goto err;
+        if (!tls1_handshake_hash_value(s, buf, sizeof(buf), &hash_len))
+                goto err;
+        context.data = buf;
+        context.len = hash_len;
+
+        /* Early secrets. */
+        if (!tls13_derive_early_secrets(secrets, secrets->zeros.data,
+            secrets->zeros.len, &context))
+                goto err;
+
+        /* Handshake secrets. */
+        if (!tls13_derive_handshake_secrets(S3I(s)->hs_tls13.secrets,
+            shared_key, X25519_KEY_LENGTH, &context))
+                goto err;
+
+        tls13_record_layer_set_aead(ctx->rl, ctx->aead);
+        tls13_record_layer_set_hash(ctx->rl, ctx->hash);
+
+        if (!tls13_record_layer_set_traffic_keys(ctx->rl,
+            &secrets->server_handshake_traffic,
+            &secrets->client_handshake_traffic))
+                goto err;
+
+        ctx->handshake_stage.hs_type |= NEGOTIATED;
+        ret = 1;
+
+ err:
+        freezero(shared_key, X25519_KEY_LENGTH);
+        return ret;
+}