Provide struct/functions for handling TLSv1.3 key shares.

Pull out the key share handling code and provide a clean/self contained
interface. This will make it easier to support groups other than X25519.

ok beck@ inoguchi@ tb@

1 files changed, 13 insertions, 8 deletions

diff --git a/lib/libssl/tls13_client.c b/lib/libssl/tls13_client.c
index 3c55be6e680..69e75558dc1 100644
--- a/lib/libssl/tls13_client.c
+++ b/lib/libssl/tls13_client.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_client.c,v 1.38 2020/01/29 17:03:58 jsing Exp $ */
+/* $OpenBSD: tls13_client.c,v 1.39 2020/01/30 17:09:23 jsing Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -52,6 +52,11 @@ tls13_client_init(struct tls13_ctx *ctx)
 	if (!tls1_transcript_init(s))
 		return 0;
 
+	if ((ctx->hs->key_share = tls13_key_share_new(NID_X25519)) == NULL)
+		return 0;
+	if (!tls13_key_share_generate(ctx->hs->key_share))
+		return 0;
+
 	arc4random_buf(s->s3->client_random, SSL3_RANDOM_SIZE);
 
 	return 1;
@@ -394,6 +399,7 @@ tls13_server_hello_recv(struct tls13_ctx *ctx, CBS *cbs)
 	struct tls13_secret context;
 	unsigned char buf[EVP_MAX_MD_SIZE];
 	uint8_t *shared_key = NULL;
+	size_t shared_key_len = 0;
 	size_t hash_len;
 	SSL *s = ctx->ssl;
 	int ret = 0;
@@ -406,14 +412,12 @@ tls13_server_hello_recv(struct tls13_ctx *ctx, CBS *cbs)
 		return 1;
 
 	/* XXX - handle other key share types. */
-	if (ctx->hs->x25519_peer_public == NULL) {
+	if (ctx->hs->key_share == NULL) {
 		/* XXX - alert. */
 		goto err;
 	}
-	if ((shared_key = malloc(X25519_KEY_LENGTH)) == NULL)
-		goto err;
-	if (!X25519(shared_key, ctx->hs->x25519_private,
-	    ctx->hs->x25519_peer_public))
+	if (!tls13_key_share_derive(ctx->hs->key_share, &shared_key,
+	    &shared_key_len))
 		goto err;
 
 	s->session->cipher = S3I(s)->hs.new_cipher;
@@ -443,7 +447,7 @@ tls13_server_hello_recv(struct tls13_ctx *ctx, CBS *cbs)
 
 	/* Handshake secrets. */
 	if (!tls13_derive_handshake_secrets(ctx->hs->secrets, shared_key,
-	    X25519_KEY_LENGTH, &context))
+	    shared_key_len, &context))
 		goto err;
 
 	tls13_record_layer_set_aead(ctx->rl, ctx->aead);
@@ -460,7 +464,8 @@ tls13_server_hello_recv(struct tls13_ctx *ctx, CBS *cbs)
 	ret = 1;
 
  err:
-	freezero(shared_key, X25519_KEY_LENGTH);
+	freezero(shared_key, shared_key_len);
+
 	return ret;
 }