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-rw-r--r--src/protocols/ec25519_fhmqvc/handshake.c36
1 files changed, 22 insertions, 14 deletions
diff --git a/src/protocols/ec25519_fhmqvc/handshake.c b/src/protocols/ec25519_fhmqvc/handshake.c
index 2b676d8..a9fc1a2 100644
--- a/src/protocols/ec25519_fhmqvc/handshake.c
+++ b/src/protocols/ec25519_fhmqvc/handshake.c
@@ -50,6 +50,24 @@
#define RECORD_T RECORD_PROTOCOL5
+static void derive_key(fastd_sha256_t *out, size_t blocks, const uint32_t *salt, const char *method_name,
+ const aligned_int256_t *A, const aligned_int256_t *B, const aligned_int256_t *X, const aligned_int256_t *Y,
+ const aligned_int256_t *sigma) {
+ size_t methodlen = strlen(method_name);
+ uint8_t info[4*PUBLICKEYBYTES + methodlen];
+
+ memcpy(info, A->p, PUBLICKEYBYTES);
+ memcpy(info+PUBLICKEYBYTES, B->p, PUBLICKEYBYTES);
+ memcpy(info+2*PUBLICKEYBYTES, X->p, PUBLICKEYBYTES);
+ memcpy(info+3*PUBLICKEYBYTES, Y->p, PUBLICKEYBYTES);
+ memcpy(info+4*PUBLICKEYBYTES, method_name, methodlen);
+
+ fastd_sha256_t prk;
+ fastd_hkdf_sha256_extract(&prk, salt, (const uint32_t*)sigma->p, PUBLICKEYBYTES);
+
+ fastd_hkdf_sha256_expand(out, blocks, &prk, info, sizeof(info));
+}
+
static inline void supersede_session(fastd_context_t *ctx, fastd_peer_t *peer, const fastd_method_t *method) {
if (is_session_valid(ctx, &peer->protocol_state->session) && !is_session_valid(ctx, &peer->protocol_state->old_session)) {
if (peer->protocol_state->old_session.method)
@@ -80,21 +98,9 @@ static inline void new_session(fastd_context_t *ctx, fastd_peer_t *peer, const c
supersede_session(ctx, peer, method);
if (salt) {
- size_t methodlen = strlen(method_name);
- uint8_t info[4*PUBLICKEYBYTES + methodlen];
-
- memcpy(info, A->p, PUBLICKEYBYTES);
- memcpy(info+PUBLICKEYBYTES, B->p, PUBLICKEYBYTES);
- memcpy(info+2*PUBLICKEYBYTES, X->p, PUBLICKEYBYTES);
- memcpy(info+3*PUBLICKEYBYTES, Y->p, PUBLICKEYBYTES);
- memcpy(info+4*PUBLICKEYBYTES, method_name, methodlen);
-
- fastd_sha256_t prk;
- fastd_hkdf_sha256_extract(&prk, salt, (const uint32_t*)sigma->p, PUBLICKEYBYTES);
-
size_t blocks = block_count(method->key_length(ctx), sizeof(fastd_sha256_t));
fastd_sha256_t secret[blocks];
- fastd_hkdf_sha256_expand(secret, blocks, &prk, info, sizeof(info));
+ derive_key(secret, blocks, salt, method_name, A, B, X, Y, sigma);
peer->protocol_state->session.method_state = method->session_init(ctx, (const uint8_t*)secret, initiator);
}
@@ -165,6 +171,8 @@ static bool make_shared_handshake_key(fastd_context_t *ctx, const ecc_int256_t *
aligned_int256_t *sigma,
fastd_sha256_t *shared_handshake_key,
fastd_sha256_t *shared_handshake_key_compat) {
+ static const uint32_t zero_salt[FASTD_HMACSHA256_KEY_WORDS] = {};
+
ecc_25519_work_t work, workXY;
if (!ecc_25519_load_packed(&workXY, initiator ? Y : X))
@@ -212,7 +220,7 @@ static bool make_shared_handshake_key(fastd_context_t *ctx, const ecc_int256_t *
ecc_25519_store_packed(sigma, &work);
if (shared_handshake_key)
- fastd_sha256_blocks(shared_handshake_key, Y->p, X->p, B->p, A->p, sigma->p, NULL);
+ derive_key(shared_handshake_key, 1, zero_salt, "", A, B, X, Y, sigma);
if (shared_handshake_key_compat)
fastd_sha256_blocks(shared_handshake_key_compat, Y->p, X->p, B->p, A->p, sigma->p, NULL);