tls: in AES-CBC code, do not set key for every record - do it once

function                                             old     new   delta
aes_setkey                                            16     212    +196
tls_handshake                                       1941    1977     +36
aes_encrypt_1                                        382     396     +14
xwrite_encrypted                                     605     604      -1
tls_xread_record                                     659     656      -3
aes_encrypt_one_block                                 65      59      -6
aes_cbc_encrypt                                      172     121     -51
aesgcm_setkey                                         58       -     -58
aes_cbc_decrypt                                      958     881     -77
KeyExpansion                                         188       -    -188
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 3/5 up/down: 246/-384)         Total: -138 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/networking/tls.c b/networking/tls.c
index 38a965ad6..23622d76e 100644
--- a/networking/tls.c
+++ b/networking/tls.c
@@ -758,7 +758,7 @@ static void xwrite_encrypted_and_hmac_signed(tls_state_t *tls, unsigned size, un
         /* Encrypt content+MAC+padding in place */
 //optimize key setup
         aes_cbc_encrypt(
-                tls->client_write_key, tls->key_size, /* selects 128/256 */
+                &tls->aes_decrypt, /* selects 128/256 */
                 buf - AES_BLOCK_SIZE, /* IV */
                 buf, size, /* plaintext */
                 buf /* ciphertext */
@@ -1061,7 +1061,7 @@ static int tls_xread_record(tls_state_t *tls, const char *expected)
                         /* Decrypt content+MAC+padding, moving it over IV in the process */
                         sz -= AES_BLOCK_SIZE; /* we will overwrite IV now */
                         aes_cbc_decrypt(
-                                tls->server_write_key, tls->key_size, /* selects 128/256 */
+                                &tls->aes_decrypt, /* selects 128/256 */
                                 p, /* IV */
                                 p + AES_BLOCK_SIZE, sz, /* ciphertext */
                                 p /* plaintext */
@@ -1934,8 +1934,14 @@ static void send_client_key_exchange(tls_state_t *tls)
                 dump_hex("client_write_IV:%s\n",
                         tls->client_write_IV, tls->IV_size
                 );
-                aesgcm_setkey(tls->H, &tls->aes_encrypt, tls->client_write_key, tls->key_size);
+
                 aes_setkey(&tls->aes_decrypt, tls->server_write_key, tls->key_size);
+                aes_setkey(&tls->aes_encrypt, tls->client_write_key, tls->key_size);
+                {
+                        uint8_t iv[AES_BLOCK_SIZE];
+                        memset(iv, 0, AES_BLOCK_SIZE);
+                        aes_encrypt_one_block(&tls->aes_encrypt, iv, tls->H);
+                }
         }
 }