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tls: teach it to decrypt AES256-encrypted data

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This adds decryption only.
There is no MAC verification, code simply throws away MAC.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2017-01-19 00:20:45 +01:00
parent a9e1866806
commit cccf8e735d
1 changed files with 54 additions and 21 deletions
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75
networking/tls.c
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@ -181,7 +181,7 @@ typedef struct tls_state {
uint8_t master_secret[48];
uint8_t encrypt_on_write;
uint8_t decrypt_on_read;
int min_encrypted_len_on_read;
uint8_t client_write_MAC_key[SHA256_OUTSIZE];
uint8_t server_write_MAC_key[SHA256_OUTSIZE];
uint8_t client_write_key[AES256_KEYSIZE];
@ -634,7 +634,7 @@ static void xwrite_and_hash(tls_state_t *tls, /*const*/ void *buf, unsigned size
static int xread_tls_block(tls_state_t *tls)
{
struct record_hdr *xhdr;
int len;
int sz;
int total;
int target;
@ -658,24 +658,57 @@ static int xread_tls_block(tls_state_t *tls)
/* if total >= target, we have a full packet (and possibly more)... */
if (total - target >= 0)
break;
len = safe_read(tls->fd, tls->inbuf + total, sizeof(tls->inbuf) - total);
if (len <= 0)
sz = safe_read(tls->fd, tls->inbuf + total, sizeof(tls->inbuf) - total);
if (sz <= 0)
bb_perror_msg_and_die("short read");
total += len;
total += sz;
}
tls->tail = total - target;
tls->insize = target;
target -= sizeof(*xhdr);
sz = target - sizeof(*xhdr);
/* Needs to be decrypted? */
if (tls->min_encrypted_len_on_read) {
psCipherContext_t ctx;
uint8_t *p = tls->inbuf + sizeof(*xhdr);
int padding_len;
if (sz & (AES_BLOCKSIZE-1)
|| sz < tls->min_encrypted_len_on_read
) {
bb_error_msg_and_die("bad encrypted len:%u", sz);
}
/* Decrypt content+MAC+padding in place */
psAesInit(&ctx, p, /* IV */
tls->server_write_key, sizeof(tls->server_write_key)
);
psAesDecrypt(&ctx,
p + AES_BLOCKSIZE, /* ciphertext */
p + AES_BLOCKSIZE, /* plaintext */
sz
);
padding_len = p[sz - 1];
dbg("encrypted size:%u type:0x%02x padding_length:0x%02x\n", sz, p[AES_BLOCKSIZE], padding_len);
padding_len++;
sz -= AES_BLOCKSIZE + SHA256_OUTSIZE + padding_len;
if (sz < 0) {
bb_error_msg_and_die("bad padding size:%u", padding_len);
}
if (sz != 0) {
/* Skip IV */
memmove(tls->inbuf + 5, tls->inbuf + 5 + AES_BLOCKSIZE, sz);
}
}
/* RFC 5246 is not saying it explicitly, but sha256 hash
* in our FINISHED record must include data of incoming packets too!
*/
if (tls->inbuf[0] == RECORD_TYPE_HANDSHAKE) {
sha256_hash_dbg("<< sha256:%s", &tls->handshake_sha256_ctx, tls->inbuf + 5, target);
sha256_hash_dbg("<< sha256:%s", &tls->handshake_sha256_ctx, tls->inbuf + 5, sz);
}
dbg("got block len:%u\n", target);
return target;
dbg("got block len:%u\n", sz);
return sz;
}
/*
@ -1194,9 +1227,6 @@ static void send_change_cipher_spec(tls_state_t *tls)
/* Not "xwrite_and_hash": this is not a handshake message */
dbg(">> CHANGE_CIPHER_SPEC\n");
xwrite(tls->fd, rec_CHANGE_CIPHER_SPEC, sizeof(rec_CHANGE_CIPHER_SPEC));
/* tls->write_seq64_be = 0; - already is */
tls->encrypt_on_write = 1;
}
// 7.4.9. Finished
@ -1335,7 +1365,9 @@ static void tls_handshake(tls_state_t *tls)
send_client_key_exchange(tls);
send_change_cipher_spec(tls);
/* we now should send encrypted... as soon as we grok AES. */
/* from now on we should send encrypted */
/* tls->write_seq64_be = 0; - already is */
tls->encrypt_on_write = 1;
send_client_finished(tls);
@ -1344,8 +1376,8 @@ static void tls_handshake(tls_state_t *tls)
if (len != 1 || memcmp(tls->inbuf, rec_CHANGE_CIPHER_SPEC, 6) != 0)
tls_error_die(tls);
dbg("<< CHANGE_CIPHER_SPEC\n");
tls->decrypt_on_read = 1;
/* we now should receive encrypted */
/* all incoming packets now should be encrypted and have IV + MAC + padding */
tls->min_encrypted_len_on_read = AES_BLOCKSIZE + SHA256_OUTSIZE + AES_BLOCKSIZE;
/* Get (encrypted) FINISHED from the server */
len = xread_tls_block(tls);
@ -1356,8 +1388,13 @@ static void tls_handshake(tls_state_t *tls)
}
// To run a test server using openssl:
// openssl s_server -key key.pem -cert server.pem -debug -tls1_2 -no_tls1 -no_tls1_1
// openssl req -x509 -newkey rsa:$((4096/4*3)) -keyout key.pem -out server.pem -nodes -days 99999 -subj '/CN=localhost'
// openssl s_server -key key.pem -cert server.pem -debug -tls1_2 -no_tls1 -no_tls1_1
//
// Unencryped SHA256 example:
// openssl req -x509 -newkey rsa:$((4096/4*3)) -keyout key.pem -out server.pem -nodes -days 99999 -subj '/CN=localhost'
// openssl s_server -key key.pem -cert server.pem -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher NULL
// openssl s_client -connect 127.0.0.1:4433 -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher NULL-SHA256
int tls_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tls_main(int argc UNUSED_PARAM, char **argv)
@ -1381,12 +1418,8 @@ int tls_main(int argc UNUSED_PARAM, char **argv)
return EXIT_SUCCESS;
}
/* Unencryped SHA256 example:
* $ openssl req -x509 -newkey rsa:$((4096/4*3)) -keyout key.pem -out server.pem -nodes -days 99999 -subj '/CN=localhost'
* $ openssl s_server -key key.pem -cert server.pem -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher NULL
* $ openssl s_client -connect 127.0.0.1:4433 -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher NULL-SHA256
* s_client says:
* s_client says:
write to 0x1d750b0 [0x1e6f153] (99 bytes => 99 (0x63))
0000 - 16 03 01 005e 01 00005a 0303 [4d ef 5c 82 3e ....^...Z..M.\.> >> ClHello