diff options
| author | Nick Mathewson <nickm@torproject.org> | 2013-10-20 15:03:24 -0700 |
|---|---|---|
| committer | Ben Laurie <ben@links.org> | 2013-10-21 03:37:20 +0100 |
| commit | 2016265dfbab162ec30718b5e7480add42598158 (patch) | |
| tree | 9025eb6e5e30a9f6cd914b06cadbe11d9646d130 /ssl/s23_clnt.c | |
| parent | f3efeaad540b000779277b4fc49a239529ee616e (diff) | |
Do not include a timestamp in the Client/ServerHello Random field.
Instead, send random bytes, unless SSL_SEND_{CLIENT,SERVER}RANDOM_MODE
is set.
This is a forward-port of commits:
4af793036f6ef4f0a1078e5d7155426a98d50e37
f4c93b46edb51da71f09eda99e83eaf193a33c08
3da721dac9382c48812c8eba455528fd59af2eef
2583270191a8b27eed303c03ece1da97b9b69fd3
While the gmt_unix_time record was added in an ostensible attempt to
mitigate the dangers of a bad RNG, its presence leaks the host's view
of the current time in the clear. This minor leak can help
fingerprint TLS instances across networks and protocols... and what's
worse, it's doubtful thet the gmt_unix_time record does any good at
all for its intended purpose, since:
* It's quite possible to open two TLS connections in one second.
* If the PRNG output is prone to repeat itself, ephemeral
handshakes (and who knows what else besides) are broken.
Diffstat (limited to 'ssl/s23_clnt.c')
| -rw-r--r-- | ssl/s23_clnt.c | 26 |
1 files changed, 23 insertions, 3 deletions
diff --git a/ssl/s23_clnt.c b/ssl/s23_clnt.c index 15878c66e1..af4fffe67d 100644 --- a/ssl/s23_clnt.c +++ b/ssl/s23_clnt.c @@ -269,6 +269,28 @@ static int ssl23_no_ssl2_ciphers(SSL *s) return 1; } +/* Fill a ClientRandom or ServerRandom field of length len. Returns <= 0 + * on failure, 1 on success. */ +int ssl_fill_hello_random(SSL *s, int server, unsigned char *result, int len) + { + int send_time = 0; + if (len < 4) + return 0; + if (server) + send_time = (s->mode & SSL_MODE_SEND_SERVERHELLO_TIME) != 0; + else + send_time = (s->mode & SSL_MODE_SEND_CLIENTHELLO_TIME) != 0; + if (send_time) + { + unsigned long Time = time(NULL); + unsigned char *p = result; + l2n(Time, p); + return RAND_pseudo_bytes(p, len-4); + } + else + return RAND_pseudo_bytes(result, len); + } + static int ssl23_client_hello(SSL *s) { unsigned char *buf; @@ -359,9 +381,7 @@ static int ssl23_client_hello(SSL *s) #endif p=s->s3->client_random; - Time=(unsigned long)time(NULL); /* Time */ - l2n(Time,p); - if (RAND_pseudo_bytes(p,SSL3_RANDOM_SIZE-4) <= 0) + if (ssl_fill_hello_random(s, 0, p, SSL3_RANDOM_SIZE) <= 0) return -1; if (version == TLS1_2_VERSION) |