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Prefer SHA-256 ciphersuites if using old style PSKs

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If we have no certificate and we are using "old style" PSKs then we will
always default to using SHA-256 for that PSK. However we may have selected
a ciphersuite that is not based on SHA-256. Therefore if we see that there
are no certificates and we have been configured for "old style" PSKs then
we should prefer SHA-256 based ciphersuites during the selection process.

Fixes 

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6215)
This commit is contained in:
Matt Caswell 2018-05-10 11:51:45 +01:00
parent 3cb7c5cfef
commit 48a03162db
1 changed files with 31 additions and 2 deletions

33
ssl/s3_lib.c

@ -4108,8 +4108,9 @@ const SSL_CIPHER *ssl3_choose_cipher(SSL *s, STACK_OF(SSL_CIPHER) *clnt,
{
const SSL_CIPHER *c, *ret = NULL;
STACK_OF(SSL_CIPHER) *prio, *allow;
int i, ii, ok;
int i, ii, ok, prefer_sha256 = 0;
unsigned long alg_k = 0, alg_a = 0, mask_k = 0, mask_a = 0;
const EVP_MD *mdsha256 = EVP_sha256();
#ifndef OPENSSL_NO_CHACHA
STACK_OF(SSL_CIPHER) *prio_chacha = NULL;
#endif
@ -4190,7 +4191,24 @@ const SSL_CIPHER *ssl3_choose_cipher(SSL *s, STACK_OF(SSL_CIPHER) *clnt,
allow = srvr;
}
if (!SSL_IS_TLS13(s)) {
if (SSL_IS_TLS13(s)) {
int j;
/*
* If we allow "old" style PSK callbacks, and we have no certificate (so
* we're not going to succeed without a PSK anyway), and we're in
* TLSv1.3 then the default hash for a PSK is SHA-256 (as per the
* TLSv1.3 spec). Therefore we should prioritise ciphersuites using
* that.
*/
if (s->psk_server_callback != NULL) {
for (j = 0; j < SSL_PKEY_NUM && !ssl_has_cert(s, j); j++);
if (j == SSL_PKEY_NUM) {
/* There are no certificates */
prefer_sha256 = 1;
}
}
} else {
tls1_set_cert_validity(s);
ssl_set_masks(s);
}
@ -4262,6 +4280,17 @@ const SSL_CIPHER *ssl3_choose_cipher(SSL *s, STACK_OF(SSL_CIPHER) *clnt,
continue;
}
#endif
if (prefer_sha256) {
const SSL_CIPHER *tmp = sk_SSL_CIPHER_value(allow, ii);
if (ssl_md(tmp->algorithm2) == mdsha256) {
ret = tmp;
break;
}
if (ret == NULL)
ret = tmp;
continue;
}
ret = sk_SSL_CIPHER_value(allow, ii);
break;
}