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client: reject handshakes with DH parameters < 768 bits.

Browse source 
Since the client has no way of communicating her supported parameter
range to the server, connections to servers that choose weak DH will
simply fail.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
This commit is contained in:
Emilia Kasper 2015-05-19 12:05:22 +02:00
parent ff4de7dde9
commit 63830384e9
4 changed files with 20 additions and 7 deletions
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3
CHANGES
View file

@ -4,7 +4,8 @@
Changes between 1.0.1m and 1.0.1n [xx XXX xxxx]
*)
*) Reject DH handshakes with parameters shorter than 768 bits.
[Kurt Roeckx and Emilia Kasper]
Changes between 1.0.1l and 1.0.1m [19 Mar 2015]

22
ssl/s3_clnt.c
View file

@ -3295,23 +3295,33 @@ int ssl3_check_cert_and_algorithm(SSL *s)
}
#endif
#ifndef OPENSSL_NO_DH
if ((alg_k & SSL_kEDH) &&
!(has_bits(i, EVP_PK_DH | EVP_PKT_EXCH) || (dh != NULL))) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_MISSING_DH_KEY);
if ((alg_k & SSL_kEDH) && dh == NULL) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, ERR_R_INTERNAL_ERROR);
goto f_err;
} else if ((alg_k & SSL_kDHr) && !has_bits(i, EVP_PK_DH | EVP_PKS_RSA)) {
}
if ((alg_k & SSL_kDHr) && !has_bits(i, EVP_PK_DH | EVP_PKS_RSA)) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
SSL_R_MISSING_DH_RSA_CERT);
goto f_err;
}
# ifndef OPENSSL_NO_DSA
else if ((alg_k & SSL_kDHd) && !has_bits(i, EVP_PK_DH | EVP_PKS_DSA)) {
if ((alg_k & SSL_kDHd) && !has_bits(i, EVP_PK_DH | EVP_PKS_DSA)) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
SSL_R_MISSING_DH_DSA_CERT);
goto f_err;
}
# endif
#endif
/* Check DHE only: static DH not implemented. */
if (alg_k & SSL_kEDH) {
int dh_size = BN_num_bits(dh->p);
if ((!SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 768)
|| (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 512)) {
SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_DH_KEY_TOO_SMALL);
goto f_err;
}
}
#endif /* !OPENSSL_NO_DH */
if (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && !has_bits(i, EVP_PKT_EXP)) {
#ifndef OPENSSL_NO_RSA

1
ssl/ssl.h
View file

@ -2524,6 +2524,7 @@ void ERR_load_SSL_strings(void);
# define SSL_R_DATA_LENGTH_TOO_LONG 146
# define SSL_R_DECRYPTION_FAILED 147
# define SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC 281
# define SSL_R_DH_KEY_TOO_SMALL 372
# define SSL_R_DH_PUBLIC_VALUE_LENGTH_IS_WRONG 148
# define SSL_R_DIGEST_CHECK_FAILED 149
# define SSL_R_DTLS_MESSAGE_TOO_BIG 334

1
ssl/ssl_err.c
View file

@ -441,6 +441,7 @@ static ERR_STRING_DATA SSL_str_reasons[] = {
{ERR_REASON(SSL_R_DECRYPTION_FAILED), "decryption failed"},
{ERR_REASON(SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC),
"decryption failed or bad record mac"},
{ERR_REASON(SSL_R_DH_KEY_TOO_SMALL), "dh key too small"},
{ERR_REASON(SSL_R_DH_PUBLIC_VALUE_LENGTH_IS_WRONG),
"dh public value length is wrong"},
{ERR_REASON(SSL_R_DIGEST_CHECK_FAILED), "digest check failed"},