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countermeasure against new Klima-Pokorny-Rosa atack

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This commit is contained in:
Bodo Möller 2003-03-19 19:20:30 +00:00
parent 00223b969d
commit ef42d6a4ed
2 changed files with 16 additions and 14 deletions
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6
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@ -4,7 +4,11 @@
Changes between 0.9.6i and 0.9.6j [xx XXX 2003] Changes between 0.9.6i and 0.9.6j [xx XXX 2003]
*) *) Countermeasure against the Klima-Pokorny-Rosa extension of
Bleichbacher's attack on PKCS #1 v1.5 padding: treat
a protocol version number mismatch like a decryption error
in ssl3_get_client_key_exchange (ssl/s3_srvr.c).
[Bodo Moeller]
Changes between 0.9.6h and 0.9.6i [19 Feb 2003] Changes between 0.9.6h and 0.9.6i [19 Feb 2003]

24
ssl/s3_srvr.c
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@ -1425,7 +1425,7 @@ static int ssl3_get_client_key_exchange(SSL *s)
if (i != SSL_MAX_MASTER_KEY_LENGTH) if (i != SSL_MAX_MASTER_KEY_LENGTH)
{ {
al=SSL_AD_DECODE_ERROR; al=SSL_AD_DECODE_ERROR;
SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_RSA_DECRYPT); /* SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_RSA_DECRYPT); */
} }
if ((al == -1) && !((p[0] == (s->client_version>>8)) && (p[1] == (s->client_version & 0xff)))) if ((al == -1) && !((p[0] == (s->client_version>>8)) && (p[1] == (s->client_version & 0xff))))
@ -1441,30 +1441,28 @@ static int ssl3_get_client_key_exchange(SSL *s)
(p[0] == (s->version>>8)) && (p[1] == (s->version & 0xff)))) (p[0] == (s->version>>8)) && (p[1] == (s->version & 0xff))))
{ {
al=SSL_AD_DECODE_ERROR; al=SSL_AD_DECODE_ERROR;
SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_PROTOCOL_VERSION_NUMBER); /* SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_PROTOCOL_VERSION_NUMBER); */
goto f_err;
/* The Klima-Pokorny-Rosa extension of Bleichenbacher's attack
* (http://eprint.iacr.org/2003/052/) exploits the version
* number check as a "bad version oracle" -- an alert would
* reveal that the plaintext corresponding to some ciphertext
* made up by the adversary is properly formatted except
* that the version number is wrong. To avoid such attacks,
* we should treat this just like any other decryption error. */
} }
} }
if (al != -1) if (al != -1)
{ {
#if 0
goto f_err;
#else
/* Some decryption failure -- use random value instead as countermeasure /* Some decryption failure -- use random value instead as countermeasure
* against Bleichenbacher's attack on PKCS #1 v1.5 RSA padding * against Bleichenbacher's attack on PKCS #1 v1.5 RSA padding
* (see RFC 2246, section 7.4.7.1). * (see RFC 2246, section 7.4.7.1). */
* But note that due to length and protocol version checking, the
* attack is impractical anyway (see section 5 in D. Bleichenbacher:
* "Chosen Ciphertext Attacks Against Protocols Based on the RSA
* Encryption Standard PKCS #1", CRYPTO '98, LNCS 1462, pp. 1-12).
*/
ERR_clear_error(); ERR_clear_error();
i = SSL_MAX_MASTER_KEY_LENGTH; i = SSL_MAX_MASTER_KEY_LENGTH;
p[0] = s->client_version >> 8; p[0] = s->client_version >> 8;
p[1] = s->client_version & 0xff; p[1] = s->client_version & 0xff;
RAND_pseudo_bytes(p+2, i-2); /* should be RAND_bytes, but we cannot work around a failure */ RAND_pseudo_bytes(p+2, i-2); /* should be RAND_bytes, but we cannot work around a failure */
#endif
} }
s->session->master_key_length= s->session->master_key_length=