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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 19:19:58 +00:00
parent 84b1e84af1
commit 409a5de586
2 changed files with 17 additions and 13 deletions
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6
CHANGES
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@ -4,6 +4,12 @@
Changes between 0.9.7a and 0.9.7b [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]
*) Turn on RSA blinding by default in the default implementation
to avoid a timing attack. Applications that don't want it can call
RSA_blinding_off() or use the new flag RSA_FLAG_NO_BLINDING.

24
ssl/s3_srvr.c
View file

@ -1447,7 +1447,7 @@ static int ssl3_get_client_key_exchange(SSL *s)
if (i != SSL_MAX_MASTER_KEY_LENGTH)
{
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))))
@ -1463,30 +1463,28 @@ static int ssl3_get_client_key_exchange(SSL *s)
(p[0] == (s->version>>8)) && (p[1] == (s->version & 0xff))))
{
al=SSL_AD_DECODE_ERROR;
SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_PROTOCOL_VERSION_NUMBER);
goto f_err;
/* SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_PROTOCOL_VERSION_NUMBER); */
/* 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 0
goto f_err;
#else
/* Some decryption failure -- use random value instead as countermeasure
* against Bleichenbacher's attack on PKCS #1 v1.5 RSA padding
* (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).
*/
* (see RFC 2246, section 7.4.7.1). */
ERR_clear_error();
i = SSL_MAX_MASTER_KEY_LENGTH;
p[0] = s->client_version >> 8;
p[1] = s->client_version & 0xff;
RAND_pseudo_bytes(p+2, i-2); /* should be RAND_bytes, but we cannot work around a failure */
#endif
}
s->session->master_key_length=