- /* 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. */
- }
+ /* should be RAND_bytes, but we cannot work around a failure. */
+ if (RAND_pseudo_bytes(rand_premaster_secret,
+ sizeof(rand_premaster_secret)) <= 0)
+ goto err;
+ decrypt_len = RSA_private_decrypt((int)n,p,p,rsa,RSA_PKCS1_PADDING);
+ ERR_clear_error();
+
+ /* decrypt_len should be SSL_MAX_MASTER_KEY_LENGTH.
+ * decrypt_good will be 0xff if so and zero otherwise. */
+ decrypt_good = constant_time_eq_int_8(decrypt_len, SSL_MAX_MASTER_KEY_LENGTH);
+
+ /* If the version in the decrypted pre-master secret is correct
+ * then version_good will be 0xff, otherwise it'll be zero.
+ * 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". Thus version checks
+ * are done in constant time and are treated like any other
+ * decryption error. */
+ version_good = constant_time_eq_8(p[0], (unsigned)(s->client_version>>8));
+ version_good &= constant_time_eq_8(p[1], (unsigned)(s->client_version&0xff));
+
+ /* The premaster secret must contain the same version number as
+ * the ClientHello to detect version rollback attacks
+ * (strangely, the protocol does not offer such protection for
+ * DH ciphersuites). However, buggy clients exist that send the
+ * negotiated protocol version instead if the server does not
+ * support the requested protocol version. If
+ * SSL_OP_TLS_ROLLBACK_BUG is set, tolerate such clients. */
+ if (s->options & SSL_OP_TLS_ROLLBACK_BUG)
+ {
+ unsigned char workaround_good;
+ workaround_good = constant_time_eq_8(p[0], (unsigned)(s->version>>8));
+ workaround_good &= constant_time_eq_8(p[1], (unsigned)(s->version&0xff));
+ version_good |= workaround_good;
+ }
+
+ /* Both decryption and version must be good for decrypt_good
+ * to remain non-zero (0xff). */
+ decrypt_good &= version_good;
+
+ /* Now copy rand_premaster_secret over p using
+ * decrypt_good_mask. */
+ for (i = 0; i < (int) sizeof(rand_premaster_secret); i++)
+ {
+ p[i] = constant_time_select_8(decrypt_good, p[i],
+ rand_premaster_secret[i]);