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Don't disable rollback attack detection as a recommended bug workaround.

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This commit is contained in:
Lutz Jänicke 2001-08-03 08:45:13 +00:00
parent b72faddc47
commit 06da6e4977
3 changed files with 28 additions and 14 deletions
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8
CHANGES
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@ -12,6 +12,14 @@
*) applies to 0.9.6a/0.9.6b/0.9.6c and 0.9.7
+) applies to 0.9.7 only
+) Move SSL_OP_TLS_ROLLBACK_BUG out of the SSL_OP_ALL list of recommended
bug workarounds. Rollback attack detection is a security feature.
The problem will only arise on OpenSSL servers, when TLSv1 is not
available (sslv3_server_method() or SSL_OP_NO_TLSv1).
Software authors not wanting to support TLSv1 will have special reasons
for their choice and can explicitly enable this option.
[Bodo Moeller, Lutz Jaenicke]
+) Rationalise EVP so it can be extended: don't include a union of
cipher/digest structures, add init/cleanup functions. This also reduces
the number of header dependencies.

28
doc/ssl/SSL_CTX_set_options.pod
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@ -100,18 +100,6 @@ doing a re-connect, always takes the first cipher in the cipher list.
...
=item SSL_OP_TLS_ROLLBACK_BUG
Disable version rollback attack detection.
During the client key exchange, the client must send the same information
about acceptable SSL/TLS protocol levels as during the first hello. Some
clients violate this rule by adapting to the server's answer. (Example:
the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
only understands up to SSLv3. In this case the client must still use the
same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
to the server's answer and violate the version rollback protection.)
=item SSL_OP_ALL
All of the above bug workarounds.
@ -125,6 +113,18 @@ The following B<modifying> options are available:
=over 4
=item SSL_OP_TLS_ROLLBACK_BUG
Disable version rollback attack detection.
During the client key exchange, the client must send the same information
about acceptable SSL/TLS protocol levels as during the first hello. Some
clients violate this rule by adapting to the server's answer. (Example:
the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
only understands up to SSLv3. In this case the client must still use the
same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
to the server's answer and violate the version rollback protection.)
=item SSL_OP_SINGLE_DH_USE
Always create a new key when using temporary/ephemeral DH parameters
@ -207,6 +207,8 @@ L<dhparam(1)|dhparam(1)>
SSL_OP_CIPHER_SERVER_PREFERENCE has been added in OpenSSL 0.9.7.
SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6.
SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6 and was automatically
enabled with SSL_OP_ALL. As of 0.9.7 it is no longer included in SSL_OP_ALL
and must be explicitely set.
=cut

6
ssl/ssl.h
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@ -332,7 +332,6 @@ typedef struct ssl_session_st
#define SSL_OP_SSLEAY_080_CLIENT_DH_BUG 0x00000080L
#define SSL_OP_TLS_D5_BUG 0x00000100L
#define SSL_OP_TLS_BLOCK_PADDING_BUG 0x00000200L
#define SSL_OP_TLS_ROLLBACK_BUG 0x00000400L
/* If set, always create a new key when using tmp_dh parameters */
#define SSL_OP_SINGLE_DH_USE 0x00100000L
@ -341,6 +340,11 @@ typedef struct ssl_session_st
/* Set on servers to choose the cipher according to the server's
* preferences */
#define SSL_OP_CIPHER_SERVER_PREFERENCE 0x00400000L
/* If set, a server will allow a client to issue a SSLv3.0 version number
* as latest version supported in the premaster secret, even when TLSv1.0
* (version 3.1) was announced in the client hello. Normally this is
* forbidden to prevent version rollback attacks. */
#define SSL_OP_TLS_ROLLBACK_BUG 0x00800000L
/* The next flag deliberately changes the ciphertest, this is a check
* for the PKCS#1 attack */