On Fri, May 01, 2015 at 04:51:03AM +0000, Viktor Dukhovni wrote:
> For this server, you need a more "compact" cipherlist as a work-around.
>
> smtp_tls_exclude_ciphers =
> #
> # Disable MD5, DSA, SRP and PSK, and the "exotic" fixed DH
> cipher suites.
> #
> MD5, SRP, PSK, aDSS, kECDH, kDH,
> #
> # Disable 256-bit ciphers, 128-bit is for now quite strong
> enough.
> # Also disable the largely unused SEED, IDEA, RC2, RC5, ...
> # leaving just AES128, CAMELLIA128, RC4 and 3DES.
> #
> AES256, CAMELLIA256, SEED, IDEA, RC2, RC5
Following up, we don't (as yet) even need to disable AES256 or
CAMELLIA256. Until ChaCha20 and other new cipher-suites show up,
the following still leaves RC4 in the top 64, and does not disable
anything useful in practice:
smtp_tls_exclude_ciphers =
#
# Disable MD5, DSA, SRP and PSK, and the "exotic" fixed DH
cipher suites.
#
MD5, SRP, PSK, aDSS, kECDH, kDH,
#
# Disable 256-bit ciphers, 128-bit is for now quite strong
enough.
# Also disable the largely unused SEED, IDEA, RC2, RC5, ...
# leaving just AES128, CAMELLIA128, RC4 and 3DES.
#
SEED, IDEA, RC2, RC5
This even with OpenSSL "master", which has more cipher-suites than older
releases:
$ openssl ciphers -v
'aNULL:-aNULL:HIGH:MEDIUM:LOW:EXPORT:+RC4:@STRENGTH:!kDH:!kECDH:!aDSS:!PSK:!SRP:!MD5:!SEED:!IDEA:!RC2:!RC5'
| egrep -n 'RC4-SHA|DES-CBC3-SHA'
49:AECDH-RC4-SHA SSLv3 Kx=ECDH Au=None Enc=RC4(128) Mac=SHA1
50:ECDHE-RSA-RC4-SHA SSLv3 Kx=ECDH Au=RSA Enc=RC4(128) Mac=SHA1
51:ECDHE-ECDSA-RC4-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=RC4(128) Mac=SHA1
52:RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1
53:AECDH-DES-CBC3-SHA SSLv3 Kx=ECDH Au=None Enc=3DES(168) Mac=SHA1
54:ADH-DES-CBC3-SHA SSLv3 Kx=DH Au=None Enc=3DES(168) Mac=SHA1
55:ECDHE-RSA-DES-CBC3-SHA SSLv3 Kx=ECDH Au=RSA Enc=3DES(168) Mac=SHA1
56:ECDHE-ECDSA-DES-CBC3-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=3DES(168)
Mac=SHA1
57:DHE-RSA-DES-CBC3-SHA SSLv3 Kx=DH Au=RSA Enc=3DES(168) Mac=SHA1
58:DES-CBC3-SHA SSLv3 Kx=RSA Au=RSA Enc=3DES(168) Mac=SHA1
So the above setting makes a rather sensible default exclusion
list, while we're still plagued with coddling Exchange 2003 servers.
--
Viktor.
