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Robert Allerstorfer

2005-Jul-24 09:37 UTC

[Dovecot] ssl_cipher_list

Hi,

I have noticed the 'ssl_cipher_list' directive in the 1.0-test
snapshots which is not in 0.99. It's default value seems to be
"all:!low". However, this would not be compatible with openssl's
cipher listing format. Thus, I would vote to change it's format to be
openssl compatible. To be compatible, it has to be changed to
"ALL:!LOW" (just upercased in this case). IMO, this would be helpful
because executing

openssl ciphers -v 'all:!low'

would not return any cipher, but

openssl ciphers -v 'ALL:!LOW'

would return the expected cipher list such as

ADH-AES256-SHA          SSLv3 Kx=DH       Au=None Enc=AES(256)  Mac=SHA1
DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1
DHE-DSS-AES256-SHA      SSLv3 Kx=DH       Au=DSS  Enc=AES(256)  Mac=SHA1
AES256-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(256)  Mac=SHA1
ADH-AES128-SHA          SSLv3 Kx=DH       Au=None Enc=AES(128)  Mac=SHA1
DHE-RSA-AES128-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-DSS-AES128-SHA      SSLv3 Kx=DH       Au=DSS  Enc=AES(128)  Mac=SHA1
AES128-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-DSS-RC4-SHA         SSLv3 Kx=DH       Au=DSS  Enc=RC4(128)  Mac=SHA1
EXP1024-DHE-DSS-RC4-SHA SSLv3 Kx=DH(1024) Au=DSS  Enc=RC4(56)   Mac=SHA1 export
EXP1024-RC4-SHA         SSLv3 Kx=RSA(1024) Au=RSA  Enc=RC4(56)   Mac=SHA1 export
EXP1024-DHE-DSS-DES-CBC-SHA SSLv3 Kx=DH(1024) Au=DSS  Enc=DES(56)   Mac=SHA1
export
EXP1024-DES-CBC-SHA     SSLv3 Kx=RSA(1024) Au=RSA  Enc=DES(56)   Mac=SHA1 export
EXP1024-RC2-CBC-MD5     SSLv3 Kx=RSA(1024) Au=RSA  Enc=RC2(56)   Mac=MD5  export
EXP1024-RC4-MD5         SSLv3 Kx=RSA(1024) Au=RSA  Enc=RC4(56)   Mac=MD5  export
EXP-KRB5-RC4-MD5        SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(40)   Mac=MD5  export
EXP-KRB5-RC2-CBC-MD5    SSLv3 Kx=KRB5     Au=KRB5 Enc=RC2(40)   Mac=MD5  export
EXP-KRB5-DES-CBC-MD5    SSLv3 Kx=KRB5     Au=KRB5 Enc=DES(40)   Mac=MD5  export
EXP-KRB5-RC4-SHA        SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(40)   Mac=SHA1 export
EXP-KRB5-RC2-CBC-SHA    SSLv3 Kx=KRB5     Au=KRB5 Enc=RC2(40)   Mac=SHA1 export
EXP-KRB5-DES-CBC-SHA    SSLv3 Kx=KRB5     Au=KRB5 Enc=DES(40)   Mac=SHA1 export
KRB5-RC4-MD5            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=MD5 
KRB5-DES-CBC3-MD5       SSLv3 Kx=KRB5     Au=KRB5 Enc=3DES(168) Mac=MD5 
KRB5-RC4-SHA            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=SHA1
KRB5-DES-CBC3-SHA       SSLv3 Kx=KRB5     Au=KRB5 Enc=3DES(168) Mac=SHA1
EDH-RSA-DES-CBC3-SHA    SSLv3 Kx=DH       Au=RSA  Enc=3DES(168) Mac=SHA1
EXP-EDH-RSA-DES-CBC-SHA SSLv3 Kx=DH(512)  Au=RSA  Enc=DES(40)   Mac=SHA1 export
EDH-DSS-DES-CBC3-SHA    SSLv3 Kx=DH       Au=DSS  Enc=3DES(168) Mac=SHA1
EXP-EDH-DSS-DES-CBC-SHA SSLv3 Kx=DH(512)  Au=DSS  Enc=DES(40)   Mac=SHA1 export
DES-CBC3-SHA            SSLv3 Kx=RSA      Au=RSA  Enc=3DES(168) Mac=SHA1
EXP-DES-CBC-SHA         SSLv3 Kx=RSA(512) Au=RSA  Enc=DES(40)   Mac=SHA1 export
EXP-RC2-CBC-MD5         SSLv3 Kx=RSA(512) Au=RSA  Enc=RC2(40)   Mac=MD5  export
RC4-SHA                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=SHA1
RC4-MD5                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=MD5 
EXP-RC4-MD5             SSLv3 Kx=RSA(512) Au=RSA  Enc=RC4(40)   Mac=MD5  export
ADH-DES-CBC3-SHA        SSLv3 Kx=DH       Au=None Enc=3DES(168) Mac=SHA1
EXP-ADH-DES-CBC-SHA     SSLv3 Kx=DH(512)  Au=None Enc=DES(40)   Mac=SHA1 export
ADH-RC4-MD5             SSLv3 Kx=DH       Au=None Enc=RC4(128)  Mac=MD5 
EXP-ADH-RC4-MD5         SSLv3 Kx=DH(512)  Au=None Enc=RC4(40)   Mac=MD5  export
DES-CBC3-MD5            SSLv2 Kx=RSA      Au=RSA  Enc=3DES(168) Mac=MD5 
RC2-CBC-MD5             SSLv2 Kx=RSA      Au=RSA  Enc=RC2(128)  Mac=MD5 
EXP-RC2-CBC-MD5         SSLv2 Kx=RSA(512) Au=RSA  Enc=RC2(40)   Mac=MD5  export
RC4-MD5                 SSLv2 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=MD5 
EXP-RC4-MD5             SSLv2 Kx=RSA(512) Au=RSA  Enc=RC4(40)   Mac=MD5  export

I want dovecot to only accept high encrypted ciphers, thus it should
support

ssl_cipher_list = ALL:!ADH!LOW:!SSLv2:!EXP:+HIGH:+MEDIUM

corresponding to a openssl list such as

DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1
DHE-DSS-AES256-SHA      SSLv3 Kx=DH       Au=DSS  Enc=AES(256)  Mac=SHA1
AES256-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(256)  Mac=SHA1
KRB5-DES-CBC3-MD5       SSLv3 Kx=KRB5     Au=KRB5 Enc=3DES(168) Mac=MD5 
KRB5-DES-CBC3-SHA       SSLv3 Kx=KRB5     Au=KRB5 Enc=3DES(168) Mac=SHA1
EDH-RSA-DES-CBC3-SHA    SSLv3 Kx=DH       Au=RSA  Enc=3DES(168) Mac=SHA1
EDH-DSS-DES-CBC3-SHA    SSLv3 Kx=DH       Au=DSS  Enc=3DES(168) Mac=SHA1
DES-CBC3-SHA            SSLv3 Kx=RSA      Au=RSA  Enc=3DES(168) Mac=SHA1
DHE-RSA-AES128-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-DSS-AES128-SHA      SSLv3 Kx=DH       Au=DSS  Enc=AES(128)  Mac=SHA1
AES128-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-DSS-RC4-SHA         SSLv3 Kx=DH       Au=DSS  Enc=RC4(128)  Mac=SHA1
KRB5-RC4-MD5            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=MD5 
KRB5-RC4-SHA            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=SHA1
RC4-SHA                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=SHA1
RC4-MD5                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=MD5

This would really make "Dovecot (...) written with security primarily
in mind"

Thanks for consideration!
rob.

Timo Sirainen

2005-Jul-24 14:06 UTC

head link

[Dovecot] ssl_cipher_list

On Sun, 2005-07-24 at 11:37 +0200, Robert Allerstorfer
wrote:> I have noticed the 'ssl_cipher_list' directive in the 1.0-test
> snapshots which is not in 0.99. It's default value seems to be
> "all:!low". However, this would not be compatible with
openssl's
> cipher listing format. Thus, I would vote to change it's format to be
> openssl compatible. To be compatible, it has to be changed to
> "ALL:!LOW" (just upercased in this case). IMO, this would be
helpful
> because executing
I noticed the Debian bugreport about this. ALL:!LOW is actually the
default internally, all:!low is shown only in dovecot-example.conf. I've
changed that already.
> I want dovecot to only accept high encrypted ciphers, thus it should
> support
> 
> ssl_cipher_list = ALL:!ADH!LOW:!SSLv2:!EXP:+HIGH:+MEDIUM
But will it break some clients? Especially some mobile phones? Are there
some recommendations of what that list should contain?
> This would really make "Dovecot (...) written with security primarily
> in mind"
Well, it's just the SSL part and only thing it does is to prevent
correctly behaving but lowly-secured clients from connecting. Perhaps
the default should be different depending on if disable_plaintext_auth
setting. At least there's no reason to prevent lowly secured connections
from working if the "fix" is to disable SSL entirely.

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Robert Allerstorfer

2005-Jul-24 17:45 UTC

head link

[Dovecot] ssl_cipher_list

On Sun, 24 Jul 2005, 17:06 GMT+03 Timo Sirainen wrote:
> On Sun, 2005-07-24 at 11:37 +0200, Robert Allerstorfer wrote:
>> I have noticed the 'ssl_cipher_list' directive in the 1.0-test
>> snapshots which is not in 0.99. It's default value seems to be
>> "all:!low". However, this would not be compatible with
openssl's
>> cipher listing format. Thus, I would vote to change it's format to
be
>> openssl compatible. To be compatible, it has to be changed to
>> "ALL:!LOW" (just upercased in this case).
> I noticed the Debian bugreport about this. ALL:!LOW is actually the
> default internally, all:!low is shown only in dovecot-example.conf.
> I've changed that already.
Thank you!
>> I want dovecot to only accept high encrypted ciphers, thus it should
>> support
>> 
>> ssl_cipher_list = ALL:!ADH!LOW:!SSLv2:!EXP:+HIGH:+MEDIUM
> But will it break some clients? Especially some mobile phones? Are
> there
> some recommendations of what that list should contain?
I'm pretty sure it will, but I don't care, as long Mozilla and other
popular MUAs supports the strong ciphers. Apache's mod_ssl
'SSLCipherSuite' Directive has
"ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP" as the default - see
http://httpd.apache.org/docs/2.0/mod/mod_ssl.html#sslciphersuite

The +HIGH:+MEDIUM:+LOW:+SSLv2:+EXP at the end only affects the ranking
of the ciphers and should ensure to have more stronger ciphers on top.

ALL:!LOW and ALL:!LOW:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP result in the
same list, but the latter returns it in a better order, to prefer
"better" ciphers if they are suitable.

best,
rob.

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