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cipher suite -adding and removing

Hi, The below statement are really confusing . Does it mean even listing will remove the cipher suite from the machine ?

For example, to remove a cipher from the cipher list, even if it is explicitly stated later in the cipher string, use the following syntax:

tmm --clientciphers 'DEFAULT:!RSA'

For example, to remove the cipher from the cipher list, but add it back to the cipher list if later options allow, use the following syntax:

tmm --clientciphers DEFAULT:-RSA

https://support.f5.com/csp/article/K15194

Thanks

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USER ACCEPTED ANSWER & F5 ACCEPTED ANSWER

Greetings,
I hope this makes sense, here goes:

If you use this syntax, all of the ciphers using RSA KEYX will be removed from the cipher list.

tmm --clientciphers 'DEFAULT:!RSA'

Let say, you'd like to include this cipher for some reason, but only this one:

DES-CBC3-SHA

If you used the ! filter, you would be unable to add that cipher only back:

tmm --clientciphers 'DEFAULT:!RSA:DES-CBC3-SHA' | grep ' DES-CBC3-SHA'
#

So using the - filter, allows you to add only that cipher back, but keep the others filtered out:

tmm --clientciphers 'DEFAULT:-RSA:DES-CBC3-SHA' | grep ' DES-CBC3-SHA'
48:    10  DES-CBC3-SHA                     168  TLS1    Native  DES       SHA     RSA
49:    10  DES-CBC3-SHA                     168  TLS1.1  Native  DES       SHA     RSA
50:    10  DES-CBC3-SHA                     168  TLS1.2  Native  DES       SHA     RSA
51:    10  DES-CBC3-SHA                     168  DTLS1   Native  DES       SHA     RSA
52:    10  DES-CBC3-SHA                     168  SSL3    Native  DES       SHA     RSA

Hope this is helpful!
Kevin

1
Comments on this Answer
Comment made 4 days ago by bluestar007 58

Hi, Thanks for the reply .

You said "If you used the ! filter, you would be unable to add that cipher only back:"

Here is where I am confused . What you mean by unable to add that cipher only back.

What I understood from other threads , If I use "tmm --clientciphers 'DEFAULT:!RSA'" ,It just print the DEFAULT list and filter RSA ,It does not remove it from the BOX .That means we can add it later

Thanks

0
Comment made 4 days ago by Kevin.K

Greetings,

You are correct, it doesn't remove the cipher from the BIG-IP system. Typically, when building filters in this manner, the admin is attempting to build a cipher string for use in the client or server SSL profile. So you could have multiple different virtual servers that reference different SSL profiles, allowing a different set of ciphers for clients to negotiate.

See 'Ciphers' in this article for more detail:

https://support.f5.com/csp/article/K14783

Hope this is helpful!

Kevin

1
Comment made 4 days ago by bluestar007 58
Hi,

ltm profile client-ssl test {
app-service none
cert digicert.crt
cert-key-chain {
    digicert {
        cert digicert.crt
        chain gdigicertchain.crt
        key digicert.key
    }
}
chain gdigicertchain.crt
defaults-from clientssl
inherit-certkeychain false
key digicert.key
passphrase none

}

  1. If I have client profile like above ,which is inheriting from the cientssl profile (client ssl profile uses ciphers DEFAULT")

Now I decided to alter the DEFAULT for profile 'test',Just to remove 'DES-CBC3-SHA' ,the below profile will work ?

ltm profile client-ssl test {
app-service none
cert digicert.crt
cert-key-chain {
    digicert {
        cert digicert.crt
        chain gdigicertchain.crt
        key digicert.key
    }
}
chain gdigicertchain.crt
**ciphers 'DEFAULT:!RSA:DES-CBC3-SHA'** 

defaults-from clientssl
inherit-certkeychain false
key digicert.key
passphrase none

}

2.Let's say I used ' ciphers 'DEFAULT:!RSA' and later on decided to bring all RSA back , reverting the string from 'DEFAULT:!RSA' to 'ciphers 'DEFAULT' will help

Thanks

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Comment made 4 days ago by Kevin.K

Greetings,
1) To just remove DES-CBC3-SHA, you would use: DEFAULT:!DES-CBC3-SHA
2) That is correct.

Hope this is helpful!
Kevin

1
Comment made 3 days ago by bluestar007 58

Hi,

what is the difference between

tmm --clientciphers 'DEFAULT'

openssl --clientciphers 'DEFAULT'

Do we need to play with openssl if we are interested only control plane traffic

Thanks

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Comment made 3 days ago by Kevin.K

Greetings,
TMM's DEFAULT cipher list represent a smaller subset of F5's NATIVE cipher list. NATIVE refers to ciphers that can be hardware accelerated.

OpenSSL would be used by the Configuration utility, Config synchronization and iControl REST which do exist within the control plane. To view the openssl cipher list, use:

openssl ciphers -v

Hope this is helpful!
Kevin

1
Comment made 3 days ago by bluestar007 58

Hi, It means we don't use ciphersuite from openssl in tmm .Only native cipher list can be used for a client profile ?

Thanks

0
Comment made 3 days ago by Kevin.K

Just to be completely thorough, this is true after version 12.0.0. There was a COMPAT stack coded in TMM prior to 12.0.0 that contained some OpenSSL ciphers.

https://support.f5.com/csp/article/K17373

Kevin

1