Amavis - DKIM sign 256 or 1024 bits?

[Scott Kitterman]

On Monday, November 05, 2012 11:09:47 AM gedir.goncalves at bndes.gov.br wrote:
> Hi, good morning.
> 
> I would like to take a doubt with colleagues from the list.
> 
> I installed and I enabled Amavis 2.6.6 in environmet of the test, I
> created DKIM Key 1024 bit and sign is working properly. But I have a
> doubts, when I see the message header I see that the signature is recorded
> 256.
> 
> In the message header
> 
> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=
>         xxxxx.com.br; h=content-transfer-encoding
> 
>         :content-type:content-type:subject:subject:mime-version
>         :user-agent:from:from:date:date:message-id:received:received; s=
> 
>         dkim; t=1351617962; x=1353432362; bh=s3Zo4hefg9P4WNPsdXL+YJX/u3j
>         iqbMu5IIjUP+cxek=; b=UB+mSlbovScaBSBmlW11vO1fhydVjFP3L2B0X5OA9v/
>         tNo2uMnu2ek4Wao9JDFtayhX38Cp/wQNPQbAgt6iwq1Vks+zhG2u/9cSgF3CVPPw
>         vHlWn2MUZzpZ2/t7G+8xm9Pqqmfvpg6E20HFY8be3UaOQyqAE18/HK+FxCyfvc9w
>         =
> 
> ******Note "a=rsa-sha256".
> 
> 
> When I,m generating the key...
> 
> [root at vrt0488 ~]# amavisd genrsa /var/db/dkim/xxxxx-dkim.key.pem
> ==> Private RSA key successfully written to file
> "/var/db/dkim/xxxxx-dkim.key.pem" (1024 bits, PEM format)
> 
> 
> In the Amavisd.conf configuration...
> 
> $enable_dkim_signing = 1;
> dkim_key('xxxxx.com.br', 'dkim', '/var/db/dkim/xxxxx-dkim.key.pem');
> @dkim_signature_options_bysender_maps = (
>       { '.' => { ttl => 21*24*3600, c => 'relaxed/simple' } } );
> 
> 
> My doubts: I'm signed messages with keys of 256 or 1024 bits? If, 256, how
> can I sign with keys 1024?

Sha256 is the name of an encryption algorithm.  It is not the key length.  
Based on the information you provided, you have a 1024 bit key.

Scott K