Re: [Dcrup] Time For People To Really Stop Using SHA-1 Signatures?

[Hector Santos <[e-mail]>]

On 1/10/2020 7:21 PM, Jim Fenton wrote:

> Someone with access to a more comprehensive corpus of email than my home
> domain might want to catalog and try to contact domains using SHA-1, and
> encourage them to change: "some recipients may not trust your DKIM
> signatures any more". Some PR (magazine articles, etc.) might help, too.

I am not too keen with the false reporting and illusion of insecurity 
when it doesn't exist. Its would a lie to say, "Its not secured" and 
in fact, it is.  As stated, DNS has a bigger potential is being a 
major problem for users.  Putting all your faith in a BROWSER or a 
single vendor to "Trust Them" (but you have to pay them first) is a 
bigger risk.

Whether SHA1 usage is 10%, 5% or 1%, we need to remember, it is still 
part of the protocol and DKIM Verifiers MUST be including SHA1 for 
verification purposes.

    https://tools.ietf.org/html/rfc6376#page-13
    3.3.  Signing and Verification Algorithms

    DKIM supports multiple digital signature algorithms.  Two algorithms
    are defined by this specification at this time: rsa-sha1 and rsa-
    sha256.  Signers MUST implement and SHOULD sign using rsa-sha256.
    Verifiers MUST implement both rsa-sha1 and rsa-sha256.

       INFORMATIVE NOTE: Although rsa-sha256 is strongly encouraged, some
       senders might prefer to use rsa-sha1 when balancing security
       strength against performance, complexity, or other needs.  In
       general, however, rsa-sha256 should always be used whenever
       possible.

Not having it (with suggestions or ideas to remove SHA1 from APIs, 
tools) WILL cause immediate problems.

-- 
HLS