Re: CVE-2024-40761: Apache Answer: Avatar URL leaked user email addresses

[Solar Designer <solar () openwall com>]

Hi LinkinStar,

There were several more replies from others, please see in the list
archive if you're not subscribed:

https://www.openwall.com/lists/oss-security/

On Thu, Sep 26, 2024 at 10:10:38AM +0800, LinkinStar wrote:
> Because *Gravatar recommends using sha-256*, we believe there must be a
> reason for its modification. Since the official recommendation is to change
> the encryption method, why not implement it according to the official
> requirements? You must admit that sha-256 is more difficult than md5, even
> if only slightly. Although this may not completely solve the problem, I
> believe following the official recommendation would be marginally better,
> wouldn't it? So I think this fix itself is acceptable.

The change is fine - just don't call it a security fix.  Also, this is
hashing and not encryption.

Others pointed out that Gravatar's recommendation is just that - not a
specification - so unless you need interoperability with other servers
implementing Gravatar, you can do better than SHA-256.  Specifically,
use of a keyed hash such as HMAC-SHA256 was suggested and makes sense to
me - as long as the key is generated from a CSPRNG (such as
/dev/urandom) and is large enough (such as 32 bytes).

Alexander