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Date: Fri, 27 Nov 2020 13:58:50 +0100
From: magnum <>
Subject: Re: cracking HMAC-SHA1 (key=salt)

On 2020-11-27 11:52, Sebastian Reitenbach wrote:
> prepared hash file for john:
> tryhackme#e5d8870e5bdd26602cab8dbe07a942c8669e56d6
> however, john --format=HMAC-SHA1 doesn't crack it, as it's using the password as key,
> instead of the salt.

Indeed: Since you know the password we can verify the reverse:

$ echo '481616481616#e5d8870e5bdd26602cab8dbe07a942c8669e56d6' >
$ ./john -form:hmac-sha1 -mask:tryhackme
Press 'q' or Ctrl-C to abort, almost any other key for status
tryhackme        (?)
1g 0:00:00:00  100.0g/s 100.0p/s 100.0c/s 100.0C/s tryhackme
No remaining hashes

...but this only works for verifying a known password, of course.

> I was looking through the formats john supports, as well as the DYNAMIC documentation,
> but was unable to spot anything that could help me to crack that hash with john.
> Can I crack HMAC-SHA1 (key=salt) hashes with JtR, am I overlooking something?

Unfortunately not. We have some old issue for implementing HMAC "salt is 
key" but the demand seems low.


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