[38735] in Kerberos
Re: Password Encryption
daemon@ATHENA.MIT.EDU (Greg Hudson)
Fri May 22 15:43:35 2020
To: Joshua Brodie <josbrodie@gmail.com>, <kerberos@mit.edu>
From: Greg Hudson <ghudson@mit.edu>
Message-ID: <0ff03c01-2ef5-3001-0419-359d4a0c4fab@mit.edu>
Date: Fri, 22 May 2020 15:40:41 -0400
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On 5/22/20 2:29 PM, Joshua Brodie wrote:
> How can I find out the out of the box default password encryption used?
Kerberos doesn't encrypt passwords(*), but it does store long-term keys
derived from the passwords. This derivation, called the "string-to-key"
operation for the encryption type, is one-way; you can't decrypt a
long-term key to get at the original password. You can perform a
dictionary attack (trying lots of potential passwords to see if they
result in the same key). The string-to-key operations for AES and
Camellia enctypes are deliberately slow in order to frustrate dictionary
attacks, whereas the older single-DES, triple-DES, and RC4 enctypes have
very fast string-to-key operations.
The default set of encryption types used for new principals is listed as
the default value of supported_enctypes here:
https://web.mit.edu/kerberos/krb5-latest/doc/admin/conf_files/kdc_conf.html#realms
> On a getprinc -- there are 8 shown -- are these all used for the principal?
Yes, for that principal entry there are string-to-key results for all
eight encryption types. camellia256-cts-cmac and camellia128-cts-cmac
have never been in the default value for supported_enctypes, so the
default was not used for that principal.
(*) Kerberos password-change operations do involve encrypting passwords
for transport over the wire from the client to the admin server. But
the KDC doesn't store decryptable passwords in the database.
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