Next: , Previous: Incremental propagation, Up: Setting up a realm

4.11 Encryption types and salting

The encryption types that the KDC is going to assign by default is possible to change. Since the keys used for user authentication is salted the encryption types are described together with the salt strings.

Salting is used to make it harder to pre-calculate all possible keys. Using a salt increases the search space to make it almost impossible to pre-calculate all keys. Salting is the process of mixing a public string (the salt) with the password, then sending it through an encryption type specific string-to-key function that will output the fixed size encryption key.

In Kerberos 5 the salt is determined by the encryption type, except in some special cases.

In des there is the Kerberos 4 salt (none at all) or the afs-salt (using the cell (realm in AFS lingo)).

In arcfour (the encryption type that Microsoft Windows 2000 uses) there is no salt. This is to be compatible with NTLM keys in Windows NT 4.

[kadmin]default_keys in krb5.conf controls what salting to use.

The syntax of [kadmin]default_keys is `[etype:]salt-type[:salt-string]'. `etype' is the encryption type (des-cbc-crc, arcfour-hmac-md5, aes256-cts-hmac-sha1-96), salt-type is the type of salt (pw-salt or afs3-salt), and the salt-string is the string that will be used as salt (remember that if the salt is appended/prepended, the empty salt "" is the same thing as no salt at all).

Common types of salting include