PKINIT freshness tokensΒΆ
RFC 8070 specifies a pa-data type PA_AS_FRESHNESS, which clients should reflect within signed PKINIT data to prove recent access to the client certificate private key. The contents of a freshness token are left to the KDC implementation. The MIT krb5 KDC uses the following format for freshness tokens (starting in release 1.17):
a four-byte big-endian POSIX timestamp
a four-byte big-endian key version number
an RFC 3961 checksum, with no ASN.1 wrapper
The checksum is computed using the first key in the local krbtgt
principal entry for the realm (e.g. krbtgt/KRBTEST.COM@KRBTEST.COM
if the request is to the KRBTEST.COM realm) of the indicated key
version. The checksum type must be the mandatory checksum type for
the encryption type of the krbtgt key. The key usage value for the
checksum is 514.