# Implementations of GCM with 64-bit cipher

The paper The Galois/Counter Mode of Operation (GCM) describes mainly the 128-bit case, for use with 128-bit block ciphers such as AES. AES-GCM test vectors are available from NIST.

The paper also describes GCM for 64-bit block ciphers. My question is, has anyone actually implemented GCM for a 64-bit block cipher, and/or published test vectors?

This would not be recommended in most cases. Note that AES-GCM fails terribly if an IV repeats. In a 64-bit block cipher, if you want the probability of such a failure to be below $$2^{-32}$$, then you would be very limited in the number of messages you can encrypt. If you can guarantee a unique IV each time, and are not using a random IV in order to get uniqueness, then maybe it can be OK.