Just out of curiosity, why?

64 bits message digests are considered unsafe, hardware has become to powerful. 128 bits is only "moderately" safe, if you want your digests to be really secure you have to opt for 512 bits. Or is security not an issue for you?

Update

If you insist on 64 bits message digests I think DES is the way forward, like brother kvale already suggested.

In reply to Re: 64-bit digest algorithms by dHarry
in thread 64-bit digest algorithms by BrowserUk

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