What's up with our MAC support?

[Hal Murray]

>        # 1, the packet is a crypto-NAK; if 3, the packet is
>        # authenticated with DES; if 5, the packet is authenticated

The DES stuff is news to me.

NTP classic had stand alone code for MD5 and SHA1.  We carried that along 
until we decided to require libcrypto.


> I don't know how that relates to the set of MAC lengths implied by
> libcrypto's support list. I didn;t find good search hits for that.

If you pick an algorithm with a digest length bigger than 20 bytes, it gets 
truncated.

I'm not sure what happens if you pick one with a digest length less than 16 
bytes.

attic/digest-find is your friend for things like this.  I should add DES and 
DES3.



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