[Cryptography] Why are Diffie-Hellman key sizes multiples of 64?

[Pierre Abbat]

https://codingtechroom.com/question/understanding-dh-key-size-requirements
As far as I'm aware,
* the operation of the DH protocol depends only on the modulus being prime and 
the generator being relatively prime to it and having large order;
* if the modulus is p, the difficulty of breaking DH may depend on the size of 
the largest factor of p-1 and the size of the largest factor of p+1, depending 
on the attack;
* but there's nothing about the protocol itself that requires the number of 
bits in p to be a multiple of anything.
Does this requirement come from the library they're using? I don't see what's 
wrong with using a 4184-bit or 4235-bit prime, as long as it's a safe prime, 
strong prime, or Fouvry prime.

Pierre
-- 
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