For an odd n-bit number, we can't find two n-1-bit numbers which
multiplied gives an n-bit number. That's why public key length n must be
an even number.
I have also renamed AreSafePrimes to IsSafePrime since only the first
function argument is considered to be a safe prime according to a safe
prime definition.
Instead of passing safe prime bit length which is a kind of an
implementation detail, we should pass a public key bit length. Public
key is a Paillier modulus defining plaintext space. This information is
more important than the safe prime value/bit length used under the hood.
First of all, we should check both `p,p1` and `q,q1` in the `TestInitPsAndQs`. Moreover, it's better to operate on primes in `TestArePsAndQsGood` and in `TestInitShortcuts` because non-prime numbers are not allowed there in a real world and tests were a bit misleading because of it.
Piotr Dyraga