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.
Added information about the required minimum bit length of the public
key. Removed the threshold information as we are not sure now if it's
valid. We'll investigate it separately and make sure a proper validation
for threshold is made.
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.
`4` and `120*time.Seconds` were just some magic numbers in the code.
We decided to move them to separate value declarations to make the
code more self-explanatory.
Piotr Dyraga