Public key format

[BasileiosKal]

When using the public key as input to Sign, Verify etc., we can define it either as a point of G2 or as an octet string. Rn we do the later, consistent with what the BLS spec does.

That said, passing it as a G2 point, will simplify the encode for has operation a bit, since we don't need a "special clause" there so we would not append it with it length, since it would be handled like any other point. See also here for context.

IMO defining it as an octet string is more intuitive, but Im fine with both.

[tmarkovski]

Would it make sense to do the same for the secret key (instead "non negative integer mod r") and treat is as scalar, the same way the messages are?

[tplooker]

I'm in favour of keeping this as octet string based input.

[BasileiosKal]

Discussed on WG call on 20th of Mar. Related to #246 and #223. Closing in favor of those issues