Create createAggSig, verifyAggSig and verifyWeightedAggSig function

[nazarhussain]

Description

Create three functions createAggSig, verifyAggSig and verifyWeightedAggSig as stated in the LIP in lisk-cryptography

createAggSig(keysList, pubKeySignaturePairs):
    aggregationBits = byte string of length ceil(length(keyList)/8) with all bytes set to 0
    signatures = []
    for pair in pubKeySignaturePairs: 
        signatures.append(pair.sig)
        index = keysList.index(pair.pubkey)
        set bit at position index to 1 in aggregationBits
    signature = Aggregate(signatures)
    return (aggregationBits, signature)

verifyAggSig(keysList, aggregationBits, signature, tag, networkIdentifier, message):
    taggedMessage = convert2BLSSignatureInput(tag, networkIdentifier, message)
    keys = []
    for every i in [0, …, ceil(length(keyList)/8)]:
        if i-th bit of aggregationBits is set to 1:
            keys.append(keysList[i])
    return FastAggregateVerify(keys, taggedMessage, signature)


verifyWeightedAggSig(keysList, aggregationBits, signature, tag, networkIdentifier, weights, threshold, message):
    taggedMessage = convert2BLSSignatureInput(tag, networkIdentifier, message)
    keys = []
    weightSum = 0
    for every i in [0, …, ceil(length(keyList)/8)]:
        if i-th bit of aggregationBits is set to 1:
            keys.append(keysList[i])
            weightSum += weights[i]
    if weightSum < threshold:
        return INVALID
    return FastAggregateVerify(keys, taggedMessage, signature)

Motivation

Generate aggregated compact signatures with with BLS signature scheme.

Acceptance Criteria

• lisk-crytography would have two functions defined above
• These functions must be covered with few test scenarios

Additional Information

• We can use eth-2 test vectors or our own test vector to cover tests for above
• blst-ts wrapper library already contains the implementation of aggregated signatures and verification. So we need to double check if its the same as we have then we can reuse.