Calculate next slot prev_randao

prev_randao.py

import hashlib
import string

##### Helper function #####
ssz_byteorder = "little" # https://github.com/ethereum/consensus-specs/blob/dev/ssz/simple-serialize.md

# https://github.com/ethereum/consensus-specs/blob/dev/ssz/simple-serialize.md#aliases
def isBytesN(input_):
    # BytesN := Vector[uint8, N]
    assert isinstance(input_, list)
    assert all(isinstance(h, bytes) for h in input_)
    assert all((int(h.hex(), 16) < 2**8) for h in input_)
    return True

# https://github.com/ethereum/consensus-specs/blob/dev/ssz/simple-serialize.md#basic-types
def isUintNString(input_, N):
    assert isinstance(input_, str)
    assert all(c in string.hexdigits for c in input_)
    assert len(input_) % (N // 4) == 0
    return True

def hexToBytesN(input_):
    assert isUintNString(input_, 8)
    return [int(f"{a}{b}", 16).to_bytes(8 // 8, ssz_byteorder) for a, b in zip(input_[0::2], input_[1::2])]

def bytesNToHex(input_):
    assert isBytesN(input_)
    input_hex = [h.hex() for h in input_]
    return f"0x{''.join(input_hex)}"

# https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/beacon-chain.md#hash
def hashFunc(input_):
    assert isBytesN(input_)
    h = hashlib.new('sha256')
    for byte in input_:
        h.update(byte)
    return hexToBytesN(h.hexdigest())

# https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/beacon-chain.md#xor
def xor(bytes_1, bytes_2):
    assert all([isBytesN(bytes_1), isBytesN(bytes_2)])
    assert len(bytes_1) == len(bytes_2)
    return [(int.from_bytes(a, ssz_byteorder) ^ int.from_bytes(b, ssz_byteorder)).to_bytes(8 // 8, ssz_byteorder) for a, b in zip(bytes_1, bytes_2)]

##### Main function #####
if __name__ == "__main__":
    # (T-1)th slot := 4810145 (block_number := 15646555)
    # (T)th slot   := 4810146 (block_number := 15646556)
    
    # Some information we've already known
    prev_randao_4810145   = "0xab2dc18a256fd4dc62debeddf2d2d8ef3e9801bde1bf2e4b5cf57680e9de1982"
    randao_reveal_4810145 = "0xa1510a1b094b716fbce31774c59ec33fe5d3d5d1da5f14c70a4db806aa3bddc80bd3bd3977d0f19bd622d0fa722557a4026ffca0c661c650bdc8e3d1d0128308d0cecdb7529b5e735d6763206fad9f19dba099dc3d0fb17941ab35d7b98fcd01"
    prev_randao_4810146   = "0x7494e81527372a7d3305a32703e2e0bcfad7646436ab4521bcc02f1e0cbdd6be"
    
    # [Step 0] Previous slot information
    prev_randao_T_1   = prev_randao_4810145
    randao_reveal_T_1 = randao_reveal_4810145

    # [Step 1] Convert hex string to `bytes`
    prev_randao_T_1_Bytes32   = hexToBytesN(prev_randao_T_1[2:])
    randao_reveal_T_1_Bytes96 = hexToBytesN(randao_reveal_T_1[2:])

    # [Step 2] Calculate SHA256 of `randao_reveal`
    hash_of_randao_reveal_T_1_Bytes32 = hashFunc(randao_reveal_T_1_Bytes96)

    # [Step 3] Calculate XOR of SHA256(`randao_reveal`) and `prev_randao`
    prev_randao_T_Bytes32 = xor(prev_randao_T_1_Bytes32, hash_of_randao_reveal_T_1_Bytes32)

    # [Step 4] Print the result
    assert bytesNToHex(prev_randao_T_Bytes32) == prev_randao_4810146
    print(f"prev_randao: {prev_randao_4810146}")
    print(f"My result:   {bytesNToHex(prev_randao_T_Bytes32)}")

• Useful links
  https://etherscan.io/block/15646555#consensusinfo
  https://etherscan.io/block/15646556#consensusinfo
• Execution payload of the slot 4810145 on consensus layer has block number 15646555.

Revisions 2: re-write codes that follow the Ethereum consensus-specs

Revisions 3: update codes to calculate slot 4810145 and 4810146