from typing import List

def mask_r(r: int) -> int:
    r_bytes = r.to_bytes(16, "little")

    r_masked = bytearray(r_bytes)
    r_masked[3] &= 15;
    r_masked[7] &= 15;
    r_masked[11] &= 15;
    r_masked[15] &= 15;
    r_masked[4] &= 252;
    r_masked[8] &= 252;
    r_masked[12] &= 252;


    r_masked = int.from_bytes(r_masked, "little")

    return r_masked


def poly1305(message: bytes, r: int, s: int):
    r = mask_r(r)
    p = 2**130-5
    acc = 0

    blocks = [int.from_bytes(message[i:i+16], "little") for i in range(0, len(message), 16)]

    for block in blocks:
        byte_length = (block.bit_length() + 7) // 8
        
        block += 1 << (8*byte_length)

        acc = ((acc+block)*r) % p

    acc += s

    return acc & (2**128-1)

    
def main():
    r = 0xa806d542fe52447f336d555778bed685
    s = 0x1bf54941aff6bf4afdb20dfb8a800301
    
    golden_result = 0xa927010caf8b2bc2c6365130c11d06a8

    msg = b"Cryptographic Forum Research Group"

    result = poly1305(msg, r, s)

    print(f"{golden_result:x}")
    print(f"{result:x}")

if __name__ == "__main__":
    main()