python - 预处理 SHA256 Python 实现

Question

我正在维基百科上完成 SHA256 的实现，但遇到了困难。我刚刚尝试编写消息预处理的代码，最终消息的长度是 504 位，而不是所需的 512 位。

维基百科:SHA256

Pre-processing:

append the bit '1' to the message

append k bits '0', where k is the minimum number >= 0 such that the resulting message length (modulo 512 in bits) is 448.

append length of message (without the '1' bit or padding), in bits, as 64-bit big-endian integer (this will make the entire post-processed length a multiple of 512 bits)

我不确定缺陷在哪里，我已经检查过代码好几次了。

def joe_sha256 ( input_string ):
    "Joe's SHA256 implementation"

    # Create a binary version of the input string
    binary_string = create_binary ( input_string )

    # Append '1' bit to the end as per the SHA256 specification
    appended_1_bit_string = append_bit_1 ( binary_string )

    # Append 'k' bits to allow for len(string) % 512 == 488
    appended_k_string = append_k_bit ( appended_1_bit_string )

    # Append length of message
    length_of_message = append_length_of_message ( binary_string )

    # Create final message
    final_message = appended_k_string + length_of_message

    print(len(final_message)) # This prints out 504, it should be 512!!!!

    return final_message # Just for testing.


def create_binary ( input_string ):
    "Takes a string and outputs its binary form"
    A = ''.join(format(ord(x), 'b').zfill(8) for x in input_string)
    return A


def append_bit_1 ( input_string ):
    "Appends the bit 1 to the binary form"
    input_string = input_string + '1'
    return input_string


def append_k_bit ( input_string ):
    "Makes sure the length of input will become X % 512 == 488"
    if len(input_string) % 512 == 488:
        return input_string
    else:
        while len(input_string) % 512 != 488:
            input_string = input_string + '0'
        return input_string


def append_length_of_message ( input_string ):
    ""
    # Get value
    hex = format(len(input_string),'x')

    # Construct the 64 bit number?
    final_num = ''
    length = 16-len(hex)
    for x in range(length):
        final_num = final_num + '0'

    final_num = final_num + hex

    return final_num

Answer 1

有两个问题:

1) 代码中的 488 魔数(Magic Number)应该是 448。

2) 您在append_length_of_message() 中只使用了16 个“位”(字符)。

嗨!