使用 python 计算字符串的 HMAC 时出现问题

Question

我正在尝试编写一个程序来计算字符串的 hmac。我可以使用 hashlib 库，但不能使用 hmac。这是我的代码：

from hashlib import sha256

def string_to_decimal(string):
    res = ''
    for char in string:
        res += hex(ord(char))[2:]
    return int(res, 16)

def decimal_to_string(number):
    hex_number = hex(number)[2:]
    hex_number = hex_number[::-1]
    res = ''
    for i in range(0, len(hex_number), 2):
        if i + 1 < len(hex_number):
            res += chr(int(hex_number[i + 1] + hex_number[i], 16))
        else:
            res += chr(int(hex_number[i], 16))

    return res[::-1]

def calculate_ipad_opad(block_size, ipad, opad):
    res_ipad = 0
    res_opad = 0
    for i in range(block_size // 8):
        res_ipad = (res_ipad * 256) + ipad
        res_opad = (res_opad * 256) + opad
    return res_ipad, res_opad

def integer_to_bytes(number):
    res = list()
    while number > 0:
        res.append(number % 256)
        number //= 256
    
    return bytes(res[::-1])

block_size = 512

msg = 'The quick brown fox jumps over the lazy dog'
key = 'key'

ipad = 54
opad = 92

block_ipad, block_opad = calculate_ipad_opad(block_size, ipad, opad)

key_decimal = string_to_decimal(key)
si = key_decimal ^ block_ipad
so = key_decimal ^ block_opad

a = sha256(integer_to_bytes(so) + sha256(integer_to_bytes(si) + msg.encode()).digest())

print(a.digest())

我知道密钥长度不超过块大小。我使用 Wikipedia 编写代码。但它不能正常工作。你能帮我解决一下吗？？？

编辑： 我预计代码的输出为 f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8。但是输出是 3d6243123b984bcc17cb96eb61c2b47d27545c3a9119b623be7932e846bf0643.

Answer 1

键的右侧必须用 0x00 值填充到摘要的块大小（如果键大小小于块大小，这里就是这种情况）。您可以通过例如在 return:

之前添加 string_to_decimal()

res = res.ljust(64 * 2, "0")

通过此更改，提供了预期的结果。

对于实现，最好使用更详细的算法规范，例如FIPS PUB 198-1 instead of the highly abbreviated description in Wikipedia. Furthermore, you are on the safe side if official test vectors 已应用。

实际上不需要转换为十进制数，即可以像对象一样直接使用字节，这大大简化了实现：

from hashlib import sha256

msg = 'The quick brown fox jumps over the lazy dog'
key = 'key'

block_size_bytes = 64

block_opad_bytes = b'\x5c' * block_size_bytes
block_ipad_bytes = b'\x36' * block_size_bytes
key_bytes = key.encode().ljust(block_size_bytes, b'[=11=]')

si_bytes = bytes([a ^ b for (a, b) in zip(block_ipad_bytes, key_bytes)]) 
so_bytes = bytes([a ^ b for (a, b) in zip(block_opad_bytes, key_bytes)]) 

a = sha256(so_bytes + sha256(si_bytes + msg.encode()).digest())

print(a.digest().hex()) # f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8

使用 python 计算字符串的 HMAC 时出现问题

Problem with calculating HMAC of a string with python

python

cryptography

sha256

hmac

message-authentication-code