python - 隐写术 - UnicodeDecodeError

Question

我正在编写一个 Python 脚本来隐藏图像中的数据。它基本上隐藏了.PNG中每个像素的RGB映射中红色的最后两位中的位。该脚本适用于小写字母，但会产生带有句号的错误。它会产生这个错误：

Traceback（最近一次调用最后一次）：文件 “E:\Python\Steganography\main.py”，第 65 行，在 print(unhide('coded-img.png')) 文件“E:\Python\Steganography\main.py”，第 60 行，取消隐藏 message = bin2str(binary) 文件“E:\Python\Steganography\main.py”，第 16 行，在 bin2str 中 return n.to_bytes((n.bit_length() + 7) // 8, 'big').decode() UnicodeDecodeError: 'utf-8' codec can't decode byte 0x80 in position 6：无效的起始字节

这是我的代码：

from PIL import Image

def str2bin(message):
    binary = bin(int.from_bytes(message.encode('utf-8'), 'big'))
    return binary[2:]

def bin2str(binary):
    n = int(binary, 2)
    return n.to_bytes((n.bit_length() + 7) // 8, 'big').decode()

def hide(filename, message):
    image = Image.open(filename)
    binary = str2bin(message) + '00000000'

    data = list(image.getdata())

    newData = []

    index = 0
    for pixel in data:
        if index < len(binary):
            pixel = list(pixel)
            pixel[0] >>= 2
            pixel[0] <<= 2
            pixel[0] += int('0b' + binary[index:index+2], 2)
            pixel = tuple(pixel)
            index += 2

        newData.append(pixel)

    print(binary)

    image.putdata(newData)
    image.save('coded-'+filename, 'PNG')

def unhide(filename):
    image = Image.open(filename)
    data = image.getdata()

    binary = '0'

    index = 0

    while binary[-8:] != '00000000':
        binary += bin(data[index][0])[-2:]
        index += 1

    binary = binary[:-1]

    print(binary)
    print(index*2)

    message = bin2str(binary)
    return message


hide('img.png', 'alpha.')
print(unhide('coded-img.png'))

请帮忙。谢谢！

Answer 1

您的代码至少有两个问题。

第一个问题是您的编码可能会错位 1 位，因为 bin() 函数的输出中不包含前导空位：

>>> bin(int.from_bytes('a'.encode('utf-8'), 'big'))[2:]
'1100001'
# This string is of odd length and (when joined with the terminating '00000000')
# turns into a still odd-length '110000100000000' which is then handled by your
# code as if there was an extra trailing zero (so that the length is even).
# During decoding you compensate for that effect with the
#
#       binary = binary[:-1]
#
# line. The latter is responsible for your stated problem when the binary
# representation of your string is in fact of even length and doesn't need
# the extra bit as in the below example:
>>> bin(int.from_bytes('.'.encode('utf-8'), 'big'))[2:]
'101110'

您最好通过在前面添加一个额外的空位（如果需要）来补充二进制字符串的长度。

另一个问题是，在恢复隐藏消息时，停止条件 binary[-8:] == '00000000' 可以通过将一个（部分恢复）符号的前导位连接到另一个符号的尾随位来过早地满足。例如，在以下情况下可能会发生这种情况

• 符号 @（ASCII 码=64，即未设置 6 个低位）后跟任何 ASCII 码值小于 64 的字符（即未设置 2 个最高位） );

• 一个空格字符（ASCII 码=32，即 4 个低位未设置）后跟换行符/换行符（ASCII 码=10，即 4 个高位未设置）。

您可以通过要求在最后 8 位似乎全部未设置时解码完整字节来修复该错误：

while not (len(binary) % 8 == 0 and binary[-8:] == '00000000'):
    # ...