帮助我进行XOR加密

Question

我写了这段代码C#用密钥加密字符串:

private static int Bin2Dec(string num)
{
    int _num = 0;

    for (int i = 0; i < num.Length; i++)
        _num += (int)Math.Pow(2, num.Length - i - 1) * int.Parse(num[i].ToString());

    return _num;
}

private static string Dec2Bin(int num)
{
    if (num < 2) return num.ToString();

    return Dec2Bin(num / 2) + (num % 2).ToString();
}

public static string StrXor(string str, string key)
{
    string _str = "";
    string _key = "";
    string _xorStr = "";
    string _temp = "";

    for (int i = 0; i < str.Length; i++)
    {
        _temp = Dec2Bin(str[i]);    

        for (int j = 0; j < 8 - _temp.Length + 1; j++)
            _temp = '0' + _temp;

        _str += _temp;
    }

    for (int i = 0; i < key.Length; i++)
    {
        _temp = Dec2Bin(key[i]);

        for (int j = 0; j < 8 - _temp.Length + 1; j++)
            _temp = '0' + _temp;

        _key += _temp;
    }    

    while (_key.Length < _str.Length) _key += _key;

    if (_key.Length > _str.Length) _key = _key.Substring(0, _str.Length);

    for (int i = 0; i < _str.Length; i++)
        if (_str[i] == _key[i]) { _xorStr += '0'; } else { _xorStr += '1'; }

    _str = "";

    for (int i = 0; i < _xorStr.Length; i += 8)
    {
        char _chr = (char)0;
        _chr = (char)Bin2Dec(_xorStr.Substring(i, 8)); //ERROR : (Index and length must refer to a location within the string. Parameter name: length)
        _str += _chr;
    }

    return _str;
}

问题是,当我想用​​这段代码解密加密文本时,我总是会收到错误:

string enc_text = ENCRYPT.XORENC("abc","a"); // enc_text = " ??"
string dec_text = ENCRYPT.XORENC(enc_text,"a"); // ArgumentOutOfRangeException

有线索吗？

Answer 1

如果你有一个字符a char,你可以把它转换成一个整数,一个int.

然后您可以使用^运算符对其执行XOR.您此刻似乎没有使用该运算符,这可能是您的问题的根源.

string EncryptOrDecrypt(string text, string key)
{
    var result = new StringBuilder();

    for (int c = 0; c < text.Length; c++)
        result.Append((char)((uint)text[c] ^ (uint)key[c % key.Length]));

    return result.ToString();
}

那种事.这是一个带有注释的较长版本,它们在步骤中执行相同的操作,以便更容易学习:

string EncryptOrDecrypt(string text, string key)
{
    var result = new StringBuilder();

    for (int c = 0; c < text.Length; c++)
    {
        // take next character from string
        char character = text[c];

        // cast to a uint
        uint charCode = (uint)character;

        // figure out which character to take from the key
        int keyPosition = c % key.Length; // use modulo to "wrap round"

        // take the key character
        char keyChar = key[keyPosition];

        // cast it to a uint also
        uint keyCode = (uint)keyChar;

        // perform XOR on the two character codes
        uint combinedCode = charCode ^ keyCode;

        // cast back to a char
        char combinedChar = (char)combinedCode;

        // add to the result
        result.Append(combineChar);
    }

    return result.ToString();
}

短版本是相同的但删除了中间变量,直接将表达式替换为它们的使用位置.