MD5算法原理及C#和JS实现的方法是什么

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一、简介

MD5 是哈希算法（散列算法）的一种应用。Hash 算法虽然被称为算法，但实际上它更像是一种思想。Hash 算法没有一个固定的公式，只要符合散列思想的算法都可以被称为是 Hash 算法。

算法目的就是，把任意长度的输入（又叫做预映射 pre-image），通过散列算法变换成固定长度的输出，该输出就是散列值。

注意，不同的输入可能会散列成相同的输出，所以不能从散列值来确定唯一的输入值。

散列函数简单的说就是：一种将任意长度的消息压缩到某一固定长度的消息摘要的函数。

Hash 算法是一个广义的算法，也可以认为是一种思想，使用 Hash 算法可以提高存储空间的利用率，可以提高数据的查询效率，因为很难找到其逆向规律，也可以做数字签名来保障数据传递的安全性。所以Hash算法被广泛地应用在互联网应用中。

散列值不同 => 原始值不同

如果两个散列值是不相同的（根据同一函数），那么这两个散列值的原始输入也是不相同的。这个特性是散列函数具有确定性的结果。

散列值相同 ≠> 原始值相同

散列函数的输入和输出不是一一对应的，如果两个散列值相同，两个输入值很可能是相同的，但不绝对肯定二者一定相等（可能出现哈希碰撞）。

关于“撞库”（Credential Stuffing Attack）

其在网络安全中是一个古老的概念，按中文的字面意思解读，就是“碰撞数据库”的意思。“碰撞”意味着碰运气，即不一定能成功；而“数据库”中往往存储着大量敏感数据，比如我们登录一个网站所需要的用户名、密码，再比如手机号、身份证号等个人隐私信息。“撞库”在英文中的表述为 Credential Stuffing（密码嗅探），也非常直白的说明了撞库的主要场景：试图获取正确的账号/密码组合，大白话就是“盗号”。

二、C# 代码实现

根据传入参数，返回分大小写的 16 位或 32 位密文，并且可自定义编码规则。

// 测试
string jiamihou16 = SecurityMD5.MD5Encrypt("TestString", 16, false); // 8828701f97fa4511
string jiamihou32 = SecurityMD5.MD5Encrypt("TestString", 32);// 5B56F40F8828701F97FA4511DDCD25FB
/// <summary>
/// MD5 加密方法
/// </summary>
/// <param name="md5instr">待加密字符串</param>
/// <param name="digit">位数：16/32/64</param>
/// <param name="isupper">输出大小写：true 大写；false 小写(返回为 64 位时不区分大小写)</param>
/// <param name="encoding">字符编码规则，为空默认：UTF8</param>
/// <returns></returns>
public static string MD5Encrypt(string md5instr, int digit, bool isupper = true, Encoding encoding = null)
{
    string md5outstr = string.Empty;
    if (encoding == null)
        encoding = Encoding.UTF8;
    switch (digit)
    {
        case 16:
            // SecurityMD5.MD5Encrypt(md5instr, 16, true); // 16位大写
            // SecurityMD5.MD5Encrypt(md5instr, 16, false); // 16位小写
            var md5provider = new MD5CryptoServiceProvider();
            var hashinstr16 = md5provider.ComputeHash(encoding.GetBytes(md5instr));
            md5outstr = BitConverter.ToString(hashinstr16, 4, 8);
            md5outstr = md5outstr.Replace("-", "");
            if (!isupper)
                md5outstr = md5outstr.ToLower();
            return md5outstr;
        case 32:
            // SecurityMD5.MD5Encrypt(md5instr, 32, true); // 32位大写
            // SecurityMD5.MD5Encrypt(md5instr, 32, false); // 32位小写
            MD5 md532 = MD5.Create();
            byte[] hashinstr32 = md532.ComputeHash(encoding.GetBytes(md5instr));
            string upperorlowerflag = isupper ? "X2" : "x2";
            for (int i = 0; i < hashinstr32.Length; i++)
            {
                md5outstr = md5outstr + hashinstr32[i].ToString(upperorlowerflag);
            }
            return md5outstr;
        case 64:
            // SecurityMD5.MD5Encrypt(md5instr, 64); // 64位加密，加密后为24位的值，例如：9GnLVZEzFmZLMj963TqUEQ==
            MD5 md564 = MD5.Create();
            byte[] hashinstr64 = md564.ComputeHash(encoding.GetBytes(md5instr));
            return Convert.ToBase64String(hashinstr64);
        default:
            return "";
    }
}

三、js 代码实现

根据传入参数，返回分大小写的 16 位或 32 位密文。

// 测试
    md5_function("TestString",16,false)
    >'8828701f97fa4511'
    md5_function("TestString",32,true)
    >'5B56F40F8828701F97FA4511DDCD25FB'
// MD5 加密（入参分别是：待加密内容、返回位数、是否为大写）
function md5_function(md5instr, digit, isupper){
    function md5_RotateLeft(lValue, iShiftBits) {
        return (lValue << iShiftBits) | (lValue >>> (32 - iShiftBits));
    }
    function md5_AddUnsigned(lX, lY) {
        var lX4, lY4, lX8, lY8, lResult;
        lX8 = (lX & 0x80000000);
        lY8 = (lY & 0x80000000);
        lX4 = (lX & 0x40000000);
        lY4 = (lY & 0x40000000);
        lResult = (lX & 0x3FFFFFFF) + (lY & 0x3FFFFFFF);
        if (lX4 & lY4) {
            return (lResult ^ 0x80000000 ^ lX8 ^ lY8);
        }
        if (lX4 | lY4) {
            if (lResult & 0x40000000) {
                return (lResult ^ 0xC0000000 ^ lX8 ^ lY8);
            } else {
                return (lResult ^ 0x40000000 ^ lX8 ^ lY8);
            }
        } else {
            return (lResult ^ lX8 ^ lY8);
        }
    }
    function md5_F(x, y, z) {
        return (x & y) | ((~x) & z);
    }
    function md5_G(x, y, z) {
        return (x & z) | (y & (~z));
    }
    function md5_H(x, y, z) {
        return (x ^ y ^ z);
    }
    function md5_I(x, y, z) {
        return (y ^ (x | (~z)));
    }
    function md5_FF(a, b, c, d, x, s, ac) {
        a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_F(b, c, d), x), ac));
        return md5_AddUnsigned(md5_RotateLeft(a, s), b);
    };
    function md5_GG(a, b, c, d, x, s, ac) {
        a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_G(b, c, d), x), ac));
        return md5_AddUnsigned(md5_RotateLeft(a, s), b);
    };
    function md5_HH(a, b, c, d, x, s, ac) {
        a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_H(b, c, d), x), ac));
        return md5_AddUnsigned(md5_RotateLeft(a, s), b);
    };
    function md5_II(a, b, c, d, x, s, ac) {
        a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_I(b, c, d), x), ac));
        return md5_AddUnsigned(md5_RotateLeft(a, s), b);
    };
    function md5_ConvertToWordArray(md5instr) {
        var lWordCount;
        var lMessageLength = md5instr.length;
        var lNumberOfWords_temp1 = lMessageLength + 8;
        var lNumberOfWords_temp2 = (lNumberOfWords_temp1 - (lNumberOfWords_temp1 % 64)) / 64;
        var lNumberOfWords = (lNumberOfWords_temp2 + 1) * 16;
        var lWordArray = Array(lNumberOfWords - 1);
        var lBytePosition = 0;
        var lByteCount = 0;
        while (lByteCount < lMessageLength) {
            lWordCount = (lByteCount - (lByteCount % 4)) / 4;
            lBytePosition = (lByteCount % 4) * 8;
            lWordArray[lWordCount] = (lWordArray[lWordCount] | (md5instr.charCodeAt(lByteCount) << lBytePosition));
            lByteCount++;
        }
        lWordCount = (lByteCount - (lByteCount % 4)) / 4;
        lBytePosition = (lByteCount % 4) * 8;
        lWordArray[lWordCount] = lWordArray[lWordCount] | (0x80 << lBytePosition);
        lWordArray[lNumberOfWords - 2] = lMessageLength << 3;
        lWordArray[lNumberOfWords - 1] = lMessageLength >>> 29;
        return lWordArray;
    };
    function md5_WordToHex(lValue) {
        var WordToHexValue = "", WordToHexValue_temp = "", lByte, lCount;
        for (lCount = 0; lCount <= 3; lCount++) {
            lByte = (lValue >>> (lCount * 8)) & 255;
            WordToHexValue_temp = "0" + lByte.toString(16);
            WordToHexValue = WordToHexValue + WordToHexValue_temp.substr(WordToHexValue_temp.length - 2, 2);
        }
        return WordToHexValue;
    };
    function md5_Utf8Encode(md5instr) {
        md5instr = md5instr?.replace(/
/g, "
");
        var utftext = "";
        for (var n = 0; n < md5instr.length; n++) {
            var c = md5instr.charCodeAt(n);
            if (c < 128) {
                utftext += String.fromCharCode(c);
            } else if ((c > 127) && (c < 2048)) {
                utftext += String.fromCharCode((c >> 6) | 192);
                utftext += String.fromCharCode((c & 63) | 128);
            } else {
                utftext += String.fromCharCode((c >> 12) | 224);
                utftext += String.fromCharCode(((c >> 6) & 63) | 128);
                utftext += String.fromCharCode((c & 63) | 128);
            }
        }
        return utftext;
    };
    var x = Array();
    var k, AA, BB, CC, DD, a, b, c, d;
    var S11 = 7, S12 = 12, S13 = 17, S14 = 22;
    var S21 = 5, S22 = 9, S23 = 14, S24 = 20;
    var S31 = 4, S32 = 11, S33 = 16, S34 = 23;
    var S41 = 6, S42 = 10, S43 = 15, S44 = 21;
    md5instr = md5_Utf8Encode(md5instr);
    x = md5_ConvertToWordArray(md5instr);
    a = 0x67452301; b = 0xEFCDAB89; c = 0x98BADCFE; d = 0x10325476;
    for (k = 0; k < x.length; k += 16) {
        AA = a; BB = b; CC = c; DD = d;
        a = md5_FF(a, b, c, d, x[k + 0], S11, 0xD76AA478);
        d = md5_FF(d, a, b, c, x[k + 1], S12, 0xE8C7B756);
        c = md5_FF(c, d, a, b, x[k + 2], S13, 0x242070DB);
        b = md5_FF(b, c, d, a, x[k + 3], S14, 0xC1BDCEEE);
        a = md5_FF(a, b, c, d, x[k + 4], S11, 0xF57C0FAF);
        d = md5_FF(d, a, b, c, x[k + 5], S12, 0x4787C62A);
        c = md5_FF(c, d, a, b, x[k + 6], S13, 0xA8304613);
        b = md5_FF(b, c, d, a, x[k + 7], S14, 0xFD469501);
        a = md5_FF(a, b, c, d, x[k + 8], S11, 0x698098D8);
        d = md5_FF(d, a, b, c, x[k + 9], S12, 0x8B44F7AF);
        c = md5_FF(c, d, a, b, x[k + 10], S13, 0xFFFF5BB1);
        b = md5_FF(b, c, d, a, x[k + 11], S14, 0x895CD7BE);
        a = md5_FF(a, b, c, d, x[k + 12], S11, 0x6B901122);
        d = md5_FF(d, a, b, c, x[k + 13], S12, 0xFD987193);
        c = md5_FF(c, d, a, b, x[k + 14], S13, 0xA679438E);
        b = md5_FF(b, c, d, a, x[k + 15], S14, 0x49B40821);
        a = md5_GG(a, b, c, d, x[k + 1], S21, 0xF61E2562);
        d = md5_GG(d, a, b, c, x[k + 6], S22, 0xC040B340);
        c = md5_GG(c, d, a, b, x[k + 11], S23, 0x265E5A51);
        b = md5_GG(b, c, d, a, x[k + 0], S24, 0xE9B6C7AA);
        a = md5_GG(a, b, c, d, x[k + 5], S21, 0xD62F105D);
        d = md5_GG(d, a, b, c, x[k + 10], S22, 0x2441453);
        c = md5_GG(c, d, a, b, x[k + 15], S23, 0xD8A1E681);
        b = md5_GG(b, c, d, a, x[k + 4], S24, 0xE7D3FBC8);
        a = md5_GG(a, b, c, d, x[k + 9], S21, 0x21E1CDE6);
        d = md5_GG(d, a, b, c, x[k + 14], S22, 0xC33707D6);
        c = md5_GG(c, d, a, b, x[k + 3], S23, 0xF4D50D87);
        b = md5_GG(b, c, d, a, x[k + 8], S24, 0x455A14ED);
        a = md5_GG(a, b, c, d, x[k + 13], S21, 0xA9E3E905);
        d = md5_GG(d, a, b, c, x[k + 2], S22, 0xFCEFA3F8);
        c = md5_GG(c, d, a, b, x[k + 7], S23, 0x676F02D9);
        b = md5_GG(b, c, d, a, x[k + 12], S24, 0x8D2A4C8A);
        a = md5_HH(a, b, c, d, x[k + 5], S31, 0xFFFA3942);
        d = md5_HH(d, a, b, c, x[k + 8], S32, 0x8771F681);
        c = md5_HH(c, d, a, b, x[k + 11], S33, 0x6D9D6122);
        b = md5_HH(b, c, d, a, x[k + 14], S34, 0xFDE5380C);
        a = md5_HH(a, b, c, d, x[k + 1], S31, 0xA4BEEA44);
        d = md5_HH(d, a, b, c, x[k + 4], S32, 0x4BDECFA9);
        c = md5_HH(c, d, a, b, x[k + 7], S33, 0xF6BB4B60);
        b = md5_HH(b, c, d, a, x[k + 10], S34, 0xBEBFBC70);
        a = md5_HH(a, b, c, d, x[k + 13], S31, 0x289B7EC6);
        d = md5_HH(d, a, b, c, x[k + 0], S32, 0xEAA127FA);
        c = md5_HH(c, d, a, b, x[k + 3], S33, 0xD4EF3085);
        b = md5_HH(b, c, d, a, x[k + 6], S34, 0x4881D05);
        a = md5_HH(a, b, c, d, x[k + 9], S31, 0xD9D4D039);
        d = md5_HH(d, a, b, c, x[k + 12], S32, 0xE6DB99E5);
        c = md5_HH(c, d, a, b, x[k + 15], S33, 0x1FA27CF8);
        b = md5_HH(b, c, d, a, x[k + 2], S34, 0xC4AC5665);
        a = md5_II(a, b, c, d, x[k + 0], S41, 0xF4292244);
        d = md5_II(d, a, b, c, x[k + 7], S42, 0x432AFF97);
        c = md5_II(c, d, a, b, x[k + 14], S43, 0xAB9423A7);
        b = md5_II(b, c, d, a, x[k + 5], S44, 0xFC93A039);
        a = md5_II(a, b, c, d, x[k + 12], S41, 0x655B59C3);
        d = md5_II(d, a, b, c, x[k + 3], S42, 0x8F0CCC92);
        c = md5_II(c, d, a, b, x[k + 10], S43, 0xFFEFF47D);
        b = md5_II(b, c, d, a, x[k + 1], S44, 0x85845DD1);
        a = md5_II(a, b, c, d, x[k + 8], S41, 0x6FA87E4F);
        d = md5_II(d, a, b, c, x[k + 15], S42, 0xFE2CE6E0);
        c = md5_II(c, d, a, b, x[k + 6], S43, 0xA3014314);
        b = md5_II(b, c, d, a, x[k + 13], S44, 0x4E0811A1);
        a = md5_II(a, b, c, d, x[k + 4], S41, 0xF7537E82);
        d = md5_II(d, a, b, c, x[k + 11], S42, 0xBD3AF235);
        c = md5_II(c, d, a, b, x[k + 2], S43, 0x2AD7D2BB);
        b = md5_II(b, c, d, a, x[k + 9], S44, 0xEB86D391);
        a = md5_AddUnsigned(a, AA);
        b = md5_AddUnsigned(b, BB);
        c = md5_AddUnsigned(c, CC);
        d = md5_AddUnsigned(d, DD);
    }
    if(digit == 16){
        if(isupper)
            return (md5_WordToHex(b) + md5_WordToHex(c)).toUpperCase();
        else
            return (md5_WordToHex(b) + md5_WordToHex(c)).toLowerCase();
    }
    else if (digit == 32){
        if(isupper)
            return (md5_WordToHex(a) + md5_WordToHex(b) + md5_WordToHex(c) + md5_WordToHex(d)).toUpperCase();
        else
            return (md5_WordToHex(a) + md5_WordToHex(b) + md5_WordToHex(c) + md5_WordToHex(d)).toLowerCase();
    }
    return "";
}

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