Md5sum 用于检查说 ubuntu 的 iso 映像的完整性。它是如何工作的？
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算法 Message Digest 5 或 MD5，它是一种单向加密散列函数。MD5 对“消息”（二进制数据，例如 iso 映像）执行许多二进制操作，以计算 128 位“哈希”。
检查下载的包（如 ubuntu）的完整性很有用，因为如果包与经过身份验证的源完全相同，则生成的 MD5 哈希将是相同的。如果下载中有错误（来自网络干扰等），或者如果您下载了一个看起来像 ubuntu 但包含其他代码/其他内容的恶意包，那么 MD5 将不匹配，您会知道有些不同，并且您应该从其他来源重新下载。
更新
如果以上内容对您来说“它是如何工作的”不够字面意思，这里是我自己的 MD5 算法的 javascript 实现：
/**
* JavaScript Class Implementation of RSA Data Security, Inc.
* Message Digest 5 (MD5) Algorithm, as defined in RFC 1321.
*
* @author Dustin C. Fineout <dustin.fineout@gmail.com>
* @created 10/10/2009 11:23:29 AM
* @modified 10/10/2009 12:34:56 PM
* @version 0.1 WORKING
**/
/**
* Usage example:
* var md5 = new MD5();
* alert(md5.hash('Dustin Fineout')); // 8844be37f4e8b3973b48b95b0c69f0b1
**/
function MD5()
{
this.F = function(x,y,z) { return (x & y) | ((~x) & z); };
this.G = function(x,y,z) { return (x & z) | (y & (~z)); };
this.H = function(x,y,z) { return (x ^ y ^ z); };
this.I = function(x,y,z) { return (y ^ (x | (~z))); };
this.C = function(q,a,b,x,s,ac) { return this.addu(this.rol(this.addu(this.addu(a,q),this.addu(x,ac)),s),b); };
this.FF = function(a,b,c,d,x,s,ac) { return this.C((b & c) | ((~b) & d),a,b,x,s,ac); };
this.GG = function(a,b,c,d,x,s,ac) { return this.C((b & d) | (c & (~d)),a,b,x,s,ac); };
this.HH = function(a,b,c,d,x,s,ac) { return this.C(b ^ c ^ d,a,b,x,s,ac); };
this.II = function(a,b,c,d,x,s,ac) { return this.C(c ^ (b | (~d)),a,b,x,s,ac); };
this.hash = function(message)
{
var xl,x=[],k,aa,bb,cc,dd,a=0x67452301,b=0xEFCDAB89,c=0x98BADCFE,d=0x10325476;
x = this.convertToWordArray(this.utf8Encode(message));
xl = x.length;
for (var j = 0; j < xl; j += 16) {
aa=a; bb=b; cc=c; dd=d;
a=this.FF(a,b,c,d,x[j+0],7,0xD76AA478);
d=this.FF(d,a,b,c,x[j+1],12,0xE8C7B756);
c=this.FF(c,d,a,b,x[j+2],17,0x242070DB);
b=this.FF(b,c,d,a,x[j+3],22,0xC1BDCEEE);
a=this.FF(a,b,c,d,x[j+4],7,0xF57C0FAF);
d=this.FF(d,a,b,c,x[j+5],12,0x4787C62A);
c=this.FF(c,d,a,b,x[j+6],17,0xA8304613);
b=this.FF(b,c,d,a,x[j+7],22,0xFD469501);
a=this.FF(a,b,c,d,x[j+8],7,0x698098D8);
d=this.FF(d,a,b,c,x[j+9],12,0x8B44F7AF);
c=this.FF(c,d,a,b,x[j+10],17,0xFFFF5BB1);
b=this.FF(b,c,d,a,x[j+11],22,0x895CD7BE);
a=this.FF(a,b,c,d,x[j+12],7,0x6B901122);
d=this.FF(d,a,b,c,x[j+13],12,0xFD987193);
c=this.FF(c,d,a,b,x[j+14],17,0xA679438E);
b=this.FF(b,c,d,a,x[j+15],22,0x49B40821);
a=this.GG(a,b,c,d,x[j+1],5,0xF61E2562);
d=this.GG(d,a,b,c,x[j+6],9,0xC040B340);
c=this.GG(c,d,a,b,x[j+11],14,0x265E5A51);
b=this.GG(b,c,d,a,x[j+0],20,0xE9B6C7AA);
a=this.GG(a,b,c,d,x[j+5],5,0xD62F105D);
d=this.GG(d,a,b,c,x[j+10],9,0x2441453);
c=this.GG(c,d,a,b,x[j+15],14,0xD8A1E681);
b=this.GG(b,c,d,a,x[j+4],20,0xE7D3FBC8);
a=this.GG(a,b,c,d,x[j+9],5,0x21E1CDE6);
d=this.GG(d,a,b,c,x[j+14],9,0xC33707D6);
c=this.GG(c,d,a,b,x[j+3],14,0xF4D50D87);
b=this.GG(b,c,d,a,x[j+8],20,0x455A14ED);
a=this.GG(a,b,c,d,x[j+13],5,0xA9E3E905);
d=this.GG(d,a,b,c,x[j+2],9,0xFCEFA3F8);
c=this.GG(c,d,a,b,x[j+7],14,0x676F02D9);
b=this.GG(b,c,d,a,x[j+12],20,0x8D2A4C8A);
a=this.HH(a,b,c,d,x[j+5],4,0xFFFA3942);
d=this.HH(d,a,b,c,x[j+8],11,0x8771F681);
c=this.HH(c,d,a,b,x[j+11],16,0x6D9D6122);
b=this.HH(b,c,d,a,x[j+14],23,0xFDE5380C);
a=this.HH(a,b,c,d,x[j+1],4,0xA4BEEA44);
d=this.HH(d,a,b,c,x[j+4],11,0x4BDECFA9);
c=this.HH(c,d,a,b,x[j+7],16,0xF6BB4B60);
b=this.HH(b,c,d,a,x[j+10],23,0xBEBFBC70);
a=this.HH(a,b,c,d,x[j+13],4,0x289B7EC6);
d=this.HH(d,a,b,c,x[j+0],11,0xEAA127FA);
c=this.HH(c,d,a,b,x[j+3],16,0xD4EF3085);
b=this.HH(b,c,d,a,x[j+6],23,0x4881D05);
a=this.HH(a,b,c,d,x[j+9],4,0xD9D4D039);
d=this.HH(d,a,b,c,x[j+12],11,0xE6DB99E5);
c=this.HH(c,d,a,b,x[j+15],16,0x1FA27CF8);
b=this.HH(b,c,d,a,x[j+2],23,0xC4AC5665);
a=this.II(a,b,c,d,x[j+0],6,0xF4292244);
d=this.II(d,a,b,c,x[j+7],10,0x432AFF97);
c=this.II(c,d,a,b,x[j+14],15,0xAB9423A7);
b=this.II(b,c,d,a,x[j+5],21,0xFC93A039);
a=this.II(a,b,c,d,x[j+12],6,0x655B59C3);
d=this.II(d,a,b,c,x[j+3],10,0x8F0CCC92);
c=this.II(c,d,a,b,x[j+10],15,0xFFEFF47D);
b=this.II(b,c,d,a,x[j+1],21,0x85845DD1);
a=this.II(a,b,c,d,x[j+8],6,0x6FA87E4F);
d=this.II(d,a,b,c,x[j+15],10,0xFE2CE6E0);
c=this.II(c,d,a,b,x[j+6],15,0xA3014314);
b=this.II(b,c,d,a,x[j+13],21,0x4E0811A1);
a=this.II(a,b,c,d,x[j+4],6,0xF7537E82);
d=this.II(d,a,b,c,x[j+11],10,0xBD3AF235);
c=this.II(c,d,a,b,x[j+2],15,0x2AD7D2BB);
b=this.II(b,c,d,a,x[j+9],21,0xEB86D391);
a=this.addu(a,aa); b=this.addu(b,bb); c=this.addu(c,cc); d=this.addu(d,dd);
}
return (this.wordToHex(a)+this.wordToHex(b)+this.wordToHex(c)+this.wordToHex(d)).toLowerCase();
};
this.test = function()
{
if (this.hash('Dustin Fineout') == '8844be37f4e8b3973b48b95b0c69f0b1') {
return true;
}
return false;
};
this.addu = function(x, y)
{
var ls = (x & 0xFFFF) + (y & 0xFFFF);
return (((x >> 16) + (y >> 16) + (ls >> 16)) << 16) | (ls & 0xFFFF);
};
this.rol = function(v, s)
{
return (v << s) | (v >>> (32 - s));
};
this.utf8Encode = function(str)
{
return unescape(encodeURIComponent(str));
};
this.convertToWordArray = function(str)
{
var lWordCount;
var lMessageLength = str.length;
var lNumberOfWords_temp1=lMessageLength + 8;
var lNumberOfWords_temp2=(lNumberOfWords_temp1-(lNumberOfWords_temp1 % 64))/64;
var lNumberOfWords = (lNumberOfWords_temp2+1)*16;
var lWordArray=new 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] | (str.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;
};
this.wordToHex = function(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;
};
}
我很乐意根据需要进行注释或扩展 :) 另外，请注意这不是我仍然用于 JavaScript 命名空间的单例模式 - 实际上这是我第一次尝试这种模式 :p 有许多美味的单例模式可用来自道格拉斯·克罗克福德。
于 2009-06-15T17:26:17.643 回答