问题描述
Md5sum用于检查ubuntu的iso映像的完整性.它是如何工作的?
Md5sum is used to check integrity of iso image of say ubuntu.How does it work?
推荐答案
消息摘要5或MD5算法，它是一种单向加密哈希函数. MD5对消息"(二进制数据，例如iso图像)执行许多二进制运算，以计算128位的哈希".
The algorithm Message Digest 5 or MD5, it is a one-way cryptographic hash function. MD5 performs many binary operations on the "message" (binary data, for example of an iso image) to compute a 128-bit "hash".
检查下载的软件包(如ubuntu)的完整性很有用，因为如果软件包与经过身份验证的源完全相同，则生成MD5哈希将完全相同.如果下载中存在错误(由于网络干扰等)，或者您下载的恶意软件包看起来像ubuntu，但包含其他代码/其他内容，则MD5将不匹配，您会发现有所不同，并且您应该从其他来源再次下载.
It is useful to check the integrity of a downloaded package such as ubuntu because generating the MD5 hash will be identical if the package is exactly the same as the authenticated source. If there are errors in the download (from network interference, etc.) or if you downloaded a malicious package that was made to look like ubuntu but contained other code/whatever, then the MD5 would not match and you would know something was different and you should download again from a different source.
更新
如果上面的方法在字面上不足以为您解释它是如何工作的"，那么这是我自己的MD5算法的javascript实现:
If the above doesn't explain "how it works" quite literally enough for you, here is my own javascript implementation of the MD5 algorithm:
/**
* JavaScript Class Implementation of RSA Data Security, Inc.
* Message Digest 5 (MD5) Algorithm, as defined in RFC 1321.
*
* @author Dustin C. Fineout <[email protected]>
* @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;
};
}
我将很乐意根据需要注释或扩展:)另外，请注意，这不是我仍用于JavaScript名称空间的单例模式-实际上，这是我第一次尝试这种模式:p有很多美味道格拉斯·克罗克福德(Douglas Crockford)可提供单例模式.
I'll be happy to annotate or expand as desired :) Also, please note this isn't the singleton pattern I still use for JavaScript namespaces - it was actually my first attempt at such a pattern :p There are many delicious singleton patterns available from Douglas Crockford.
这篇关于MD5Sum算法如何工作?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！