获取一个文件的MD5可以先打开一个FileSteam，然后把这个文件流传给一个System.Security.Cryptography.MD5CryptoServiceProvider对象的ComputeHash()方法，这样就可以得到一个文件的MD5。但如何才能得到文件中一部分数据的MD5呢？比如一个100MB的文件，我算前50MB的MD5。以下方法我已考虑过了：
1.把文件中的一部分读取到Byte[]中，但大文件会耗很大的资源，不可行。
2.用文件流的SetLength()方法截取流，但会破坏原文件，而且需要Write权限打开，不可行。
1.把文件中的一部分读取到Byte[]中，但大文件会耗很大的资源，不可行。
2.用文件流的SetLength()方法截取流，但会破坏原文件，而且需要Write权限打开，不可行。
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;using System.Security.Cryptography;namespace MyEncryptFilesProgram
{
public partial class MD5Demo : Form
{
public MD5Demo()
{
InitializeComponent();
} private void button1_Click(object sender, EventArgs e)
{
MD5CryptoServiceProvider MD5 = new MD5CryptoServiceProvider();
this.textBox2.Text = Convert.ToBase64String(MD5.ComputeHash(UnicodeEncoding.Unicode.GetBytes(this.textBox1.Text.Trim())));
}
}
}类using System;
using System.Security.Cryptography;
using System.Text;/// <summary>
/// 非对称加密算法
/// </summary>
namespace AsymmetricCryptography
{
/// <summary>
/// MD5加密类
/// </summary>
public sealed class MD5Encrypt
{
public MD5Encrypt()
{ } /// <summary>
/// 将目标字符串转化为MD5加密值
/// </summary>
/// <param name="source">目标字符串</param>
/// <returns>返回MD5加密值</returns>
public static string GetMd5HashString(string source)
{
//格式化目标字符串
byte[] sourcebytes = ASCIIEncoding.ASCII.GetBytes(source);
byte[] MD5bytes = null;
//声明MD5加密类对象
MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
//生成MD5加密数组
MD5bytes = md5.ComputeHash(sourcebytes);
string strMd5 = "";
//遍历数组中的元素，若位数不足则按照十六进制进行补位
for (int i = 0; i < MD5bytes.Length; i++)
{
if (MD5bytes[i] <= 15)
{
strMd5 += ("0" + MD5bytes[i].ToString("X"));
}
else
{
strMd5 += MD5bytes[i].ToString("X");
}
}
//释放内存中保存的对象
sourcebytes = null;
MD5bytes = null;
md5.Clear();
return strMd5; }
}}
1.产生临时文件会临时占用C盘大量空间，如果用户C盘空间不够，则失败。
2.复制这个大文件的一部分过去会耗费许多时间。我还想到过一个比较另类的方法，传输文件的时候从文件尾开始传起，这样在FileStream可以设置Position算文件的后半部分的MD5，不过这样对文件的检测又比较耗时间和麻烦了。如果能像设置Position一样设置流的结束位置，而又不需要写权限不破坏原文件，那么这个问题就可以完美解决了。
http://www.ietf.org/rfc/rfc1321.txt
public static string MDStream(Stream stream, long begin, long length)[code=C#]using System;
using System.IO;namespace MD5
{
class Class1
{
//static state variables
private static UInt32 A;
private static UInt32 B;
private static UInt32 C;
private static UInt32 D; #region number of bits to rotate in tranforming
private const int S11 = 7;
private const int S12 = 12;
private const int S13 = 17;
private const int S14 = 22;
private const int S21 = 5;
private const int S22 = 9;
private const int S23 = 14;
private const int S24 = 20;
private const int S31 = 4;
private const int S32 = 11;
private const int S33 = 16;
private const int S34 = 23;
private const int S41 = 6;
private const int S42 = 10;
private const int S43 = 15;
private const int S44 = 21;
#endregion #region F, G, H and I are basic MD5 functions
/* F, G, H and I are basic MD5 functions.
* 四个非线性函数:
*
* F(X,Y,Z) =(X&Y)|((~X)&Z)
* G(X,Y,Z) =(X&Z)|(Y&(~Z))
* H(X,Y,Z) =X^Y^Z
* I(X,Y,Z)=Y^(X|(~Z))
*
* （&与，|或，~非，^异或）
*/
private static UInt32 F(UInt32 x, UInt32 y, UInt32 z)
{
return (x & y) | ((~x) & z);
}
private static UInt32 G(UInt32 x, UInt32 y, UInt32 z)
{
return (x & z) | (y & (~z));
}
private static UInt32 H(UInt32 x, UInt32 y, UInt32 z)
{
return x ^ y ^ z;
}
private static UInt32 I(UInt32 x, UInt32 y, UInt32 z)
{
return y ^ (x | (~z));
}
#endregion #region FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4
/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4.
* Rotation is separate from addition to prevent recomputation.
*/
private static void FF(ref UInt32 a, UInt32 b, UInt32 c, UInt32 d, UInt32 mj, int s, UInt32 ti)
{
a = a + F(b, c, d) + mj + ti;
a = a << s | a >> (32 - s);
a += b; // 转换为 ：a=b+((a+F(b,c,d)+mj+ti)<<s) }
private static void GG(ref UInt32 a, UInt32 b, UInt32 c, UInt32 d, UInt32 mj, int s, UInt32 ti)
{
a = a + G(b, c, d) + mj + ti;
a = a << s | a >> (32 - s);
a += b;
}
private static void HH(ref UInt32 a, UInt32 b, UInt32 c, UInt32 d, UInt32 mj, int s, UInt32 ti)
{
a = a + H(b, c, d) + mj + ti;
a = a << s | a >> (32 - s);
a += b;
}
private static void II(ref UInt32 a, UInt32 b, UInt32 c, UInt32 d, UInt32 mj, int s, UInt32 ti)
{
a = a + I(b, c, d) + mj + ti;
a = a << s | a >> (32 - s);
a += b;
}
#endregion private static void MD5_Init()
{
A = 0x67452301; //in memory, this is 0x01234567
B = 0xefcdab89; //in memory, this is 0x89abcdef
C = 0x98badcfe; //in memory, this is 0xfedcba98
D = 0x10325476; //in memory, this is 0x76543210
}
private static void MD5_TrasformBlock(byte[] block)
{ UInt32 a, b, c, d;
UInt32[] x = new UInt32[16];
for(int i = 0, j = 0;i < 64;i += 4, j++)
x[j] = (UInt32)(block[i] | block[i + 1] << 8 | block[i + 2] << 16 | block[i + 3] << 24);
for(int k = 0;k < x.Length;k += 16)
{
a = A;
b = B;
c = C;
d = D; /* Round 1 */
FF(ref a, b, c, d, x[k + 0], S11, 0xd76aa478); /* 1 */
FF(ref d, a, b, c, x[k + 1], S12, 0xe8c7b756); /* 2 */
FF(ref c, d, a, b, x[k + 2], S13, 0x242070db); /* 3 */
FF(ref b, c, d, a, x[k + 3], S14, 0xc1bdceee); /* 4 */
FF(ref a, b, c, d, x[k + 4], S11, 0xf57c0faf); /* 5 */
FF(ref d, a, b, c, x[k + 5], S12, 0x4787c62a); /* 6 */
FF(ref c, d, a, b, x[k + 6], S13, 0xa8304613); /* 7 */
FF(ref b, c, d, a, x[k + 7], S14, 0xfd469501); /* 8 */
FF(ref a, b, c, d, x[k + 8], S11, 0x698098d8); /* 9 */
FF(ref d, a, b, c, x[k + 9], S12, 0x8b44f7af); /* 10 */
FF(ref c, d, a, b, x[k + 10], S13, 0xffff5bb1); /* 11 */
FF(ref b, c, d, a, x[k + 11], S14, 0x895cd7be); /* 12 */
FF(ref a, b, c, d, x[k + 12], S11, 0x6b901122); /* 13 */
FF(ref d, a, b, c, x[k + 13], S12, 0xfd987193); /* 14 */
FF(ref c, d, a, b, x[k + 14], S13, 0xa679438e); /* 15 */
FF(ref b, c, d, a, x[k + 15], S14, 0x49b40821); /* 16 */ /* Round 2 */
GG(ref a, b, c, d, x[k + 1], S21, 0xf61e2562); /* 17 */
GG(ref d, a, b, c, x[k + 6], S22, 0xc040b340); /* 18 */
GG(ref c, d, a, b, x[k + 11], S23, 0x265e5a51); /* 19 */
GG(ref b, c, d, a, x[k + 0], S24, 0xe9b6c7aa); /* 20 */
GG(ref a, b, c, d, x[k + 5], S21, 0xd62f105d); /* 21 */
GG(ref d, a, b, c, x[k + 10], S22, 0x2441453); /* 22 */
GG(ref c, d, a, b, x[k + 15], S23, 0xd8a1e681); /* 23 */
GG(ref b, c, d, a, x[k + 4], S24, 0xe7d3fbc8); /* 24 */
GG(ref a, b, c, d, x[k + 9], S21, 0x21e1cde6); /* 25 */
GG(ref d, a, b, c, x[k + 14], S22, 0xc33707d6); /* 26 */
GG(ref c, d, a, b, x[k + 3], S23, 0xf4d50d87); /* 27 */
GG(ref b, c, d, a, x[k + 8], S24, 0x455a14ed); /* 28 */
GG(ref a, b, c, d, x[k + 13], S21, 0xa9e3e905); /* 29 */
GG(ref d, a, b, c, x[k + 2], S22, 0xfcefa3f8); /* 30 */
GG(ref c, d, a, b, x[k + 7], S23, 0x676f02d9); /* 31 */
GG(ref b, c, d, a, x[k + 12], S24, 0x8d2a4c8a); /* 32 */ /* Round 3 */
HH(ref a, b, c, d, x[k + 5], S31, 0xfffa3942); /* 33 */
HH(ref d, a, b, c, x[k + 8], S32, 0x8771f681); /* 34 */
HH(ref c, d, a, b, x[k + 11], S33, 0x6d9d6122); /* 35 */
HH(ref b, c, d, a, x[k + 14], S34, 0xfde5380c); /* 36 */
HH(ref a, b, c, d, x[k + 1], S31, 0xa4beea44); /* 37 */
HH(ref d, a, b, c, x[k + 4], S32, 0x4bdecfa9); /* 38 */
HH(ref c, d, a, b, x[k + 7], S33, 0xf6bb4b60); /* 39 */
HH(ref b, c, d, a, x[k + 10], S34, 0xbebfbc70); /* 40 */
HH(ref a, b, c, d, x[k + 13], S31, 0x289b7ec6); /* 41 */
HH(ref d, a, b, c, x[k + 0], S32, 0xeaa127fa); /* 42 */
HH(ref c, d, a, b, x[k + 3], S33, 0xd4ef3085); /* 43 */
HH(ref b, c, d, a, x[k + 6], S34, 0x4881d05); /* 44 */
HH(ref a, b, c, d, x[k + 9], S31, 0xd9d4d039); /* 45 */
HH(ref d, a, b, c, x[k + 12], S32, 0xe6db99e5); /* 46 */
HH(ref c, d, a, b, x[k + 15], S33, 0x1fa27cf8); /* 47 */
HH(ref b, c, d, a, x[k + 2], S34, 0xc4ac5665); /* 48 */
II(ref a, b, c, d, x[k + 0], S41, 0xf4292244); /* 49 */
II(ref d, a, b, c, x[k + 7], S42, 0x432aff97); /* 50 */
II(ref c, d, a, b, x[k + 14], S43, 0xab9423a7); /* 51 */
II(ref b, c, d, a, x[k + 5], S44, 0xfc93a039); /* 52 */
II(ref a, b, c, d, x[k + 12], S41, 0x655b59c3); /* 53 */
II(ref d, a, b, c, x[k + 3], S42, 0x8f0ccc92); /* 54 */
II(ref c, d, a, b, x[k + 10], S43, 0xffeff47d); /* 55 */
II(ref b, c, d, a, x[k + 1], S44, 0x85845dd1); /* 56 */
II(ref a, b, c, d, x[k + 8], S41, 0x6fa87e4f); /* 57 */
II(ref d, a, b, c, x[k + 15], S42, 0xfe2ce6e0); /* 58 */
II(ref c, d, a, b, x[k + 6], S43, 0xa3014314); /* 59 */
II(ref b, c, d, a, x[k + 13], S44, 0x4e0811a1); /* 60 */
II(ref a, b, c, d, x[k + 4], S41, 0xf7537e82); /* 61 */
II(ref d, a, b, c, x[k + 11], S42, 0xbd3af235); /* 62 */
II(ref c, d, a, b, x[k + 2], S43, 0x2ad7d2bb); /* 63 */
II(ref b, c, d, a, x[k + 9], S44, 0xeb86d391); /* 64 */ A += a;
B += b;
C += c;
D += d;
}
}
/// <summary>
/// 得到stream的md5
/// </summary>
/// <param name="stream">要处理的流</param>
/// <param name="begin">开始处理的位置</param>
/// <param name="length">要处理的长度</param>
/// <returns></returns>
public static string MDStream(Stream stream, long begin, long length)
{
if(stream == null)
throw new ArgumentNullException();
byte[] block = new byte[64];
UInt64 size = 0;
int b = 0;
MD5_Init();
while(begin-- > 0 && stream.ReadByte() >= 0)
;
if(begin >= 0)
throw new ArgumentException("", "begin");
while((b = stream.ReadByte()) != -1 && length-- > 0)
{
block[size++ % 64] = (byte)b;
if(size % 64 == 0)
MD5_TrasformBlock(block);
}
if(length > 0)
throw new ArgumentException("", "length");
UInt64 bp = size % 64;//blockPoint
block[bp++] = 0x80;
if(bp > 56)
{
while(bp < 64)
block[bp++] = 0;
MD5_TrasformBlock(block);
for(int i = 0;i < 56;i++)
block[i] = 0;
}
else
while(bp < 56)
block[bp++] = 0; size *= 8;
block[56] = (byte)(size & 0xFF);
block[57] = (byte)((size >> 8) & 0xFF);
block[58] = (byte)((size >> 16) & 0xFF);
block[59] = (byte)((size >> 24) & 0xFF);
block[60] = (byte)((size >> 32) & 0xFF);
block[61] = (byte)((size >> 40) & 0xFF);
block[62] = (byte)((size >> 48) & 0xFF);
block[63] = (byte)(size >> 56);
MD5_TrasformBlock(block);
//return new UInt32[] { A, B, C, D };
return string.Format("{0}-{1}-{2}-{3}", BitConverter.ToString(BitConverter.GetBytes(A))
, BitConverter.ToString(BitConverter.GetBytes(B))
, BitConverter.ToString(BitConverter.GetBytes(C))
, BitConverter.ToString(BitConverter.GetBytes(D))).Replace("-", "");
}
}
}
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