哈希函数将任意长度的二进制字符串映射为固定长度的小型二进制字符串。加密哈希函数有这样一个属性：在计算不大可能找到散列为相同的值的两个不同的输入；也就是说，两组数据的哈希值仅在对应的数据也匹配时才会匹配。数据的少量更改会在哈希值中产生不可预知的大量更改。
MD5 算法的哈希值大小为 128 位。
MD5 类的 ComputeHash 方法将哈希作为 16 字节的数组返回。请注意，某些 MD5 实现会生成 32 字符的十六进制格式哈希。若要与此类实现进行互操作，请将 ComputeHash 方法的返回值格式化为十六进制值。
示例
下面的代码示例计算字符串的 MD5 哈希值，并将该哈希作为 32 字符的十六进制格式字符串返回。此代码示例中创建的哈希字符串与能创建 32 字符的十六进制格式哈希字符串的任何 MD5 哈希函数（在任何平台上）兼容。
using System;
using System.Security.Cryptography;
using System.Text;
class Example
{
// Hash an input string and return the hash as
// a 32 character hexadecimal string.
static string getMd5Hash(string input)
{
// Create a new instance of the MD5CryptoServiceProvider object.
MD5 md5Hasher = MD5.Create();
// Convert the input string to a byte array and compute the hash.
byte[] data = md5Hasher.ComputeHash(Encoding.Default.GetBytes(input));
// Create a new Stringbuilder to collect the bytes
// and create a string.
StringBuilder sBuilder = new StringBuilder();
// Loop through each byte of the hashed data
// and format each one as a hexadecimal string.
for (int i = 0; i < data.Length; i++)
{
sBuilder.Append(data[i].ToString("x2"));
}
// Return the hexadecimal string.
return sBuilder.ToString();
}
// Verify a hash against a string.
static bool verifyMd5Hash(string input, string hash)
{
// Hash the input.
string hashOfInput = getMd5Hash(input);
// Create a StringComparer an comare the hashes.
StringComparer comparer = StringComparer.OrdinalIgnoreCase;
if (0 == comparer.Compare(hashOfInput, hash))
{
return true;
}
else
{
return false;
}
}
static void Main()
{
string source = "Hello World!";
string hash = getMd5Hash(source);
Console.WriteLine("The MD5 hash of " + source + " is: " + hash + ".");
Console.WriteLine("Verifying the hash...");
if (verifyMd5Hash(source, hash))
{
Console.WriteLine("The hashes are the same.");
}
else
{
Console.WriteLine("The hashes are not same.");
}
}
}
// This code example produces the following output:
//
// The MD5 hash of Hello World! is: ed076287532e86365e841e92bfc50d8c.
// Verifying the hash...
// The hashes are the same.
代码：
1）获取文件MD5字符串：
// filename：文件的物理路径（如：D:dwbexcelAA.xls）
string ByteArrayToHexString(string filename) {
FileStream fs = new FileStream(filename, FileMode.Open);
MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
md5.Initialize();
byte[] bytes = md5.ComputeHash(fs);
md5.Clear();
fs.Close();
StringBuilder sb = new StringBuilder();
foreach (byte b in bytes)
sb.Append(b.ToString("x2"));
return sb.ToString();
}
2）加密配置文件：
string sSecretKey;// 密钥
先生成加密解密需要的密钥 sSecretKey = GenerateKey();
/// <summary>
/// 根据KEY生成密钥
/// </summary>
/// <param name="key">KEY字符串</param>
/// <returns></returns>
string GenerateKey(string key)
{
byte[] keys = new byte[8];
int j = 0;
for (int i = 0; i < keys.Length; i++)
{
keys[i] = Convert.ToByte(System.Text.Encoding.Unicode.GetBytes(key.Substring(j, 1))[0] - 5);
j += 2;
}
byte[] keys1 = new byte[8];
for (int i = 0; i < keys.Length; i++)
{
keys1[i] = keys[keys.Length - i - 1];
}
return ASCIIEncoding.ASCII.GetString(keys1);
}
/// <summary>
/// 加密文件
/// </summary>
/// <param name="sInputFilename">需要加密的文件（包括路径）</param>
/// <param name="sOutputFilename">加密后的文件（包括路径）</param>
/// <param name="sKey">密钥</param>
void EncryptFile(string sInputFilename, string sOutputFilename, string sKey)
{
FileStream fsInput = new FileStream(sInputFilename, FileMode.Open, FileAccess.Read);
FileStream fsEncrypted = new FileStream(sOutputFilename, FileMode.Create, FileAccess.Write);
DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
ICryptoTransform desencrypt = DES.CreateEncryptor();
CryptoStream cryptostream = new CryptoStream(fsEncrypted, desencrypt, CryptoStreamMode.Write);
byte[] bytearrayinput = new byte[fsInput.Length];
fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);
cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);
cryptostream.Close();
fsInput.Close();
fsEncrypted.Close();
}
3）解密配置文件：
/// <summary>
/// 解密文件
/// </summary>
/// <param name="sInputFilename">需要解密的文件（包括路径）</param>
/// <param name="sOutputFilename">解密后的文件（包括路径）</param>
/// <param name="sKey">密钥</param>
void DecryptFile(string sInputFilename, string sOutputFilename, string sKey)
{
DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
//A 64 bit key and IV is required for this provider.
//Set secret key For DES algorithm.
DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
//Set initialization vector.
DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
FileStream fsread = new FileStream(sInputFilename, FileMode.Open, FileAccess.Read);
ICryptoTransform desdecrypt = DES.CreateDecryptor();
CryptoStream cryptostreamDecr = new CryptoStream(fsread, desdecrypt, CryptoStreamMode.Read);
StreamWriter fsDecrypted = new StreamWriter(sOutputFilename);
fsDecrypted.Write(new StreamReader(cryptostreamDecr).ReadToEnd());
fsDecrypted.Flush();
fsDecrypted.Close();
fsread.Close();
}