/// <summary>
/// 提供用于计算指定文件哈希值的方法
/// <example>例如计算文件的MD5值:
/// <code>
/// String hashMd5=HashHelper.ComputeMD5("MyFile.txt");
/// </code>
/// </example>
/// <example>例如计算文件的CRC32值:
/// <code>
/// String hashCrc32 = HashHelper.ComputeCRC32("MyFile.txt");
/// </code>
/// </example>
/// <example>例如计算文件的SHA1值:
/// <code>
/// String hashSha1 =HashHelper.ComputeSHA1("MyFile.txt");
/// </code>
/// </example>
/// </summary>
public sealed class HashHelper
{
/// <summary>
/// 计算指定文件的MD5值
/// </summary>
/// <param name="fileName">指定文件的完全限定名称</param>
/// <returns>返回值的字符串形式</returns>
public static String ComputeMD5(String fileName)
{
String hashMD5 = String.Empty;
//检查文件是否存在，如果文件存在则进行计算，否则返回空值
if (System.IO.File.Exists(fileName))
{
using (System.IO.FileStream fs = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read))
{
//计算文件的MD5值
System.Security.Cryptography.MD5 calculator=System.Security.Cryptography.MD5.Create();
Byte[] buffer = calculator.ComputeHash(fs);
calculator.Clear();
//将字节数组转换成十六进制的字符串形式
StringBuilder stringBuilder = new StringBuilder();
for (int i = ; i < buffer.Length; i++)
{
stringBuilder.Append(buffer[i].ToString("x2"));
}
hashMD5= stringBuilder.ToString();
}//关闭文件流
}//结束计算
return hashMD5;
}//ComputeMD5
/// <summary>
/// 计算指定文件的CRC32值
/// </summary>
/// <param name="fileName">指定文件的完全限定名称</param>
/// <returns>返回值的字符串形式</returns>
public static String ComputeCRC32(String fileName)
{
String hashCRC32 = String.Empty;
//检查文件是否存在，如果文件存在则进行计算，否则返回空值
if (System.IO.File.Exists(fileName))
{
using (System.IO.FileStream fs = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read))
{
//计算文件的CSC32值
Crc32 calculator = new Crc32();
Byte[] buffer = calculator.ComputeHash(fs);
calculator.Clear();
//将字节数组转换成十六进制的字符串形式
StringBuilder stringBuilder = new StringBuilder();
for (int i = ; i < buffer.Length; i++)
{
stringBuilder.Append(buffer[i].ToString("x2"));
}
hashCRC32 = stringBuilder.ToString();
}//关闭文件流
}
return hashCRC32;
}//ComputeCRC32
/// <summary>
/// 计算指定文件的SHA1值
/// </summary>
/// <param name="fileName">指定文件的完全限定名称</param>
/// <returns>返回值的字符串形式</returns>
public static String ComputeSHA1(String fileName)
{
String hashSHA1 = String.Empty;
//检查文件是否存在，如果文件存在则进行计算，否则返回空值
if (System.IO.File.Exists(fileName))
{
using (System.IO.FileStream fs = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read))
{
//计算文件的SHA1值
System.Security.Cryptography.SHA1 calculator = System.Security.Cryptography.SHA1.Create();
Byte[] buffer = calculator.ComputeHash(fs);
calculator.Clear();
//将字节数组转换成十六进制的字符串形式
StringBuilder stringBuilder = new StringBuilder();
for (int i = ; i < buffer.Length; i++)
{
stringBuilder.Append(buffer[i].ToString("x2"));
}
hashSHA1 = stringBuilder.ToString();
}//关闭文件流
}
return hashSHA1;
}//ComputeSHA1
}//end class: HashHelper
/// <summary>
/// 提供 CRC32 算法的实现
/// </summary>
public class Crc32 : System.Security.Cryptography.HashAlgorithm
{
public const UInt32 DefaultPolynomial = 0xedb88320;
public const UInt32 DefaultSeed = 0xffffffff;
private UInt32 hash;
private UInt32 seed;
private UInt32[] table;
private static UInt32[] defaultTable;
public Crc32()
{
table = InitializeTable(DefaultPolynomial);
seed = DefaultSeed;
Initialize();
}
public Crc32(UInt32 polynomial, UInt32 seed)
{
table = InitializeTable(polynomial);
this.seed = seed;
Initialize();
}
public override void Initialize()
{
hash = seed;
}
protected override void HashCore(byte[] buffer, int start, int length)
{
hash = CalculateHash(table, hash, buffer, start, length);
}
protected override byte[] HashFinal()
{
byte[] hashBuffer = UInt32ToBigEndianBytes(~hash);
this.HashValue = hashBuffer;
return hashBuffer;
}
public static UInt32 Compute(byte[] buffer)
{
return ~CalculateHash(InitializeTable(DefaultPolynomial), DefaultSeed, buffer, , buffer.Length);
}
public static UInt32 Compute(UInt32 seed, byte[] buffer)
{
return ~CalculateHash(InitializeTable(DefaultPolynomial), seed, buffer, , buffer.Length);
}
public static UInt32 Compute(UInt32 polynomial, UInt32 seed, byte[] buffer)
{
return ~CalculateHash(InitializeTable(polynomial), seed, buffer, , buffer.Length);
}
private static UInt32[] InitializeTable(UInt32 polynomial)
{
if (polynomial == DefaultPolynomial && defaultTable != null)
{
return defaultTable;
}
UInt32[] createTable = new UInt32[];
for (int i = ; i < ; i++)
{
UInt32 entry = (UInt32)i;
for (int j = ; j < ; j++)
{
if ((entry & ) == )
entry = (entry >> ) ^ polynomial;
else
entry = entry >> ;
}
createTable[i] = entry;
}
if (polynomial == DefaultPolynomial)
{
defaultTable = createTable;
}
return createTable;
}
private static UInt32 CalculateHash(UInt32[] table, UInt32 seed, byte[] buffer, int start, int size)
{
UInt32 crc = seed;
for (int i = start; i < size; i++)
{
unchecked
{
crc = (crc >> ) ^ table[buffer[i] ^ crc & 0xff];
}
}
return crc;
}
private byte[] UInt32ToBigEndianBytes(UInt32 x)
{
return new byte[] { (byte)((x >> ) & 0xff), (byte)((x >> ) & 0xff), (byte)((x >> ) & 0xff), (byte)(x & 0xff) };
}
}//end class: Crc32