咨询区

• Nick Berardi

请问我如何通过 C# 计算 string 的 crc32 校验和？

回答区

• Pete

我一直震撼的一件事就是 .NET 底层框架中居然没有提供对 CRC32 的直接支持，CRC32 一直都是 ZIP,RAR 压缩中做校验和的绝佳方案，在 .NET 中你可以这么使用。

var crc32 = new Crc32();
var hash = String.Empty;using (var fs = File.Open("c:\\myfile.txt", FileMode.Open))foreach (byte b in crc32.ComputeHash(fs)) hash += b.ToString("x2").ToLower();Console.WriteLine("CRC-32 is {0}", hash);

更详细的资料可参考：https://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net 和 https://github.com/damieng/DamienGKit/blob/master/CSharp/DamienG.Library/Security/Cryptography/Crc32.cs

• SharpC

上面朋友的回答是基于 File 的方式，其实替换成 string 会更加直接，方便，我的项目中定义了一个 Crc32 帮助类，代码如下：

/// <summary>
/// Performs 32-bit reversed cyclic redundancy checks.
/// </summary>
public class Crc32
{#region Constants/// <summary>/// Generator polynomial (modulo 2) for the reversed CRC32 algorithm. /// </summary>private const UInt32 s_generator = 0xEDB88320;#endregion#region Constructors/// <summary>/// Creates a new instance of the Crc32 class./// </summary>public Crc32(){// Constructs the checksum lookup table. Used to optimize the checksum.m_checksumTable = Enumerable.Range(0, 256).Select(i =>{var tableEntry = (uint)i;for (var j = 0; j < 8; ++j){tableEntry = ((tableEntry & 1) != 0)? (s_generator ^ (tableEntry >> 1)) : (tableEntry >> 1);}return tableEntry;}).ToArray();}#endregion#region Methods/// <summary>/// Calculates the checksum of the byte stream./// </summary>/// <param name="byteStream">The byte stream to calculate the checksum for.</param>/// <returns>A 32-bit reversed checksum.</returns>public UInt32 Get<T>(IEnumerable<T> byteStream){try{// Initialize checksumRegister to 0xFFFFFFFF and calculate the checksum.return ~byteStream.Aggregate(0xFFFFFFFF, (checksumRegister, currentByte) => (m_checksumTable[(checksumRegister & 0xFF) ^ Convert.ToByte(currentByte)] ^ (checksumRegister >> 8)));}catch (FormatException e){throw new CrcException("Could not read the stream out as bytes.", e);}catch (InvalidCastException e){throw new CrcException("Could not read the stream out as bytes.", e);}catch (OverflowException e){throw new CrcException("Could not read the stream out as bytes.", e);}}#endregion#region Fields/// <summary>/// Contains a cache of calculated checksum chunks./// </summary>private readonly UInt32[] m_checksumTable;#endregion
}

帮助类定义好后，接下来就可以这么使用了。

var arrayOfBytes = Encoding.ASCII.GetBytes("The quick brown fox jumps over the lazy dog");var crc32 = new Crc32();
Console.WriteLine(crc32.Get(arrayOfBytes).ToString("X"));

对了，你可以用 https://crccalc.com/ 以在线的方式来测试你的 crc32 的输入输出。

点评区

两位大佬提供的方式不错，学习了，最后的 Online ：https://crccalc.com/ 太方便了，有兴趣可以尝试一下。