Calculating Elf-32 in C# and .NET

November 24th 2007 • .NET (.NET, CSharp, hashing) • 1,252 views • 4 responses

Because you can never have enough hashing algorithms at your disposal this one is compatible with the elf_hash function that forms part of the Executable and Linkable Format.

using System;
using System.Security.Cryptography;

public class Elf32 : HashAlgorithm {
   private UInt32 hash;

   public Elf32() {
      Initialize();
   }

   public override void Initialize() {
      hash = 0;
   }

   protected override void HashCore(byte[] buffer, int start, int length) {
      hash = CalculateHash(hash, buffer, start, length);
   }

   protected override byte[] HashFinal() {
      byte[] hashBuffer = UInt32ToBigEndianBytes(hash);
      this.HashValue = hashBuffer;
      return hashBuffer;
   }

   public override int HashSize { get { return 32; } }

   public static UInt32 Compute(UInt32 polynomial, UInt32 seed, byte[] buffer) {
      return CalculateHash(seed, buffer, 0, buffer.Length);
   }

   private static UInt32 CalculateHash(UInt32 seed, byte[] buffer, int start, int size) {
      UInt32 hash = seed;

      for (int i = start; i < size; i++)
         unchecked {
            hash = (hash << 4) + buffer[i];
            UInt32 work = (hash & 0xf0000000);
            if (work != 0)
               hash ^= (work >> 24);
            hash &= ~work;
         }
      return hash;
   }

   private byte[] UInt32ToBigEndianBytes(UInt32 x) {
      return new byte[] {
         (byte)((x >> 24) & 0xff),
         (byte)((x >> 16) & 0xff),
         (byte)((x >> 8) & 0xff),
         (byte)(x & 0xff)
      };
   }
}

[)amien