#C# - 393 bytes [cracked](http://codegolf.stackexchange.com/a/51277/11180)

    using System;class P{static void Main(string[]a){int l=a[0].Length;l=l%8==0?l/8:l/8+1;var b=new byte[l][];for(int i=0;i<l;i++){b[i]=new byte[8];};int j=l-1,k=7;for(int i=0;i<a[0].Length;i++){b[j][k]=Convert.ToByte(""+a[0][i],16);k--;if((i+1)%8==0){j--;k=7;}}var c=0xcbf29ce484222325;for(int i=0;i<l;i++){for(int o=0;o<8;o++){c^=b[i][o];c*=0x100000001b3;}}Console.WriteLine(c.ToString("X"));}}

Ungolfed:

    using System;
    class P
    {
        static void Main(string[]a)
        {
          int l = a[0].Length;
          l = l % 8 == 0 ? l / 8 : l / 8 + 1;
          var b = new byte[l][];
          for (int i = 0; i < l; i++) { b[i] = new byte[8]; };
          int j = l-1, k = 7;
          for (int i = 0; i < a[0].Length; i++)
          {
            b[j][k] = Convert.ToByte(""+a[0][i], 16);
            k--;
            if((i+1) % 8 == 0)
            {
              j--;
              k = 7;
            }
          }
          var c = 0xcbf29ce484222325;
          for (int i = 0; i < l; i++)
          {
            for (int o = 0; o < 8; o++)
            {
              c ^= b[i][o];
              c *= 0x100000001b3;
            }
          }
          Console.WriteLine(c.ToString("X"));
        }
    }


I have never touched cryptography or hashing in my life, so be gentle :)

It's a simple implementation of an [FNV-1a](http://www.isthe.com/chongo/tech/comp/fnv/index.html) hash with some array pivoting on the input. I am sure there is a better way of doing this but this is the best I could do.

It might use a bit of memory on long inputs.