//
// Hash58.cs
// 2007-09-16
//
// Unfucking your iPod (in 2 days)
//
// Thanks to everyone on #gtkpod that made this possible (wtbw, nopcode, 
// retar_d, oleavr, desrt and everyone that provided DBs and IDs).
//

using System;
using System.Security.Cryptography;

namespace IPod
{
    public static class Hash58
    {    
        private const int SizeOfHeaders = 0x6C;
    
        public static byte [] GenerateHash(string fwid, byte [] iTunesDB)
        {
            return GenerateHash(fwid, iTunesDB, SizeOfHeaders);
        }
        
        public static byte [] GenerateHash(string fwid, byte [] iTunesDB, int sizeOfHeaders)
        {
            if(fwid == null || fwid.Length != 16) {
                throw new Exception("String FWID must be 16 characters long");
            }
            
            byte [] _fwid = new byte[8];
            for(int i = 0, j = 0; i < fwid.Length; i += 2, j++) {
                _fwid[j] = Convert.ToByte(fwid.Substring(i, 2), 16);
            }

            return GenerateHash(_fwid, iTunesDB, sizeOfHeaders);
        }
    
        public static byte [] GenerateHash(byte [] fwid, byte [] iTunesDB)
        {
            return GenerateHash(fwid, iTunesDB, SizeOfHeaders);
        }
    
        public static byte [] GenerateHash(byte [] fwid, byte [] iTunesDB, int sizeOfHeaders)
        {
            byte [] key = new byte[64];
            byte [] hash = null;
            
            GenerateKey(fwid, key);

            for(int i = 0; i < 64; i++) {
                key[i] ^= 0x36;
            }

            SHA1 sha1 = SHA1.Create();
            sha1.TransformBlock(key, 0, 64, null, 0);
            sha1.TransformFinalBlock(iTunesDB, 0, iTunesDB.Length);
            hash = sha1.Hash;

            for(int i = 0; i < 64; i++) {
                key[i] ^= 0x36 ^ 0x5c;
            }

            sha1 = SHA1.Create();
            sha1.TransformBlock(key, 0, 64, null, 0);
            sha1.TransformFinalBlock(hash, 0, 20);
            return sha1.Hash;
        }

        private static void GenerateKey(byte [] fwid, byte [] key)
        {
            if(fwid.Length != 8) {
                throw new Exception("FWID must be 8 bytes long");
            }

            byte [] y = new byte[16];

            // Take the LCM of each two bytes in the FWID in turn
            for(int i = 0; i < 4; i++) {
                int lcm = Lcm(fwid[i * 2], fwid[i * 2 + 1]);
                byte hi = (byte)((lcm & 0xFF00) >> 8);
                byte lo = (byte)(lcm & 0xFF);

                y[i * 4]     = table1[hi];
                y[i * 4 + 1] = table2[hi];
                y[i * 4 + 2] = table1[lo];
                y[i * 4 + 3] = table2[lo];
            }

            SHA1 sha1 = SHA1.Create();
            sha1.TransformBlock(_fixed, 0, 18, null, 0);
            sha1.TransformFinalBlock(y, 0, 16);
            Array.Copy(sha1.Hash, 0, key, 0, sha1.Hash.Length);
        }

        private static int Gcd(int a, int b)
        {
            while(true) {
                a = a % b;
                if(a == 0) {
                    return b;
                }

                b = b % a;
                if(b == 0) {
                    return a;
                }
            }
        }

        private static int Lcm(int a, int b)
        {
            return a == 0 || b == 0 ? 1 : (a * b) / Gcd(a, b);
        }

        private static byte [] table1 = new byte[256] {
            0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 
            0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
            0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 
            0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
            0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 
            0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
            0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 
            0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
            0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 
            0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
            0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 
            0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
            0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 
            0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
            0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 
            0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
            0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 
            0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
            0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 
            0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
            0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 
            0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
            0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 
            0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
            0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 
            0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
            0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 
            0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
            0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 
            0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
            0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 
            0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16
        };

        private static byte [] table2 = new byte[256] {
            0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 
            0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB,
            0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 
            0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB,
            0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 
            0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E,
            0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 
            0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25,
            0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 
            0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92,
            0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 
            0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84,
            0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 
            0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06,
            0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 
            0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B,
            0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 
            0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73,
            0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 
            0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E,
            0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 
            0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B,
            0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 
            0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4,
            0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 
            0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F,
            0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 
            0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF,
            0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 
            0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61,
            0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 
            0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D
        };

        private static byte [] _fixed = new byte[18] {
            0x67, 0x23, 0xFE, 0x30, 0x45, 0x33, 0xF8, 0x90, 0x99, 0x21, 0x07, 0xC1, 0xD0, 0x12, 0xB2, 0xA1, 0x07, 0x81
        };
    }
}

