// 
// Copyright (c) 2006 Damien Miller <djm@mindrot.org>
// Copyright (c) 2010 Ryan D. Emerle
// 
// Permission to use, copy, modify, and distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

using Renci.SshNet.Abstractions;
using System;
using System.Diagnostics;
using System.Security.Cryptography;
using System.Text;

namespace Renci.SshNet.Security.Cryptography
{
    /// <summary>BCrypt implementation.</summary>
    /// <remarks>
    ///  <para>
    ///        BCrypt implements OpenBSD-style Blowfish password hashing using the scheme described in
    ///        <a href="http://www.usenix.org/event/usenix99/provos/provos_html/index.html">"A Future-
    ///        Adaptable Password Scheme"</a> by Niels Provos and David Mazieres.
    ///  </para>
    ///  <para>
    ///        This password hashing system tries to thwart off-line password cracking using a
    ///        computationally-intensive hashing algorithm, based on Bruce Schneier's Blowfish cipher.
    ///        The work factor of the algorithm is parameterised, so it can be increased as computers
    ///        get faster.
    ///  </para>
    ///  <para>
    ///        Usage is really simple. To hash a password for the first time, call the <see
    ///        cref="HashPassword(string)"/> method with a random salt, like this:
    ///  </para>
    ///  <code>string pw_hash = BCrypt.HashPassword(plain_password);</code>
    ///  <para>
    ///        To check whether a plaintext password matches one that has been hashed previously,
    ///        use the <see cref="Verify"/> method:
    ///  </para>
    ///  <code>
    ///     if (BCrypt.Verify(candidate_password, stored_hash))
    ///         Console.WriteLine("It matches");
    ///     else
    ///         Console.WriteLine("It does not match");
    ///   </code>
    ///   <para>
    ///         The <see cref="GenerateSalt()"/> method takes an optional parameter (workFactor) that
    ///         determines the computational complexity of the hashing:
    ///   </para>
    ///   <code>
    ///     string strong_salt = BCrypt.GenerateSalt(10);
    ///     string stronger_salt = BCrypt.GenerateSalt(12);
    ///   </code>
    ///   <para>
    ///         The amount of work increases exponentially (2^workFactor), so each increment is twice
    ///         as much work. The default workFactor is 10, and the valid range is 4 to 31.
    ///   </para>
    /// </remarks>
    internal sealed class BCrypt
    {
        // BCrypt parameters
        private const int GENSALT_DEFAULT_LOG2_ROUNDS = 10;
        private const int BCRYPT_SALT_LEN = 16;

        // Blowfish parameters
        private const int BLOWFISH_NUM_ROUNDS = 16;

        // Initial contents of key schedule
        private static readonly uint[] _POrig = {
            0x243f6a88, 0x85a308d3, 0x13198a2e, 0x03707344,
            0xa4093822, 0x299f31d0, 0x082efa98, 0xec4e6c89,
            0x452821e6, 0x38d01377, 0xbe5466cf, 0x34e90c6c,
            0xc0ac29b7, 0xc97c50dd, 0x3f84d5b5, 0xb5470917,
            0x9216d5d9, 0x8979fb1b
        };

        private static readonly uint[] _SOrig = {
            0xd1310ba6, 0x98dfb5ac, 0x2ffd72db, 0xd01adfb7,
            0xb8e1afed, 0x6a267e96, 0xba7c9045, 0xf12c7f99,
            0x24a19947, 0xb3916cf7, 0x0801f2e2, 0x858efc16,
            0x636920d8, 0x71574e69, 0xa458fea3, 0xf4933d7e,
            0x0d95748f, 0x728eb658, 0x718bcd58, 0x82154aee,
            0x7b54a41d, 0xc25a59b5, 0x9c30d539, 0x2af26013,
            0xc5d1b023, 0x286085f0, 0xca417918, 0xb8db38ef,
            0x8e79dcb0, 0x603a180e, 0x6c9e0e8b, 0xb01e8a3e,
            0xd71577c1, 0xbd314b27, 0x78af2fda, 0x55605c60,
            0xe65525f3, 0xaa55ab94, 0x57489862, 0x63e81440,
            0x55ca396a, 0x2aab10b6, 0xb4cc5c34, 0x1141e8ce,
            0xa15486af, 0x7c72e993, 0xb3ee1411, 0x636fbc2a,
            0x2ba9c55d, 0x741831f6, 0xce5c3e16, 0x9b87931e,
            0xafd6ba33, 0x6c24cf5c, 0x7a325381, 0x28958677,
            0x3b8f4898, 0x6b4bb9af, 0xc4bfe81b, 0x66282193,
            0x61d809cc, 0xfb21a991, 0x487cac60, 0x5dec8032,
            0xef845d5d, 0xe98575b1, 0xdc262302, 0xeb651b88,
            0x23893e81, 0xd396acc5, 0x0f6d6ff3, 0x83f44239,
            0x2e0b4482, 0xa4842004, 0x69c8f04a, 0x9e1f9b5e,
            0x21c66842, 0xf6e96c9a, 0x670c9c61, 0xabd388f0,
            0x6a51a0d2, 0xd8542f68, 0x960fa728, 0xab5133a3,
            0x6eef0b6c, 0x137a3be4, 0xba3bf050, 0x7efb2a98,
            0xa1f1651d, 0x39af0176, 0x66ca593e, 0x82430e88,
            0x8cee8619, 0x456f9fb4, 0x7d84a5c3, 0x3b8b5ebe,
            0xe06f75d8, 0x85c12073, 0x401a449f, 0x56c16aa6,
            0x4ed3aa62, 0x363f7706, 0x1bfedf72, 0x429b023d,
            0x37d0d724, 0xd00a1248, 0xdb0fead3, 0x49f1c09b,
            0x075372c9, 0x80991b7b, 0x25d479d8, 0xf6e8def7,
            0xe3fe501a, 0xb6794c3b, 0x976ce0bd, 0x04c006ba,
            0xc1a94fb6, 0x409f60c4, 0x5e5c9ec2, 0x196a2463,
            0x68fb6faf, 0x3e6c53b5, 0x1339b2eb, 0x3b52ec6f,
            0x6dfc511f, 0x9b30952c, 0xcc814544, 0xaf5ebd09,
            0xbee3d004, 0xde334afd, 0x660f2807, 0x192e4bb3,
            0xc0cba857, 0x45c8740f, 0xd20b5f39, 0xb9d3fbdb,
            0x5579c0bd, 0x1a60320a, 0xd6a100c6, 0x402c7279,
            0x679f25fe, 0xfb1fa3cc, 0x8ea5e9f8, 0xdb3222f8,
            0x3c7516df, 0xfd616b15, 0x2f501ec8, 0xad0552ab,
            0x323db5fa, 0xfd238760, 0x53317b48, 0x3e00df82,
            0x9e5c57bb, 0xca6f8ca0, 0x1a87562e, 0xdf1769db,
            0xd542a8f6, 0x287effc3, 0xac6732c6, 0x8c4f5573,
            0x695b27b0, 0xbbca58c8, 0xe1ffa35d, 0xb8f011a0,
            0x10fa3d98, 0xfd2183b8, 0x4afcb56c, 0x2dd1d35b,
            0x9a53e479, 0xb6f84565, 0xd28e49bc, 0x4bfb9790,
            0xe1ddf2da, 0xa4cb7e33, 0x62fb1341, 0xcee4c6e8,
            0xef20cada, 0x36774c01, 0xd07e9efe, 0x2bf11fb4,
            0x95dbda4d, 0xae909198, 0xeaad8e71, 0x6b93d5a0,
            0xd08ed1d0, 0xafc725e0, 0x8e3c5b2f, 0x8e7594b7,
            0x8ff6e2fb, 0xf2122b64, 0x8888b812, 0x900df01c,
            0x4fad5ea0, 0x688fc31c, 0xd1cff191, 0xb3a8c1ad,
            0x2f2f2218, 0xbe0e1777, 0xea752dfe, 0x8b021fa1,
            0xe5a0cc0f, 0xb56f74e8, 0x18acf3d6, 0xce89e299,
            0xb4a84fe0, 0xfd13e0b7, 0x7cc43b81, 0xd2ada8d9,
            0x165fa266, 0x80957705, 0x93cc7314, 0x211a1477,
            0xe6ad2065, 0x77b5fa86, 0xc75442f5, 0xfb9d35cf,
            0xebcdaf0c, 0x7b3e89a0, 0xd6411bd3, 0xae1e7e49,
            0x00250e2d, 0x2071b35e, 0x226800bb, 0x57b8e0af,
            0x2464369b, 0xf009b91e, 0x5563911d, 0x59dfa6aa,
            0x78c14389, 0xd95a537f, 0x207d5ba2, 0x02e5b9c5,
            0x83260376, 0x6295cfa9, 0x11c81968, 0x4e734a41,
            0xb3472dca, 0x7b14a94a, 0x1b510052, 0x9a532915,
            0xd60f573f, 0xbc9bc6e4, 0x2b60a476, 0x81e67400,
            0x08ba6fb5, 0x571be91f, 0xf296ec6b, 0x2a0dd915,
            0xb6636521, 0xe7b9f9b6, 0xff34052e, 0xc5855664,
            0x53b02d5d, 0xa99f8fa1, 0x08ba4799, 0x6e85076a,
            0x4b7a70e9, 0xb5b32944, 0xdb75092e, 0xc4192623,
            0xad6ea6b0, 0x49a7df7d, 0x9cee60b8, 0x8fedb266,
            0xecaa8c71, 0x699a17ff, 0x5664526c, 0xc2b19ee1,
            0x193602a5, 0x75094c29, 0xa0591340, 0xe4183a3e,
            0x3f54989a, 0x5b429d65, 0x6b8fe4d6, 0x99f73fd6,
            0xa1d29c07, 0xefe830f5, 0x4d2d38e6, 0xf0255dc1,
            0x4cdd2086, 0x8470eb26, 0x6382e9c6, 0x021ecc5e,
            0x09686b3f, 0x3ebaefc9, 0x3c971814, 0x6b6a70a1,
            0x687f3584, 0x52a0e286, 0xb79c5305, 0xaa500737,
            0x3e07841c, 0x7fdeae5c, 0x8e7d44ec, 0x5716f2b8,
            0xb03ada37, 0xf0500c0d, 0xf01c1f04, 0x0200b3ff,
            0xae0cf51a, 0x3cb574b2, 0x25837a58, 0xdc0921bd,
            0xd19113f9, 0x7ca92ff6, 0x94324773, 0x22f54701,
            0x3ae5e581, 0x37c2dadc, 0xc8b57634, 0x9af3dda7,
            0xa9446146, 0x0fd0030e, 0xecc8c73e, 0xa4751e41,
            0xe238cd99, 0x3bea0e2f, 0x3280bba1, 0x183eb331,
            0x4e548b38, 0x4f6db908, 0x6f420d03, 0xf60a04bf,
            0x2cb81290, 0x24977c79, 0x5679b072, 0xbcaf89af,
            0xde9a771f, 0xd9930810, 0xb38bae12, 0xdccf3f2e,
            0x5512721f, 0x2e6b7124, 0x501adde6, 0x9f84cd87,
            0x7a584718, 0x7408da17, 0xbc9f9abc, 0xe94b7d8c,
            0xec7aec3a, 0xdb851dfa, 0x63094366, 0xc464c3d2,
            0xef1c1847, 0x3215d908, 0xdd433b37, 0x24c2ba16,
            0x12a14d43, 0x2a65c451, 0x50940002, 0x133ae4dd,
            0x71dff89e, 0x10314e55, 0x81ac77d6, 0x5f11199b,
            0x043556f1, 0xd7a3c76b, 0x3c11183b, 0x5924a509,
            0xf28fe6ed, 0x97f1fbfa, 0x9ebabf2c, 0x1e153c6e,
            0x86e34570, 0xeae96fb1, 0x860e5e0a, 0x5a3e2ab3,
            0x771fe71c, 0x4e3d06fa, 0x2965dcb9, 0x99e71d0f,
            0x803e89d6, 0x5266c825, 0x2e4cc978, 0x9c10b36a,
            0xc6150eba, 0x94e2ea78, 0xa5fc3c53, 0x1e0a2df4,
            0xf2f74ea7, 0x361d2b3d, 0x1939260f, 0x19c27960,
            0x5223a708, 0xf71312b6, 0xebadfe6e, 0xeac31f66,
            0xe3bc4595, 0xa67bc883, 0xb17f37d1, 0x018cff28,
            0xc332ddef, 0xbe6c5aa5, 0x65582185, 0x68ab9802,
            0xeecea50f, 0xdb2f953b, 0x2aef7dad, 0x5b6e2f84,
            0x1521b628, 0x29076170, 0xecdd4775, 0x619f1510,
            0x13cca830, 0xeb61bd96, 0x0334fe1e, 0xaa0363cf,
            0xb5735c90, 0x4c70a239, 0xd59e9e0b, 0xcbaade14,
            0xeecc86bc, 0x60622ca7, 0x9cab5cab, 0xb2f3846e,
            0x648b1eaf, 0x19bdf0ca, 0xa02369b9, 0x655abb50,
            0x40685a32, 0x3c2ab4b3, 0x319ee9d5, 0xc021b8f7,
            0x9b540b19, 0x875fa099, 0x95f7997e, 0x623d7da8,
            0xf837889a, 0x97e32d77, 0x11ed935f, 0x16681281,
            0x0e358829, 0xc7e61fd6, 0x96dedfa1, 0x7858ba99,
            0x57f584a5, 0x1b227263, 0x9b83c3ff, 0x1ac24696,
            0xcdb30aeb, 0x532e3054, 0x8fd948e4, 0x6dbc3128,
            0x58ebf2ef, 0x34c6ffea, 0xfe28ed61, 0xee7c3c73,
            0x5d4a14d9, 0xe864b7e3, 0x42105d14, 0x203e13e0,
            0x45eee2b6, 0xa3aaabea, 0xdb6c4f15, 0xfacb4fd0,
            0xc742f442, 0xef6abbb5, 0x654f3b1d, 0x41cd2105,
            0xd81e799e, 0x86854dc7, 0xe44b476a, 0x3d816250,
            0xcf62a1f2, 0x5b8d2646, 0xfc8883a0, 0xc1c7b6a3,
            0x7f1524c3, 0x69cb7492, 0x47848a0b, 0x5692b285,
            0x095bbf00, 0xad19489d, 0x1462b174, 0x23820e00,
            0x58428d2a, 0x0c55f5ea, 0x1dadf43e, 0x233f7061,
            0x3372f092, 0x8d937e41, 0xd65fecf1, 0x6c223bdb,
            0x7cde3759, 0xcbee7460, 0x4085f2a7, 0xce77326e,
            0xa6078084, 0x19f8509e, 0xe8efd855, 0x61d99735,
            0xa969a7aa, 0xc50c06c2, 0x5a04abfc, 0x800bcadc,
            0x9e447a2e, 0xc3453484, 0xfdd56705, 0x0e1e9ec9,
            0xdb73dbd3, 0x105588cd, 0x675fda79, 0xe3674340,
            0xc5c43465, 0x713e38d8, 0x3d28f89e, 0xf16dff20,
            0x153e21e7, 0x8fb03d4a, 0xe6e39f2b, 0xdb83adf7,
            0xe93d5a68, 0x948140f7, 0xf64c261c, 0x94692934,
            0x411520f7, 0x7602d4f7, 0xbcf46b2e, 0xd4a20068,
            0xd4082471, 0x3320f46a, 0x43b7d4b7, 0x500061af,
            0x1e39f62e, 0x97244546, 0x14214f74, 0xbf8b8840,
            0x4d95fc1d, 0x96b591af, 0x70f4ddd3, 0x66a02f45,
            0xbfbc09ec, 0x03bd9785, 0x7fac6dd0, 0x31cb8504,
            0x96eb27b3, 0x55fd3941, 0xda2547e6, 0xabca0a9a,
            0x28507825, 0x530429f4, 0x0a2c86da, 0xe9b66dfb,
            0x68dc1462, 0xd7486900, 0x680ec0a4, 0x27a18dee,
            0x4f3ffea2, 0xe887ad8c, 0xb58ce006, 0x7af4d6b6,
            0xaace1e7c, 0xd3375fec, 0xce78a399, 0x406b2a42,
            0x20fe9e35, 0xd9f385b9, 0xee39d7ab, 0x3b124e8b,
            0x1dc9faf7, 0x4b6d1856, 0x26a36631, 0xeae397b2,
            0x3a6efa74, 0xdd5b4332, 0x6841e7f7, 0xca7820fb,
            0xfb0af54e, 0xd8feb397, 0x454056ac, 0xba489527,
            0x55533a3a, 0x20838d87, 0xfe6ba9b7, 0xd096954b,
            0x55a867bc, 0xa1159a58, 0xcca92963, 0x99e1db33,
            0xa62a4a56, 0x3f3125f9, 0x5ef47e1c, 0x9029317c,
            0xfdf8e802, 0x04272f70, 0x80bb155c, 0x05282ce3,
            0x95c11548, 0xe4c66d22, 0x48c1133f, 0xc70f86dc,
            0x07f9c9ee, 0x41041f0f, 0x404779a4, 0x5d886e17,
            0x325f51eb, 0xd59bc0d1, 0xf2bcc18f, 0x41113564,
            0x257b7834, 0x602a9c60, 0xdff8e8a3, 0x1f636c1b,
            0x0e12b4c2, 0x02e1329e, 0xaf664fd1, 0xcad18115,
            0x6b2395e0, 0x333e92e1, 0x3b240b62, 0xeebeb922,
            0x85b2a20e, 0xe6ba0d99, 0xde720c8c, 0x2da2f728,
            0xd0127845, 0x95b794fd, 0x647d0862, 0xe7ccf5f0,
            0x5449a36f, 0x877d48fa, 0xc39dfd27, 0xf33e8d1e,
            0x0a476341, 0x992eff74, 0x3a6f6eab, 0xf4f8fd37,
            0xa812dc60, 0xa1ebddf8, 0x991be14c, 0xdb6e6b0d,
            0xc67b5510, 0x6d672c37, 0x2765d43b, 0xdcd0e804,
            0xf1290dc7, 0xcc00ffa3, 0xb5390f92, 0x690fed0b,
            0x667b9ffb, 0xcedb7d9c, 0xa091cf0b, 0xd9155ea3,
            0xbb132f88, 0x515bad24, 0x7b9479bf, 0x763bd6eb,
            0x37392eb3, 0xcc115979, 0x8026e297, 0xf42e312d,
            0x6842ada7, 0xc66a2b3b, 0x12754ccc, 0x782ef11c,
            0x6a124237, 0xb79251e7, 0x06a1bbe6, 0x4bfb6350,
            0x1a6b1018, 0x11caedfa, 0x3d25bdd8, 0xe2e1c3c9,
            0x44421659, 0x0a121386, 0xd90cec6e, 0xd5abea2a,
            0x64af674e, 0xda86a85f, 0xbebfe988, 0x64e4c3fe,
            0x9dbc8057, 0xf0f7c086, 0x60787bf8, 0x6003604d,
            0xd1fd8346, 0xf6381fb0, 0x7745ae04, 0xd736fccc,
            0x83426b33, 0xf01eab71, 0xb0804187, 0x3c005e5f,
            0x77a057be, 0xbde8ae24, 0x55464299, 0xbf582e61,
            0x4e58f48f, 0xf2ddfda2, 0xf474ef38, 0x8789bdc2,
            0x5366f9c3, 0xc8b38e74, 0xb475f255, 0x46fcd9b9,
            0x7aeb2661, 0x8b1ddf84, 0x846a0e79, 0x915f95e2,
            0x466e598e, 0x20b45770, 0x8cd55591, 0xc902de4c,
            0xb90bace1, 0xbb8205d0, 0x11a86248, 0x7574a99e,
            0xb77f19b6, 0xe0a9dc09, 0x662d09a1, 0xc4324633,
            0xe85a1f02, 0x09f0be8c, 0x4a99a025, 0x1d6efe10,
            0x1ab93d1d, 0x0ba5a4df, 0xa186f20f, 0x2868f169,
            0xdcb7da83, 0x573906fe, 0xa1e2ce9b, 0x4fcd7f52,
            0x50115e01, 0xa70683fa, 0xa002b5c4, 0x0de6d027,
            0x9af88c27, 0x773f8641, 0xc3604c06, 0x61a806b5,
            0xf0177a28, 0xc0f586e0, 0x006058aa, 0x30dc7d62,
            0x11e69ed7, 0x2338ea63, 0x53c2dd94, 0xc2c21634,
            0xbbcbee56, 0x90bcb6de, 0xebfc7da1, 0xce591d76,
            0x6f05e409, 0x4b7c0188, 0x39720a3d, 0x7c927c24,
            0x86e3725f, 0x724d9db9, 0x1ac15bb4, 0xd39eb8fc,
            0xed545578, 0x08fca5b5, 0xd83d7cd3, 0x4dad0fc4,
            0x1e50ef5e, 0xb161e6f8, 0xa28514d9, 0x6c51133c,
            0x6fd5c7e7, 0x56e14ec4, 0x362abfce, 0xddc6c837,
            0xd79a3234, 0x92638212, 0x670efa8e, 0x406000e0,
            0x3a39ce37, 0xd3faf5cf, 0xabc27737, 0x5ac52d1b,
            0x5cb0679e, 0x4fa33742, 0xd3822740, 0x99bc9bbe,
            0xd5118e9d, 0xbf0f7315, 0xd62d1c7e, 0xc700c47b,
            0xb78c1b6b, 0x21a19045, 0xb26eb1be, 0x6a366eb4,
            0x5748ab2f, 0xbc946e79, 0xc6a376d2, 0x6549c2c8,
            0x530ff8ee, 0x468dde7d, 0xd5730a1d, 0x4cd04dc6,
            0x2939bbdb, 0xa9ba4650, 0xac9526e8, 0xbe5ee304,
            0xa1fad5f0, 0x6a2d519a, 0x63ef8ce2, 0x9a86ee22,
            0xc089c2b8, 0x43242ef6, 0xa51e03aa, 0x9cf2d0a4,
            0x83c061ba, 0x9be96a4d, 0x8fe51550, 0xba645bd6,
            0x2826a2f9, 0xa73a3ae1, 0x4ba99586, 0xef5562e9,
            0xc72fefd3, 0xf752f7da, 0x3f046f69, 0x77fa0a59,
            0x80e4a915, 0x87b08601, 0x9b09e6ad, 0x3b3ee593,
            0xe990fd5a, 0x9e34d797, 0x2cf0b7d9, 0x022b8b51,
            0x96d5ac3a, 0x017da67d, 0xd1cf3ed6, 0x7c7d2d28,
            0x1f9f25cf, 0xadf2b89b, 0x5ad6b472, 0x5a88f54c,
            0xe029ac71, 0xe019a5e6, 0x47b0acfd, 0xed93fa9b,
            0xe8d3c48d, 0x283b57cc, 0xf8d56629, 0x79132e28,
            0x785f0191, 0xed756055, 0xf7960e44, 0xe3d35e8c,
            0x15056dd4, 0x88f46dba, 0x03a16125, 0x0564f0bd,
            0xc3eb9e15, 0x3c9057a2, 0x97271aec, 0xa93a072a,
            0x1b3f6d9b, 0x1e6321f5, 0xf59c66fb, 0x26dcf319,
            0x7533d928, 0xb155fdf5, 0x03563482, 0x8aba3cbb,
            0x28517711, 0xc20ad9f8, 0xabcc5167, 0xccad925f,
            0x4de81751, 0x3830dc8e, 0x379d5862, 0x9320f991,
            0xea7a90c2, 0xfb3e7bce, 0x5121ce64, 0x774fbe32,
            0xa8b6e37e, 0xc3293d46, 0x48de5369, 0x6413e680,
            0xa2ae0810, 0xdd6db224, 0x69852dfd, 0x09072166,
            0xb39a460a, 0x6445c0dd, 0x586cdecf, 0x1c20c8ae,
            0x5bbef7dd, 0x1b588d40, 0xccd2017f, 0x6bb4e3bb,
            0xdda26a7e, 0x3a59ff45, 0x3e350a44, 0xbcb4cdd5,
            0x72eacea8, 0xfa6484bb, 0x8d6612ae, 0xbf3c6f47,
            0xd29be463, 0x542f5d9e, 0xaec2771b, 0xf64e6370,
            0x740e0d8d, 0xe75b1357, 0xf8721671, 0xaf537d5d,
            0x4040cb08, 0x4eb4e2cc, 0x34d2466a, 0x0115af84,
            0xe1b00428, 0x95983a1d, 0x06b89fb4, 0xce6ea048,
            0x6f3f3b82, 0x3520ab82, 0x011a1d4b, 0x277227f8,
            0x611560b1, 0xe7933fdc, 0xbb3a792b, 0x344525bd,
            0xa08839e1, 0x51ce794b, 0x2f32c9b7, 0xa01fbac9,
            0xe01cc87e, 0xbcc7d1f6, 0xcf0111c3, 0xa1e8aac7,
            0x1a908749, 0xd44fbd9a, 0xd0dadecb, 0xd50ada38,
            0x0339c32a, 0xc6913667, 0x8df9317c, 0xe0b12b4f,
            0xf79e59b7, 0x43f5bb3a, 0xf2d519ff, 0x27d9459c,
            0xbf97222c, 0x15e6fc2a, 0x0f91fc71, 0x9b941525,
            0xfae59361, 0xceb69ceb, 0xc2a86459, 0x12baa8d1,
            0xb6c1075e, 0xe3056a0c, 0x10d25065, 0xcb03a442,
            0xe0ec6e0e, 0x1698db3b, 0x4c98a0be, 0x3278e964,
            0x9f1f9532, 0xe0d392df, 0xd3a0342b, 0x8971f21e,
            0x1b0a7441, 0x4ba3348c, 0xc5be7120, 0xc37632d8,
            0xdf359f8d, 0x9b992f2e, 0xe60b6f47, 0x0fe3f11d,
            0xe54cda54, 0x1edad891, 0xce6279cf, 0xcd3e7e6f,
            0x1618b166, 0xfd2c1d05, 0x848fd2c5, 0xf6fb2299,
            0xf523f357, 0xa6327623, 0x93a83531, 0x56cccd02,
            0xacf08162, 0x5a75ebb5, 0x6e163697, 0x88d273cc,
            0xde966292, 0x81b949d0, 0x4c50901b, 0x71c65614,
            0xe6c6c7bd, 0x327a140a, 0x45e1d006, 0xc3f27b9a,
            0xc9aa53fd, 0x62a80f00, 0xbb25bfe2, 0x35bdd2f6,
            0x71126905, 0xb2040222, 0xb6cbcf7c, 0xcd769c2b,
            0x53113ec0, 0x1640e3d3, 0x38abbd60, 0x2547adf0,
            0xba38209c, 0xf746ce76, 0x77afa1c5, 0x20756060,
            0x85cbfe4e, 0x8ae88dd8, 0x7aaaf9b0, 0x4cf9aa7e,
            0x1948c25c, 0x02fb8a8c, 0x01c36ae4, 0xd6ebe1f9,
            0x90d4f869, 0xa65cdea0, 0x3f09252d, 0xc208e69f,
            0xb74e6132, 0xce77e25b, 0x578fdfe3, 0x3ac372e6
        };

        // OpenBSD IV: "OxychromaticBlowfishSwatDynamite" in big endian
        private static readonly uint[] _OpenBsdIv = new uint[] {
            0x4f787963, 0x68726f6d, 0x61746963, 0x426c6f77,
            0x66697368, 0x53776174, 0x44796e61, 0x6d697465,
        };

        // bcrypt IV: "OrpheanBeholderScryDoubt"
        private static readonly uint[] _BfCryptCiphertext = {
            0x4f727068, 0x65616e42, 0x65686f6c,
            0x64657253, 0x63727944, 0x6f756274
        };

        // Table for Base64 encoding
        private static readonly char[] _Base64Code = {
            '.', '/', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
            'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
            'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
            'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
            'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5',
            '6', '7', '8', '9'
        };

        // Table for Base64 decoding
        private static readonly int[] _Index64 = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, 0, 1, 54, 55,
            56, 57, 58, 59, 60, 61, 62, 63, -1, -1,
            -1, -1, -1, -1, -1, 2, 3, 4, 5, 6,
            7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
            17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
            -1, -1, -1, -1, -1, -1, 28, 29, 30,
            31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
            51, 52, 53, -1, -1, -1, -1, -1
        };

        // Expanded Blowfish key
        private uint[] _P;
        private uint[] _S;

        /// <summary>
        ///  Hash a string using the OpenBSD bcrypt scheme and a salt generated by <see
        ///  cref="BCrypt.GenerateSalt()"/>.
        /// </summary>
        /// <remarks>Just an alias for HashPassword.</remarks>
        /// <param name="source">The string to hash.</param>
        /// <returns>The hashed string.</returns>
        public static string HashString(string source)
        {
            return HashPassword(source);
        }

        /// <summary>
        ///  Hash a string using the OpenBSD bcrypt scheme and a salt generated by <see
        ///  cref="BCrypt.GenerateSalt()"/>.
        /// </summary>
        /// <remarks>Just an alias for HashPassword.</remarks>
        /// <param name="source">  The string to hash.</param>
        /// <param name="workFactor">The log2 of the number of rounds of hashing to apply - the work
        ///                          factor therefore increases as 2^workFactor.</param>
        /// <returns>The hashed string.</returns>
        public static string HashString(string source, int workFactor)
        {
            return HashPassword(source, GenerateSalt(workFactor));
        }

        /// <summary>
        ///  Hash a password using the OpenBSD bcrypt scheme and a salt generated by <see
        ///  cref="BCrypt.GenerateSalt()"/>.
        /// </summary>
        /// <param name="input">The password to hash.</param>
        /// <returns>The hashed password.</returns>
        public static string HashPassword(string input)
        {
            return HashPassword(input, GenerateSalt());
        }

        /// <summary>
        ///  Hash a password using the OpenBSD bcrypt scheme and a salt generated by <see
        ///  cref="BCrypt.GenerateSalt(int)"/> using the given <paramref name="workFactor"/>.
        /// </summary>
        /// <param name="input">     The password to hash.</param>
        /// <param name="workFactor">The log2 of the number of rounds of hashing to apply - the work
        ///                          factor therefore increases as 2^workFactor.</param>
        /// <returns>The hashed password.</returns>
        public static string HashPassword(string input, int workFactor)
        {
            return HashPassword(input, GenerateSalt(workFactor));
        }

        /// <summary>Hash a password using the OpenBSD bcrypt scheme.</summary>
        /// <exception cref="ArgumentException">Thrown when one or more arguments have unsupported or
        ///                                     illegal values.</exception>
        /// <param name="input">The password to hash.</param>
        /// <param name="salt">    the salt to hash with (perhaps generated using BCrypt.gensalt).</param>
        /// <returns>The hashed password</returns>
        public static string HashPassword(string input, string salt)
        {
            if (input == null)
                throw new ArgumentNullException("input");

            if (string.IsNullOrEmpty(salt))
                throw new ArgumentException("Invalid salt", "salt");

            // Determinthe starting offset and validate the salt
            int startingOffset;
            char minor = (char)0;
            if (salt[0] != '$' || salt[1] != '2')
                throw new SaltParseException("Invalid salt version");
            if (salt[2] == '$')
                startingOffset = 3;
            else
            {
                minor = salt[2];
                if (minor != 'a' || salt[3] != '$')
                    throw new SaltParseException("Invalid salt revision");
                startingOffset = 4;
            }

            // Extract number of rounds
            if (salt[startingOffset + 2] > '$')
                throw new SaltParseException("Missing salt rounds");

            // Extract details from salt
            int logRounds = Convert.ToInt32(salt.Substring(startingOffset, 2));
            string extractedSalt = salt.Substring(startingOffset + 3, 22);

            byte[] inputBytes = Encoding.UTF8.GetBytes((input + (minor >= 'a' ? "\0" : "")));
            byte[] saltBytes = DecodeBase64(extractedSalt, BCRYPT_SALT_LEN);

            BCrypt bCrypt = new BCrypt();
            byte[] hashed = bCrypt.CryptRaw(inputBytes, saltBytes, logRounds);

            // Generate result string
            StringBuilder result = new StringBuilder();
            result.Append("$2");
            if (minor >= 'a')
                result.Append(minor);
            result.AppendFormat("${0:00}$", logRounds);
            result.Append(EncodeBase64(saltBytes, saltBytes.Length));
            result.Append(EncodeBase64(hashed, (_BfCryptCiphertext.Length * 4) - 1));
            return result.ToString();
        }

        /// <summary>
        ///  Generate a salt for use with the <see cref="BCrypt.HashPassword(string,string)"/> method.
        /// </summary>
        /// <param name="workFactor">The log2 of the number of rounds of hashing to apply - the work
        ///                          factor therefore increases as 2**workFactor.</param>
        /// <returns>A base64 encoded salt value.</returns>
        public static string GenerateSalt(int workFactor)
        {
            if (workFactor < 4 || workFactor > 31)
                throw new ArgumentOutOfRangeException("workFactor", "The work factor must be between 4 and 31 (inclusive)");

            byte[] rnd = new byte[BCRYPT_SALT_LEN];

            RandomNumberGenerator rng = RandomNumberGenerator.Create();

            rng.GetBytes(rnd);

            StringBuilder rs = new StringBuilder();
            rs.AppendFormat("$2a${0:00}$", workFactor);
            rs.Append(EncodeBase64(rnd, rnd.Length));
            return rs.ToString();
        }

        /// <summary>
        ///  Generate a salt for use with the <see cref="BCrypt.HashPassword(string,string)"/> method
        ///  selecting a reasonable default for the number of hashing rounds to apply.
        /// </summary>
        /// <returns>A base64 encoded salt value.</returns>
        public static string GenerateSalt()
        {
            return GenerateSalt(GENSALT_DEFAULT_LOG2_ROUNDS);
        }

        /// <summary>
        ///  Verifies that the hash of the given <paramref name="text"/> matches the provided
        ///  <paramref name="hash"/>
        /// </summary>
        /// <param name="text">The text to verify.</param>
        /// <param name="hash"> The previously-hashed password.</param>
        /// <returns>true if the passwords match, false otherwise.</returns>
        public static bool Verify(string text, string hash)
        {
            return hash == HashPassword(text, hash);
        }

        /// <summary>
        ///  Encode a byte array using bcrypt's slightly-modified base64 encoding scheme. Note that this
        ///  is *not* compatible with the standard MIME-base64 encoding.
        /// </summary>
        /// <exception cref="ArgumentException">Thrown when one or more arguments have unsupported or
        ///                                     illegal values.</exception>
        /// <param name="byteArray">The byte array to encode.</param>
        /// <param name="length">   The number of bytes to encode.</param>
        /// <returns>Base64-encoded string.</returns>
        private static string EncodeBase64(byte[] byteArray, int length)
        {
            if (length <= 0 || length > byteArray.Length)
                throw new ArgumentException("Invalid length", "length");

            int off = 0;
            StringBuilder rs = new StringBuilder();
            while (off < length)
            {
                int c1 = byteArray[off++] & 0xff;
                rs.Append(_Base64Code[(c1 >> 2) & 0x3f]);
                c1 = (c1 & 0x03) << 4;
                if (off >= length)
                {
                    rs.Append(_Base64Code[c1 & 0x3f]);
                    break;
                }
                int c2 = byteArray[off++] & 0xff;
                c1 |= (c2 >> 4) & 0x0f;
                rs.Append(_Base64Code[c1 & 0x3f]);
                c1 = (c2 & 0x0f) << 2;
                if (off >= length)
                {
                    rs.Append(_Base64Code[c1 & 0x3f]);
                    break;
                }
                c2 = byteArray[off++] & 0xff;
                c1 |= (c2 >> 6) & 0x03;
                rs.Append(_Base64Code[c1 & 0x3f]);
                rs.Append(_Base64Code[c2 & 0x3f]);
            }
            return rs.ToString();
        }

        /// <summary>
        ///  Decode a string encoded using bcrypt's base64 scheme to a byte array. Note that this is *not*
        ///  compatible with the standard MIME-base64 encoding.
        /// </summary>
        /// <exception cref="ArgumentException">Thrown when one or more arguments have unsupported or
        ///                                     illegal values.</exception>
        /// <param name="encodedstring">The string to decode.</param>
        /// <param name="maximumBytes"> The maximum bytes to decode.</param>
        /// <returns>The decoded byte array.</returns>
        private static byte[] DecodeBase64(string encodedstring, int maximumBytes)
        {
            int position = 0,
                sourceLength = encodedstring.Length,
                outputLength = 0;

            if (maximumBytes <= 0)
                throw new ArgumentException("Invalid maximum bytes value", "maximumBytes");

            // TODO: update to use a List<byte> - it's only ever 16 bytes, so it's not a big deal
            StringBuilder rs = new StringBuilder();
            while (position < sourceLength - 1 && outputLength < maximumBytes)
            {
                int c1 = Char64(encodedstring[position++]);
                int c2 = Char64(encodedstring[position++]);
                if (c1 == -1 || c2 == -1)
                    break;

                rs.Append((char)((c1 << 2) | ((c2 & 0x30) >> 4)));
                if (++outputLength >= maximumBytes || position >= sourceLength)
                    break;

                int c3 = Char64(encodedstring[position++]);
                if (c3 == -1)
                    break;

                rs.Append((char)(((c2 & 0x0f) << 4) | ((c3 & 0x3c) >> 2)));
                if (++outputLength >= maximumBytes || position >= sourceLength)
                    break;

                int c4 = Char64(encodedstring[position++]);
                rs.Append((char)(((c3 & 0x03) << 6) | c4));

                ++outputLength;
            }

            byte[] ret = new byte[outputLength];
            for (position = 0; position < outputLength; position++)
                ret[position] = (byte)rs[position];
            return ret;
        }

        /// <summary>
        ///  Look up the 3 bits base64-encoded by the specified character, range-checking against
        ///  conversion table.
        /// </summary>
        /// <param name="character">The base64-encoded value.</param>
        /// <returns>The decoded value of x.</returns>
        private static int Char64(char character)
        {
            if (character < 0 || character > _Index64.Length)
                return -1;
            return _Index64[character];
        }

        /// <summary>Blowfish encipher a single 64-bit block encoded as two 32-bit halves.</summary>
        /// <param name="blockArray">An array containing the two 32-bit half blocks.</param>
        /// <param name="offset">    The position in the array of the blocks.</param>
        private void Encipher(uint[] blockArray, int offset)
        {
            uint round,
                     n,
                     block = blockArray[offset],
                     r = blockArray[offset + 1];

            block ^= _P[0];
            for (round = 0; round <= BLOWFISH_NUM_ROUNDS - 2;)
            {
                // Feistel substitution on left word
                n = _S[(block >> 24) & 0xff];
                n += _S[0x100 | ((block >> 16) & 0xff)];
                n ^= _S[0x200 | ((block >> 8) & 0xff)];
                n += _S[0x300 | (block & 0xff)];
                r ^= n ^ _P[++round];

                // Feistel substitution on right word
                n = _S[(r >> 24) & 0xff];
                n += _S[0x100 | ((r >> 16) & 0xff)];
                n ^= _S[0x200 | ((r >> 8) & 0xff)];
                n += _S[0x300 | (r & 0xff)];
                block ^= n ^ _P[++round];
            }
            blockArray[offset] = r ^ _P[BLOWFISH_NUM_ROUNDS + 1];
            blockArray[offset + 1] = block;
        }

        /// <summary>Cycically extract a word of key material.</summary>
        /// <param name="data">The string to extract the data from.</param>
        /// <param name="offset"> [in,out] The current offset.</param>
        /// <returns>The next word of material from data.</returns>
        private static uint StreamToWord(byte[] data, ref int offset)
        {
            int i;
            uint word = 0;

            for (i = 0; i < 4; i++)
            {
                word = (word << 8) | (uint)(data[offset] & 0xff);
                offset = (offset + 1) % data.Length;
            }
            return word;
        }

        /// <summary>Initializes the Blowfish key schedule.</summary>
        private void InitializeKey()
        {
            _P = new uint[_POrig.Length];
            _S = new uint[_SOrig.Length];
            Array.Copy(_POrig, _P, _POrig.Length);
            Array.Copy(_SOrig, _S, _SOrig.Length);
        }

        /// <summary>Key the Blowfish cipher.</summary>
        /// <param name="keyBytes">The key byte array.</param>
        private void Key(byte[] keyBytes)
        {
            int i;
            int koffp = 0;
            uint[] lr = { 0, 0 };
            int plen = _P.Length, slen = _S.Length;

            for (i = 0; i < plen; i++)
                _P[i] = _P[i] ^ StreamToWord(keyBytes, ref koffp);

            for (i = 0; i < plen; i += 2)
            {
                Encipher(lr, 0);
                _P[i] = lr[0];
                _P[i + 1] = lr[1];
            }

            for (i = 0; i < slen; i += 2)
            {
                Encipher(lr, 0);
                _S[i] = lr[0];
                _S[i + 1] = lr[1];
            }
        }

        /// <summary>
        ///  Perform the "enhanced key schedule" step described by Provos and Mazieres in "A Future-
        ///  Adaptable Password Scheme" http://www.openbsd.org/papers/bcrypt-paper.ps.
        /// </summary>
        /// <param name="saltBytes"> Salt byte array.</param>
        /// <param name="inputBytes">Input byte array.</param>
        private void EKSKey(byte[] saltBytes, byte[] inputBytes)
        {
            int i;
            int passwordOffset = 0,
                saltOffset = 0;
            uint[] lr = { 0, 0 };
            int plen = _P.Length, slen = _S.Length;

            for (i = 0; i < plen; i++)
                _P[i] = _P[i] ^ StreamToWord(inputBytes, ref passwordOffset);

            for (i = 0; i < plen; i += 2)
            {
                lr[0] ^= StreamToWord(saltBytes, ref saltOffset);
                lr[1] ^= StreamToWord(saltBytes, ref saltOffset);
                Encipher(lr, 0);
                _P[i] = lr[0];
                _P[i + 1] = lr[1];
            }

            for (i = 0; i < slen; i += 2)
            {
                lr[0] ^= StreamToWord(saltBytes, ref saltOffset);
                lr[1] ^= StreamToWord(saltBytes, ref saltOffset);
                Encipher(lr, 0);
                _S[i] = lr[0];
                _S[i + 1] = lr[1];
            }
        }

        /// <summary>Perform the central hashing step in the bcrypt scheme.</summary>
        /// <exception cref="ArgumentException">Thrown when one or more arguments have unsupported or
        ///                                     illegal values.</exception>
        /// <param name="inputBytes">The input byte array to hash.</param>
        /// <param name="saltBytes"> The salt byte array to hash with.</param>
        /// <param name="logRounds"> The binary logarithm of the number of rounds of hashing to apply.</param>
        /// <returns>A byte array containing the hashed result.</returns>
        private byte[] CryptRaw(byte[] inputBytes, byte[] saltBytes, int logRounds)
        {
            uint[] cdata = new uint[_BfCryptCiphertext.Length];
            Array.Copy(_BfCryptCiphertext, cdata, _BfCryptCiphertext.Length);
            int clen = cdata.Length;

            if (logRounds < 4 || logRounds > 31)
                throw new ArgumentException("Bad number of rounds", "logRounds");

            if (saltBytes.Length != BCRYPT_SALT_LEN)
                throw new ArgumentException("Bad salt Length", "saltBytes");

            uint rounds = 1u << logRounds;
            Debug.Assert(rounds > 0, "Rounds must be > 0"); // We overflowed rounds at 31 - added safety check

            InitializeKey();
            EKSKey(saltBytes, inputBytes);

            for (int i = 0; i < rounds; i++)
            {
                Key(inputBytes);
                Key(saltBytes);
            }

            for (int i = 0; i < 64; i++)
            {
                for (int j = 0; j < (clen >> 1); j++)
                    Encipher(cdata, j << 1);
            }

            byte[] ret = new byte[clen * 4];
            for (int i = 0, j = 0; i < clen; i++)
            {
                ret[j++] = (byte)((cdata[i] >> 24) & 0xff);
                ret[j++] = (byte)((cdata[i] >> 16) & 0xff);
                ret[j++] = (byte)((cdata[i] >> 8) & 0xff);
                ret[j++] = (byte)(cdata[i] & 0xff);
            }
            return ret;
        }

        /**
         * Compatibility with new OpenBSD function.
         * Ported from SSHJ library (https://github.com/hierynomus/sshj)
         */
        public void Hash(byte[] hpass, byte[] hsalt, byte[] output)
        {
            InitializeKey();
            EKSKey(hsalt, hpass);
            for (int i = 0; i < 64; i++)
            {
                Key(hsalt);
                Key(hpass);
            }

            uint[] buf = new uint[_OpenBsdIv.Length];
            Array.Copy(_OpenBsdIv, 0, buf, 0, _OpenBsdIv.Length);
            for (int i = 0; i < 8; i += 2)
            {
                for (int j = 0; j < 64; j++)
                {
                    Encipher(buf, i);
                }
            }

            for (int i = 0, j = 0; i < buf.Length; i++)
            {
                // Output of this is little endian
                output[j++] = (byte)(buf[i] & 0xff);
                output[j++] = (byte)((buf[i] >> 8) & 0xff);
                output[j++] = (byte)((buf[i] >> 16) & 0xff);
                output[j++] = (byte)((buf[i] >> 24) & 0xff);
            }
        }

        /// <summary>
        /// Applies the Bcrypt kdf to derive a key and iv from the passphrase, 
        /// the key/iv are returned in the output variable.
        /// Ported from the SSHJ library. https://github.com/hierynomus/sshj
        /// </summary>
        /// <param name="password"></param>
        /// <param name="salt"></param>
        /// <param name="rounds"></param>
        /// <param name="output"></param>
        public void Pbkdf(byte[] password, byte[] salt, int rounds, byte[] output)
        {
            using (var sha512 = CryptoAbstraction.CreateSHA512())
            {
                int nblocks = (output.Length + 31) / 32;
                byte[] hpass = sha512.ComputeHash(password);

                byte[] hsalt = new byte[64];
                byte[] block_b = new byte[4];
                byte[] outBytes = new byte[32];
                byte[] tmp = new byte[32];
                for (int block = 1; block <= nblocks; block++)
                {
                    // Block count is in big endian
                    block_b[0] = (byte)((block >> 24) & 0xFF);
                    block_b[1] = (byte)((block >> 16) & 0xFF);
                    block_b[2] = (byte)((block >> 8) & 0xFF);
                    block_b[3] = (byte)(block & 0xFF);

                    hsalt = sha512.ComputeHash(AppendArrays(salt, block_b));
                    Hash(hpass, hsalt, outBytes);
                    Array.Copy(outBytes, 0, tmp, 0, outBytes.Length);

                    for (int round = 1; round < rounds; round++)
                    {
                        hsalt = sha512.ComputeHash(tmp);
                        Hash(hpass, hsalt, tmp);

                        for (int i = 0; i < tmp.Length; i++)
                        {
                            outBytes[i] ^= tmp[i];
                        }
                    }

                    for (int i = 0; i < outBytes.Length; i++)
                    {
                        int idx = i * nblocks + (block - 1);
                        if (idx < output.Length)
                        {
                            output[idx] = outBytes[i];
                        }
                    }
                }
            }
        }

        /// <summary>
        /// Appends multiple byte arrays into one array.
        /// </summary>
        /// <param name="b1"></param>
        /// <param name="others"></param>
        /// <returns></returns>
        private byte[] AppendArrays(byte[] b1, params byte[][] others)
        {
            //from https://stackoverflow.com/questions/46534429/how-to-convert-java-messagedigest-with-two-update-statements-to-c-sharp
            int n = b1.Length;
            foreach (var other in others)
            {
                n += other.Length;
            }

            var result = new byte[n];

            n = 0;
            Array.Copy(b1, 0, result, n, b1.Length);
            n += b1.Length;
            foreach (var other in others)
            {
                Array.Copy(other, 0, result, n, other.Length);
                n += other.Length;
            }

            return result;
        }

        /// <summary>Exception for signalling parse errors. </summary>
        public class SaltParseException : Exception
        {
            /// <summary>Default constructor. </summary>
            public SaltParseException()
            {
            }

            /// <summary>Initializes a new instance of <see cref="SaltParseException"/>.</summary>
            /// <param name="message">The message.</param>
            public SaltParseException(string message)
                : base(message)
            {
            }

            /// <summary>Initializes a new instance of <see cref="SaltParseException"/>.</summary>
            /// <param name="message">       The message.</param>
            /// <param name="innerException">The inner exception.</param>
            public SaltParseException(string message, Exception innerException)
                : base(message, innerException)
            {
            }
        }
    }
}