const std = @import("std");
const crypto = std.crypto;
const debug = std.debug;
const fmt = std.fmt;
const math = std.math;
const mem = std.mem;
const pwhash = crypto.pwhash;
const testing = std.testing;
const utils = crypto.utils;

const phc_format = @import("phc_encoding.zig");

const KdfError = pwhash.KdfError;
const HasherError = pwhash.HasherError;
const EncodingError = phc_format.Error;
const Error = pwhash.Error;

const salt_length: usize = 16;
const salt_str_length: usize = 22;
const ct_str_length: usize = 31;
const ct_length: usize = 24;
const dk_length: usize = ct_length - 1;

/// Length (in bytes) of a password hash in crypt encoding
pub const hash_length: usize = 60;

const State = struct {
    sboxes: [4][256]u32 = [4][256]u32{
        .{
            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,
        },
    },
    subkeys: [18]u32 = [18]u32{
        0x243f6a88, 0x85a308d3, 0x13198a2e,
        0x03707344, 0xa4093822, 0x299f31d0,
        0x082efa98, 0xec4e6c89, 0x452821e6,
        0x38d01377, 0xbe5466cf, 0x34e90c6c,
        0xc0ac29b7, 0xc97c50dd, 0x3f84d5b5,
        0xb5470917, 0x9216d5d9, 0x8979fb1b,
    },

    fn toWord(data: []const u8, current: *usize) u32 {
        var t: u32 = 0;
        var j = current.*;
        var i: usize = 0;
        while (i < 4) : (i += 1) {
            if (j >= data.len) j = 0;
            t = (t << 8) | data[j];
            j += 1;
        }
        current.* = j;
        return t;
    }

    fn expand0(state: *State, key: []const u8) void {
        var i: usize = 0;
        var j: usize = 0;
        while (i < state.subkeys.len) : (i += 1) {
            state.subkeys[i] ^= toWord(key, &j);
        }

        var halves = Halves{ .l = 0, .r = 0 };
        i = 0;
        while (i < 18) : (i += 2) {
            state.encipher(&halves);
            state.subkeys[i] = halves.l;
            state.subkeys[i + 1] = halves.r;
        }

        i = 0;
        while (i < 4) : (i += 1) {
            var k: usize = 0;
            while (k < 256) : (k += 2) {
                state.encipher(&halves);
                state.sboxes[i][k] = halves.l;
                state.sboxes[i][k + 1] = halves.r;
            }
        }
    }

    fn expand(state: *State, data: []const u8, key: []const u8) void {
        var i: usize = 0;
        var j: usize = 0;
        while (i < state.subkeys.len) : (i += 1) {
            state.subkeys[i] ^= toWord(key, &j);
        }

        var halves = Halves{ .l = 0, .r = 0 };
        i = 0;
        j = 0;
        while (i < 18) : (i += 2) {
            halves.l ^= toWord(data, &j);
            halves.r ^= toWord(data, &j);
            state.encipher(&halves);
            state.subkeys[i] = halves.l;
            state.subkeys[i + 1] = halves.r;
        }

        i = 0;
        while (i < 4) : (i += 1) {
            var k: usize = 0;
            while (k < 256) : (k += 2) {
                halves.l ^= toWord(data, &j);
                halves.r ^= toWord(data, &j);
                state.encipher(&halves);
                state.sboxes[i][k] = halves.l;
                state.sboxes[i][k + 1] = halves.r;
            }
        }
    }

    const Halves = struct { l: u32, r: u32 };

    fn feistelF(state: State, x: u32) u32 {
        var r = state.sboxes[0][@truncate(u8, x >> 24)];
        r +%= state.sboxes[1][@truncate(u8, x >> 16)];
        r ^= state.sboxes[2][@truncate(u8, x >> 8)];
        r +%= state.sboxes[3][@truncate(u8, x)];
        return r;
    }

    fn halfRound(state: State, i: u32, j: u32, n: usize) u32 {
        return i ^ state.feistelF(j) ^ state.subkeys[n];
    }

    fn encipher(state: State, halves: *Halves) void {
        halves.l ^= state.subkeys[0];
        var i: usize = 1;
        while (i < 16) : (i += 2) {
            halves.r = state.halfRound(halves.r, halves.l, i);
            halves.l = state.halfRound(halves.l, halves.r, i + 1);
        }
        const halves_last = Halves{ .l = halves.r ^ state.subkeys[i], .r = halves.l };
        halves.* = halves_last;
    }

    fn encrypt(state: State, data: []u32) void {
        debug.assert(data.len % 2 == 0);
        var i: usize = 0;
        while (i < data.len) : (i += 2) {
            var halves = Halves{ .l = data[i], .r = data[i + 1] };
            state.encipher(&halves);
            data[i] = halves.l;
            data[i + 1] = halves.r;
        }
    }
};

pub const Params = struct {
    rounds_log: u6,
};

pub fn bcrypt(
    password: []const u8,
    salt: [salt_length]u8,
    params: Params,
) [dk_length]u8 {
    var state = State{};
    var password_buf: [73]u8 = undefined;
    const trimmed_len = math.min(password.len, password_buf.len - 1);
    mem.copy(u8, password_buf[0..], password[0..trimmed_len]);
    password_buf[trimmed_len] = 0;
    var passwordZ = password_buf[0 .. trimmed_len + 1];
    state.expand(salt[0..], passwordZ);

    const rounds: u64 = @as(u64, 1) << params.rounds_log;
    var k: u64 = 0;
    while (k < rounds) : (k += 1) {
        state.expand0(passwordZ);
        state.expand0(salt[0..]);
    }
    utils.secureZero(u8, &password_buf);

    var cdata = [6]u32{ 0x4f727068, 0x65616e42, 0x65686f6c, 0x64657253, 0x63727944, 0x6f756274 }; // "OrpheanBeholderScryDoubt"
    k = 0;
    while (k < 64) : (k += 1) {
        state.encrypt(&cdata);
    }

    var ct: [ct_length]u8 = undefined;
    for (cdata) |c, i| {
        mem.writeIntBig(u32, ct[i * 4 ..][0..4], c);
    }
    return ct[0..dk_length].*;
}

const crypt_format = struct {
    /// String prefix for bcrypt
    pub const prefix = "$2";

    // bcrypt has its own variant of base64, with its own alphabet and no padding
    const Codec = struct {
        const alphabet = "./ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

        fn encode(b64: []u8, bin: []const u8) void {
            var i: usize = 0;
            var j: usize = 0;
            while (i < bin.len) {
                var c1 = bin[i];
                i += 1;
                b64[j] = alphabet[c1 >> 2];
                j += 1;
                c1 = (c1 & 3) << 4;
                if (i >= bin.len) {
                    b64[j] = alphabet[c1];
                    j += 1;
                    break;
                }
                var c2 = bin[i];
                i += 1;
                c1 |= (c2 >> 4) & 0x0f;
                b64[j] = alphabet[c1];
                j += 1;
                c1 = (c2 & 0x0f) << 2;
                if (i >= bin.len) {
                    b64[j] = alphabet[c1];
                    j += 1;
                    break;
                }
                c2 = bin[i];
                i += 1;
                c1 |= (c2 >> 6) & 3;
                b64[j] = alphabet[c1];
                b64[j + 1] = alphabet[c2 & 0x3f];
                j += 2;
            }
            debug.assert(j == b64.len);
        }

        fn decode(bin: []u8, b64: []const u8) EncodingError!void {
            var i: usize = 0;
            var j: usize = 0;
            while (j < bin.len) {
                const c1 = @intCast(u8, mem.indexOfScalar(u8, alphabet, b64[i]) orelse
                    return EncodingError.InvalidEncoding);
                const c2 = @intCast(u8, mem.indexOfScalar(u8, alphabet, b64[i + 1]) orelse
                    return EncodingError.InvalidEncoding);
                bin[j] = (c1 << 2) | ((c2 & 0x30) >> 4);
                j += 1;
                if (j >= bin.len) {
                    break;
                }
                const c3 = @intCast(u8, mem.indexOfScalar(u8, alphabet, b64[i + 2]) orelse
                    return EncodingError.InvalidEncoding);
                bin[j] = ((c2 & 0x0f) << 4) | ((c3 & 0x3c) >> 2);
                j += 1;
                if (j >= bin.len) {
                    break;
                }
                const c4 = @intCast(u8, mem.indexOfScalar(u8, alphabet, b64[i + 3]) orelse
                    return EncodingError.InvalidEncoding);
                bin[j] = ((c3 & 0x03) << 6) | c4;
                j += 1;
                i += 4;
            }
        }
    };

    fn strHashInternal(
        password: []const u8,
        salt: [salt_length]u8,
        params: Params,
    ) [hash_length]u8 {
        var dk = bcrypt(password, salt, params);

        var salt_str: [salt_str_length]u8 = undefined;
        Codec.encode(salt_str[0..], salt[0..]);

        var ct_str: [ct_str_length]u8 = undefined;
        Codec.encode(ct_str[0..], dk[0..]);

        var s_buf: [hash_length]u8 = undefined;
        const s = fmt.bufPrint(
            s_buf[0..],
            "{s}b${d}{d}${s}{s}",
            .{ prefix, params.rounds_log / 10, params.rounds_log % 10, salt_str, ct_str },
        ) catch unreachable;
        debug.assert(s.len == s_buf.len);
        return s_buf;
    }
};

/// Hash and verify passwords using the PHC format.
const PhcFormatHasher = struct {
    const alg_id = "bcrypt";
    const BinValue = phc_format.BinValue;

    const HashResult = struct {
        alg_id: []const u8,
        r: u6,
        salt: BinValue(salt_length),
        hash: BinValue(dk_length),
    };

    /// Return a non-deterministic hash of the password encoded as a PHC-format string
    pub fn create(
        password: []const u8,
        params: Params,
        buf: []u8,
    ) HasherError![]const u8 {
        var salt: [salt_length]u8 = undefined;
        crypto.random.bytes(&salt);

        const hash = bcrypt(password, salt, params);

        return phc_format.serialize(HashResult{
            .alg_id = alg_id,
            .r = params.rounds_log,
            .salt = try BinValue(salt_length).fromSlice(&salt),
            .hash = try BinValue(dk_length).fromSlice(&hash),
        }, buf);
    }

    /// Verify a password against a PHC-format encoded string
    pub fn verify(
        str: []const u8,
        password: []const u8,
    ) HasherError!void {
        const hash_result = try phc_format.deserialize(HashResult, str);

        if (!mem.eql(u8, hash_result.alg_id, alg_id)) return HasherError.PasswordVerificationFailed;
        if (hash_result.salt.len != salt_length or hash_result.hash.len != dk_length)
            return HasherError.InvalidEncoding;

        const hash = bcrypt(password, hash_result.salt.buf, .{ .rounds_log = hash_result.r });
        const expected_hash = hash_result.hash.constSlice();

        if (!mem.eql(u8, &hash, expected_hash)) return HasherError.PasswordVerificationFailed;
    }
};

/// Hash and verify passwords using the modular crypt format.
const CryptFormatHasher = struct {
    /// Length of a string returned by the create() function
    pub const pwhash_str_length: usize = hash_length;

    /// Return a non-deterministic hash of the password encoded into the modular crypt format
    pub fn create(
        password: []const u8,
        params: Params,
        buf: []u8,
    ) HasherError![]const u8 {
        if (buf.len < pwhash_str_length) return HasherError.NoSpaceLeft;

        var salt: [salt_length]u8 = undefined;
        crypto.random.bytes(&salt);

        const hash = crypt_format.strHashInternal(password, salt, params);
        mem.copy(u8, buf, &hash);

        return buf[0..pwhash_str_length];
    }

    /// Verify a password against a string in modular crypt format
    pub fn verify(
        str: []const u8,
        password: []const u8,
    ) HasherError!void {
        if (str.len != pwhash_str_length or str[3] != '$' or str[6] != '$')
            return HasherError.InvalidEncoding;

        const rounds_log_str = str[4..][0..2];
        const rounds_log = fmt.parseInt(u6, rounds_log_str[0..], 10) catch
            return HasherError.InvalidEncoding;

        const salt_str = str[7..][0..salt_str_length];
        var salt: [salt_length]u8 = undefined;
        try crypt_format.Codec.decode(salt[0..], salt_str[0..]);

        const wanted_s = crypt_format.strHashInternal(password, salt, .{ .rounds_log = rounds_log });
        if (!mem.eql(u8, wanted_s[0..], str[0..])) return HasherError.PasswordVerificationFailed;
    }
};

/// Options for hashing a password.
pub const HashOptions = struct {
    allocator: ?mem.Allocator = null,
    params: Params,
    encoding: pwhash.Encoding,
};

/// Compute a hash of a password using 2^rounds_log rounds of the bcrypt key stretching function.
/// bcrypt is a computationally expensive and cache-hard function, explicitly designed to slow down exhaustive searches.
///
/// The function returns a string that includes all the parameters required for verification.
///
/// IMPORTANT: by design, bcrypt silently truncates passwords to 72 bytes.
/// If this is an issue for your application, hash the password first using a function such as SHA-512,
/// and then use the resulting hash as the password parameter for bcrypt.
pub fn strHash(
    password: []const u8,
    options: HashOptions,
    out: []u8,
) Error![]const u8 {
    switch (options.encoding) {
        .phc => return PhcFormatHasher.create(password, options.params, out),
        .crypt => return CryptFormatHasher.create(password, options.params, out),
    }
}

/// Options for hash verification.
pub const VerifyOptions = struct {
    allocator: ?mem.Allocator = null,
};

/// Verify that a previously computed hash is valid for a given password.
pub fn strVerify(
    str: []const u8,
    password: []const u8,
    _: VerifyOptions,
) Error!void {
    if (mem.startsWith(u8, str, crypt_format.prefix)) {
        return CryptFormatHasher.verify(str, password);
    } else {
        return PhcFormatHasher.verify(str, password);
    }
}

test "bcrypt codec" {
    var salt: [salt_length]u8 = undefined;
    crypto.random.bytes(&salt);
    var salt_str: [salt_str_length]u8 = undefined;
    crypt_format.Codec.encode(salt_str[0..], salt[0..]);
    var salt2: [salt_length]u8 = undefined;
    try crypt_format.Codec.decode(salt2[0..], salt_str[0..]);
    try testing.expectEqualSlices(u8, salt[0..], salt2[0..]);
}

test "bcrypt crypt format" {
    const hash_options = HashOptions{
        .params = .{ .rounds_log = 5 },
        .encoding = .crypt,
    };
    const verify_options = VerifyOptions{};

    var buf: [hash_length]u8 = undefined;
    const s = try strHash("password", hash_options, &buf);

    try testing.expect(mem.startsWith(u8, s, crypt_format.prefix));
    try strVerify(s, "password", verify_options);
    try testing.expectError(
        error.PasswordVerificationFailed,
        strVerify(s, "invalid password", verify_options),
    );

    var long_buf: [hash_length]u8 = undefined;
    const long_s = try strHash("password" ** 100, hash_options, &long_buf);

    try testing.expect(mem.startsWith(u8, long_s, crypt_format.prefix));
    try strVerify(long_s, "password" ** 100, verify_options);
    try strVerify(long_s, "password" ** 101, verify_options);

    try strVerify(
        "$2b$08$WUQKyBCaKpziCwUXHiMVvu40dYVjkTxtWJlftl0PpjY2BxWSvFIEe",
        "The devil himself",
        verify_options,
    );
}

test "bcrypt phc format" {
    const hash_options = HashOptions{
        .params = .{ .rounds_log = 5 },
        .encoding = .phc,
    };
    const verify_options = VerifyOptions{};
    const prefix = "$bcrypt$";

    var buf: [hash_length * 2]u8 = undefined;
    const s = try strHash("password", hash_options, &buf);

    try testing.expect(mem.startsWith(u8, s, prefix));
    try strVerify(s, "password", verify_options);
    try testing.expectError(
        error.PasswordVerificationFailed,
        strVerify(s, "invalid password", verify_options),
    );

    var long_buf: [hash_length * 2]u8 = undefined;
    const long_s = try strHash("password" ** 100, hash_options, &long_buf);

    try testing.expect(mem.startsWith(u8, long_s, prefix));
    try strVerify(long_s, "password" ** 100, verify_options);
    try strVerify(long_s, "password" ** 101, verify_options);

    try strVerify(
        "$bcrypt$r=5$2NopntlgE2lX3cTwr4qz8A$r3T7iKYQNnY4hAhGjk9RmuyvgrYJZwc",
        "The devil himself",
        verify_options,
    );
}
