    const std = @import("std");
    const base64 = std.base64;
    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 Sha512 = crypto.hash.sha2.Sha512;
    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;

    pub 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 pbkdf_prf = struct {
        const Self = @This();
        pub const mac_length = 32;

        hasher: Sha512,
        sha2pass: [Sha512.digest_length]u8,

        pub fn create(out: *[mac_length]u8, msg: []const u8, key: []const u8) void {
            var ctx = Self.init(key);
            ctx.update(msg);
            ctx.final(out);
        }

        pub fn init(key: []const u8) Self {
            var self: Self = undefined;
            self.hasher = Sha512.init(.{});
            Sha512.hash(key, &self.sha2pass, .{});
            return self;
        }

        pub fn update(self: *Self, msg: []const u8) void {
            self.hasher.update(msg);
        }

        pub fn final(self: *Self, out: *[mac_length]u8) void {
            var sha2salt: [Sha512.digest_length]u8 = undefined;
            self.hasher.final(&sha2salt);
            out.* = hash(self.sha2pass, sha2salt);
        }

        /// Matches OpenBSD function
        /// https://github.com/openbsd/src/blob/6df1256b7792691e66c2ed9d86a8c103069f9e34/lib/libutil/bcrypt_pbkdf.c#L98
        fn hash(sha2pass: [Sha512.digest_length]u8, sha2salt: [Sha512.digest_length]u8) [32]u8 {
            var cdata: [8]u32 = undefined;
            {
                const ciphertext = "OxychromaticBlowfishSwatDynamite";
                var j: usize = 0;
                for (cdata) |*v| {
                    v.* = State.toWord(ciphertext, &j);
                }
            }

            var state = State{};

            { // key expansion

                state.expand(&sha2salt, &sha2pass);
                var i: usize = 0;
                while (i < 64) : (i += 1) {
                    state.expand0(&sha2salt);
                    state.expand0(&sha2pass);
                }
            }

            { // encryption

                var i: usize = 0;
                while (i < 64) : (i += 1) {
                    state.encrypt(&cdata);
                }
            }

            // copy out

            var out: [32]u8 = undefined;
            for (cdata) |v, i| {
                std.mem.writeIntLittle(u32, out[4 * i ..][0..4], v);
            }

            // zap

            crypto.utils.secureZero(u32, &cdata);
            crypto.utils.secureZero(State, @as(*[1]State, &state));

            return out;
        }
    };

    /// bcrypt PBKDF2 implementation with variations to match OpenBSD
    /// https://github.com/openbsd/src/blob/6df1256b7792691e66c2ed9d86a8c103069f9e34/lib/libutil/bcrypt_pbkdf.c#L98
    ///
    /// This particular variant is used in e.g. SSH
    pub fn pbkdf(pass: []const u8, salt: []const u8, key: []u8, rounds: u32) !void {
        try crypto.pwhash.pbkdf2(key, pass, salt, rounds, pbkdf_prf);
    }

    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 bcrypt_alphabet = "./ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789".*;
        const Codec = struct { Encoder: base64.Base64Encoder, Decoder: base64.Base64Decoder }{
            .Encoder = base64.Base64Encoder.init(bcrypt_alphabet, null),
            .Decoder = base64.Base64Decoder.init(bcrypt_alphabet, null),
        };

        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.Encoder.encode(salt_str[0..], salt[0..]);

            var ct_str: [ct_str_length]u8 = undefined;
            _ = Codec.Encoder.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;
            crypt_format.Codec.Decoder.decode(salt[0..], salt_str[0..]) catch return HasherError.InvalidEncoding;

            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.Encoder.encode(salt_str[0..], salt[0..]);
        var salt2: [salt_length]u8 = undefined;
        try crypt_format.Codec.Decoder.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,
        );
    }