Blowfish.java

package com.thealgorithms.ciphers;

/*
 * Java program for Blowfish Algorithm
 * Wikipedia: https://en.wikipedia.org/wiki/Blowfish_(cipher)
 *
 * Author: Akshay Dubey (https://github.com/itsAkshayDubey)
 *
 * */

public class Blowfish {

    // Initializing substitution boxes
    String[][] sBox = {
        {
            "d1310ba6",
            "98dfb5ac",
            "2ffd72db",
            "d01adfb7",
            "b8e1afed",
            "6a267e96",
            "ba7c9045",
            "f12c7f99",
            "24a19947",
            "b3916cf7",
            "0801f2e2",
            "858efc16",
            "636920d8",
            "71574e69",
            "a458fea3",
            "f4933d7e",
            "0d95748f",
            "728eb658",
            "718bcd58",
            "82154aee",
            "7b54a41d",
            "c25a59b5",
            "9c30d539",
            "2af26013",
            "c5d1b023",
            "286085f0",
            "ca417918",
            "b8db38ef",
            "8e79dcb0",
            "603a180e",
            "6c9e0e8b",
            "b01e8a3e",
            "d71577c1",
            "bd314b27",
            "78af2fda",
            "55605c60",
            "e65525f3",
            "aa55ab94",
            "57489862",
            "63e81440",
            "55ca396a",
            "2aab10b6",
            "b4cc5c34",
            "1141e8ce",
            "a15486af",
            "7c72e993",
            "b3ee1411",
            "636fbc2a",
            "2ba9c55d",
            "741831f6",
            "ce5c3e16",
            "9b87931e",
            "afd6ba33",
            "6c24cf5c",
            "7a325381",
            "28958677",
            "3b8f4898",
            "6b4bb9af",
            "c4bfe81b",
            "66282193",
            "61d809cc",
            "fb21a991",
            "487cac60",
            "5dec8032",
            "ef845d5d",
            "e98575b1",
            "dc262302",
            "eb651b88",
            "23893e81",
            "d396acc5",
            "0f6d6ff3",
            "83f44239",
            "2e0b4482",
            "a4842004",
            "69c8f04a",
            "9e1f9b5e",
            "21c66842",
            "f6e96c9a",
            "670c9c61",
            "abd388f0",
            "6a51a0d2",
            "d8542f68",
            "960fa728",
            "ab5133a3",
            "6eef0b6c",
            "137a3be4",
            "ba3bf050",
            "7efb2a98",
            "a1f1651d",
            "39af0176",
            "66ca593e",
            "82430e88",
            "8cee8619",
            "456f9fb4",
            "7d84a5c3",
            "3b8b5ebe",
            "e06f75d8",
            "85c12073",
            "401a449f",
            "56c16aa6",
            "4ed3aa62",
            "363f7706",
            "1bfedf72",
            "429b023d",
            "37d0d724",
            "d00a1248",
            "db0fead3",
            "49f1c09b",
            "075372c9",
            "80991b7b",
            "25d479d8",
            "f6e8def7",
            "e3fe501a",
            "b6794c3b",
            "976ce0bd",
            "04c006ba",
            "c1a94fb6",
            "409f60c4",
            "5e5c9ec2",
            "196a2463",
            "68fb6faf",
            "3e6c53b5",
            "1339b2eb",
            "3b52ec6f",
            "6dfc511f",
            "9b30952c",
            "cc814544",
            "af5ebd09",
            "bee3d004",
            "de334afd",
            "660f2807",
            "192e4bb3",
            "c0cba857",
            "45c8740f",
            "d20b5f39",
            "b9d3fbdb",
            "5579c0bd",
            "1a60320a",
            "d6a100c6",
            "402c7279",
            "679f25fe",
            "fb1fa3cc",
            "8ea5e9f8",
            "db3222f8",
            "3c7516df",
            "fd616b15",
            "2f501ec8",
            "ad0552ab",
            "323db5fa",
            "fd238760",
            "53317b48",
            "3e00df82",
            "9e5c57bb",
            "ca6f8ca0",
            "1a87562e",
            "df1769db",
            "d542a8f6",
            "287effc3",
            "ac6732c6",
            "8c4f5573",
            "695b27b0",
            "bbca58c8",
            "e1ffa35d",
            "b8f011a0",
            "10fa3d98",
            "fd2183b8",
            "4afcb56c",
            "2dd1d35b",
            "9a53e479",
            "b6f84565",
            "d28e49bc",
            "4bfb9790",
            "e1ddf2da",
            "a4cb7e33",
            "62fb1341",
            "cee4c6e8",
            "ef20cada",
            "36774c01",
            "d07e9efe",
            "2bf11fb4",
            "95dbda4d",
            "ae909198",
            "eaad8e71",
            "6b93d5a0",
            "d08ed1d0",
            "afc725e0",
            "8e3c5b2f",
            "8e7594b7",
            "8ff6e2fb",
            "f2122b64",
            "8888b812",
            "900df01c",
            "4fad5ea0",
            "688fc31c",
            "d1cff191",
            "b3a8c1ad",
            "2f2f2218",
            "be0e1777",
            "ea752dfe",
            "8b021fa1",
            "e5a0cc0f",
            "b56f74e8",
            "18acf3d6",
            "ce89e299",
            "b4a84fe0",
            "fd13e0b7",
            "7cc43b81",
            "d2ada8d9",
            "165fa266",
            "80957705",
            "93cc7314",
            "211a1477",
            "e6ad2065",
            "77b5fa86",
            "c75442f5",
            "fb9d35cf",
            "ebcdaf0c",
            "7b3e89a0",
            "d6411bd3",
            "ae1e7e49",
            "00250e2d",
            "2071b35e",
            "226800bb",
            "57b8e0af",
            "2464369b",
            "f009b91e",
            "5563911d",
            "59dfa6aa",
            "78c14389",
            "d95a537f",
            "207d5ba2",
            "02e5b9c5",
            "83260376",
            "6295cfa9",
            "11c81968",
            "4e734a41",
            "b3472dca",
            "7b14a94a",
            "1b510052",
            "9a532915",
            "d60f573f",
            "bc9bc6e4",
            "2b60a476",
            "81e67400",
            "08ba6fb5",
            "571be91f",
            "f296ec6b",
            "2a0dd915",
            "b6636521",
            "e7b9f9b6",
            "ff34052e",
            "c5855664",
            "53b02d5d",
            "a99f8fa1",
            "08ba4799",
            "6e85076a",
        },
        {
            "4b7a70e9",
            "b5b32944",
            "db75092e",
            "c4192623",
            "ad6ea6b0",
            "49a7df7d",
            "9cee60b8",
            "8fedb266",
            "ecaa8c71",
            "699a17ff",
            "5664526c",
            "c2b19ee1",
            "193602a5",
            "75094c29",
            "a0591340",
            "e4183a3e",
            "3f54989a",
            "5b429d65",
            "6b8fe4d6",
            "99f73fd6",
            "a1d29c07",
            "efe830f5",
            "4d2d38e6",
            "f0255dc1",
            "4cdd2086",
            "8470eb26",
            "6382e9c6",
            "021ecc5e",
            "09686b3f",
            "3ebaefc9",
            "3c971814",
            "6b6a70a1",
            "687f3584",
            "52a0e286",
            "b79c5305",
            "aa500737",
            "3e07841c",
            "7fdeae5c",
            "8e7d44ec",
            "5716f2b8",
            "b03ada37",
            "f0500c0d",
            "f01c1f04",
            "0200b3ff",
            "ae0cf51a",
            "3cb574b2",
            "25837a58",
            "dc0921bd",
            "d19113f9",
            "7ca92ff6",
            "94324773",
            "22f54701",
            "3ae5e581",
            "37c2dadc",
            "c8b57634",
            "9af3dda7",
            "a9446146",
            "0fd0030e",
            "ecc8c73e",
            "a4751e41",
            "e238cd99",
            "3bea0e2f",
            "3280bba1",
            "183eb331",
            "4e548b38",
            "4f6db908",
            "6f420d03",
            "f60a04bf",
            "2cb81290",
            "24977c79",
            "5679b072",
            "bcaf89af",
            "de9a771f",
            "d9930810",
            "b38bae12",
            "dccf3f2e",
            "5512721f",
            "2e6b7124",
            "501adde6",
            "9f84cd87",
            "7a584718",
            "7408da17",
            "bc9f9abc",
            "e94b7d8c",
            "ec7aec3a",
            "db851dfa",
            "63094366",
            "c464c3d2",
            "ef1c1847",
            "3215d908",
            "dd433b37",
            "24c2ba16",
            "12a14d43",
            "2a65c451",
            "50940002",
            "133ae4dd",
            "71dff89e",
            "10314e55",
            "81ac77d6",
            "5f11199b",
            "043556f1",
            "d7a3c76b",
            "3c11183b",
            "5924a509",
            "f28fe6ed",
            "97f1fbfa",
            "9ebabf2c",
            "1e153c6e",
            "86e34570",
            "eae96fb1",
            "860e5e0a",
            "5a3e2ab3",
            "771fe71c",
            "4e3d06fa",
            "2965dcb9",
            "99e71d0f",
            "803e89d6",
            "5266c825",
            "2e4cc978",
            "9c10b36a",
            "c6150eba",
            "94e2ea78",
            "a5fc3c53",
            "1e0a2df4",
            "f2f74ea7",
            "361d2b3d",
            "1939260f",
            "19c27960",
            "5223a708",
            "f71312b6",
            "ebadfe6e",
            "eac31f66",
            "e3bc4595",
            "a67bc883",
            "b17f37d1",
            "018cff28",
            "c332ddef",
            "be6c5aa5",
            "65582185",
            "68ab9802",
            "eecea50f",
            "db2f953b",
            "2aef7dad",
            "5b6e2f84",
            "1521b628",
            "29076170",
            "ecdd4775",
            "619f1510",
            "13cca830",
            "eb61bd96",
            "0334fe1e",
            "aa0363cf",
            "b5735c90",
            "4c70a239",
            "d59e9e0b",
            "cbaade14",
            "eecc86bc",
            "60622ca7",
            "9cab5cab",
            "b2f3846e",
            "648b1eaf",
            "19bdf0ca",
            "a02369b9",
            "655abb50",
            "40685a32",
            "3c2ab4b3",
            "319ee9d5",
            "c021b8f7",
            "9b540b19",
            "875fa099",
            "95f7997e",
            "623d7da8",
            "f837889a",
            "97e32d77",
            "11ed935f",
            "16681281",
            "0e358829",
            "c7e61fd6",
            "96dedfa1",
            "7858ba99",
            "57f584a5",
            "1b227263",
            "9b83c3ff",
            "1ac24696",
            "cdb30aeb",
            "532e3054",
            "8fd948e4",
            "6dbc3128",
            "58ebf2ef",
            "34c6ffea",
            "fe28ed61",
            "ee7c3c73",
            "5d4a14d9",
            "e864b7e3",
            "42105d14",
            "203e13e0",
            "45eee2b6",
            "a3aaabea",
            "db6c4f15",
            "facb4fd0",
            "c742f442",
            "ef6abbb5",
            "654f3b1d",
            "41cd2105",
            "d81e799e",
            "86854dc7",
            "e44b476a",
            "3d816250",
            "cf62a1f2",
            "5b8d2646",
            "fc8883a0",
            "c1c7b6a3",
            "7f1524c3",
            "69cb7492",
            "47848a0b",
            "5692b285",
            "095bbf00",
            "ad19489d",
            "1462b174",
            "23820e00",
            "58428d2a",
            "0c55f5ea",
            "1dadf43e",
            "233f7061",
            "3372f092",
            "8d937e41",
            "d65fecf1",
            "6c223bdb",
            "7cde3759",
            "cbee7460",
            "4085f2a7",
            "ce77326e",
            "a6078084",
            "19f8509e",
            "e8efd855",
            "61d99735",
            "a969a7aa",
            "c50c06c2",
            "5a04abfc",
            "800bcadc",
            "9e447a2e",
            "c3453484",
            "fdd56705",
            "0e1e9ec9",
            "db73dbd3",
            "105588cd",
            "675fda79",
            "e3674340",
            "c5c43465",
            "713e38d8",
            "3d28f89e",
            "f16dff20",
            "153e21e7",
            "8fb03d4a",
            "e6e39f2b",
            "db83adf7",
        },
        {
            "e93d5a68",
            "948140f7",
            "f64c261c",
            "94692934",
            "411520f7",
            "7602d4f7",
            "bcf46b2e",
            "d4a20068",
            "d4082471",
            "3320f46a",
            "43b7d4b7",
            "500061af",
            "1e39f62e",
            "97244546",
            "14214f74",
            "bf8b8840",
            "4d95fc1d",
            "96b591af",
            "70f4ddd3",
            "66a02f45",
            "bfbc09ec",
            "03bd9785",
            "7fac6dd0",
            "31cb8504",
            "96eb27b3",
            "55fd3941",
            "da2547e6",
            "abca0a9a",
            "28507825",
            "530429f4",
            "0a2c86da",
            "e9b66dfb",
            "68dc1462",
            "d7486900",
            "680ec0a4",
            "27a18dee",
            "4f3ffea2",
            "e887ad8c",
            "b58ce006",
            "7af4d6b6",
            "aace1e7c",
            "d3375fec",
            "ce78a399",
            "406b2a42",
            "20fe9e35",
            "d9f385b9",
            "ee39d7ab",
            "3b124e8b",
            "1dc9faf7",
            "4b6d1856",
            "26a36631",
            "eae397b2",
            "3a6efa74",
            "dd5b4332",
            "6841e7f7",
            "ca7820fb",
            "fb0af54e",
            "d8feb397",
            "454056ac",
            "ba489527",
            "55533a3a",
            "20838d87",
            "fe6ba9b7",
            "d096954b",
            "55a867bc",
            "a1159a58",
            "cca92963",
            "99e1db33",
            "a62a4a56",
            "3f3125f9",
            "5ef47e1c",
            "9029317c",
            "fdf8e802",
            "04272f70",
            "80bb155c",
            "05282ce3",
            "95c11548",
            "e4c66d22",
            "48c1133f",
            "c70f86dc",
            "07f9c9ee",
            "41041f0f",
            "404779a4",
            "5d886e17",
            "325f51eb",
            "d59bc0d1",
            "f2bcc18f",
            "41113564",
            "257b7834",
            "602a9c60",
            "dff8e8a3",
            "1f636c1b",
            "0e12b4c2",
            "02e1329e",
            "af664fd1",
            "cad18115",
            "6b2395e0",
            "333e92e1",
            "3b240b62",
            "eebeb922",
            "85b2a20e",
            "e6ba0d99",
            "de720c8c",
            "2da2f728",
            "d0127845",
            "95b794fd",
            "647d0862",
            "e7ccf5f0",
            "5449a36f",
            "877d48fa",
            "c39dfd27",
            "f33e8d1e",
            "0a476341",
            "992eff74",
            "3a6f6eab",
            "f4f8fd37",
            "a812dc60",
            "a1ebddf8",
            "991be14c",
            "db6e6b0d",
            "c67b5510",
            "6d672c37",
            "2765d43b",
            "dcd0e804",
            "f1290dc7",
            "cc00ffa3",
            "b5390f92",
            "690fed0b",
            "667b9ffb",
            "cedb7d9c",
            "a091cf0b",
            "d9155ea3",
            "bb132f88",
            "515bad24",
            "7b9479bf",
            "763bd6eb",
            "37392eb3",
            "cc115979",
            "8026e297",
            "f42e312d",
            "6842ada7",
            "c66a2b3b",
            "12754ccc",
            "782ef11c",
            "6a124237",
            "b79251e7",
            "06a1bbe6",
            "4bfb6350",
            "1a6b1018",
            "11caedfa",
            "3d25bdd8",
            "e2e1c3c9",
            "44421659",
            "0a121386",
            "d90cec6e",
            "d5abea2a",
            "64af674e",
            "da86a85f",
            "bebfe988",
            "64e4c3fe",
            "9dbc8057",
            "f0f7c086",
            "60787bf8",
            "6003604d",
            "d1fd8346",
            "f6381fb0",
            "7745ae04",
            "d736fccc",
            "83426b33",
            "f01eab71",
            "b0804187",
            "3c005e5f",
            "77a057be",
            "bde8ae24",
            "55464299",
            "bf582e61",
            "4e58f48f",
            "f2ddfda2",
            "f474ef38",
            "8789bdc2",
            "5366f9c3",
            "c8b38e74",
            "b475f255",
            "46fcd9b9",
            "7aeb2661",
            "8b1ddf84",
            "846a0e79",
            "915f95e2",
            "466e598e",
            "20b45770",
            "8cd55591",
            "c902de4c",
            "b90bace1",
            "bb8205d0",
            "11a86248",
            "7574a99e",
            "b77f19b6",
            "e0a9dc09",
            "662d09a1",
            "c4324633",
            "e85a1f02",
            "09f0be8c",
            "4a99a025",
            "1d6efe10",
            "1ab93d1d",
            "0ba5a4df",
            "a186f20f",
            "2868f169",
            "dcb7da83",
            "573906fe",
            "a1e2ce9b",
            "4fcd7f52",
            "50115e01",
            "a70683fa",
            "a002b5c4",
            "0de6d027",
            "9af88c27",
            "773f8641",
            "c3604c06",
            "61a806b5",
            "f0177a28",
            "c0f586e0",
            "006058aa",
            "30dc7d62",
            "11e69ed7",
            "2338ea63",
            "53c2dd94",
            "c2c21634",
            "bbcbee56",
            "90bcb6de",
            "ebfc7da1",
            "ce591d76",
            "6f05e409",
            "4b7c0188",
            "39720a3d",
            "7c927c24",
            "86e3725f",
            "724d9db9",
            "1ac15bb4",
            "d39eb8fc",
            "ed545578",
            "08fca5b5",
            "d83d7cd3",
            "4dad0fc4",
            "1e50ef5e",
            "b161e6f8",
            "a28514d9",
            "6c51133c",
            "6fd5c7e7",
            "56e14ec4",
            "362abfce",
            "ddc6c837",
            "d79a3234",
            "92638212",
            "670efa8e",
            "406000e0",
        },
        {
            "3a39ce37",
            "d3faf5cf",
            "abc27737",
            "5ac52d1b",
            "5cb0679e",
            "4fa33742",
            "d3822740",
            "99bc9bbe",
            "d5118e9d",
            "bf0f7315",
            "d62d1c7e",
            "c700c47b",
            "b78c1b6b",
            "21a19045",
            "b26eb1be",
            "6a366eb4",
            "5748ab2f",
            "bc946e79",
            "c6a376d2",
            "6549c2c8",
            "530ff8ee",
            "468dde7d",
            "d5730a1d",
            "4cd04dc6",
            "2939bbdb",
            "a9ba4650",
            "ac9526e8",
            "be5ee304",
            "a1fad5f0",
            "6a2d519a",
            "63ef8ce2",
            "9a86ee22",
            "c089c2b8",
            "43242ef6",
            "a51e03aa",
            "9cf2d0a4",
            "83c061ba",
            "9be96a4d",
            "8fe51550",
            "ba645bd6",
            "2826a2f9",
            "a73a3ae1",
            "4ba99586",
            "ef5562e9",
            "c72fefd3",
            "f752f7da",
            "3f046f69",
            "77fa0a59",
            "80e4a915",
            "87b08601",
            "9b09e6ad",
            "3b3ee593",
            "e990fd5a",
            "9e34d797",
            "2cf0b7d9",
            "022b8b51",
            "96d5ac3a",
            "017da67d",
            "d1cf3ed6",
            "7c7d2d28",
            "1f9f25cf",
            "adf2b89b",
            "5ad6b472",
            "5a88f54c",
            "e029ac71",
            "e019a5e6",
            "47b0acfd",
            "ed93fa9b",
            "e8d3c48d",
            "283b57cc",
            "f8d56629",
            "79132e28",
            "785f0191",
            "ed756055",
            "f7960e44",
            "e3d35e8c",
            "15056dd4",
            "88f46dba",
            "03a16125",
            "0564f0bd",
            "c3eb9e15",
            "3c9057a2",
            "97271aec",
            "a93a072a",
            "1b3f6d9b",
            "1e6321f5",
            "f59c66fb",
            "26dcf319",
            "7533d928",
            "b155fdf5",
            "03563482",
            "8aba3cbb",
            "28517711",
            "c20ad9f8",
            "abcc5167",
            "ccad925f",
            "4de81751",
            "3830dc8e",
            "379d5862",
            "9320f991",
            "ea7a90c2",
            "fb3e7bce",
            "5121ce64",
            "774fbe32",
            "a8b6e37e",
            "c3293d46",
            "48de5369",
            "6413e680",
            "a2ae0810",
            "dd6db224",
            "69852dfd",
            "09072166",
            "b39a460a",
            "6445c0dd",
            "586cdecf",
            "1c20c8ae",
            "5bbef7dd",
            "1b588d40",
            "ccd2017f",
            "6bb4e3bb",
            "dda26a7e",
            "3a59ff45",
            "3e350a44",
            "bcb4cdd5",
            "72eacea8",
            "fa6484bb",
            "8d6612ae",
            "bf3c6f47",
            "d29be463",
            "542f5d9e",
            "aec2771b",
            "f64e6370",
            "740e0d8d",
            "e75b1357",
            "f8721671",
            "af537d5d",
            "4040cb08",
            "4eb4e2cc",
            "34d2466a",
            "0115af84",
            "e1b00428",
            "95983a1d",
            "06b89fb4",
            "ce6ea048",
            "6f3f3b82",
            "3520ab82",
            "011a1d4b",
            "277227f8",
            "611560b1",
            "e7933fdc",
            "bb3a792b",
            "344525bd",
            "a08839e1",
            "51ce794b",
            "2f32c9b7",
            "a01fbac9",
            "e01cc87e",
            "bcc7d1f6",
            "cf0111c3",
            "a1e8aac7",
            "1a908749",
            "d44fbd9a",
            "d0dadecb",
            "d50ada38",
            "0339c32a",
            "c6913667",
            "8df9317c",
            "e0b12b4f",
            "f79e59b7",
            "43f5bb3a",
            "f2d519ff",
            "27d9459c",
            "bf97222c",
            "15e6fc2a",
            "0f91fc71",
            "9b941525",
            "fae59361",
            "ceb69ceb",
            "c2a86459",
            "12baa8d1",
            "b6c1075e",
            "e3056a0c",
            "10d25065",
            "cb03a442",
            "e0ec6e0e",
            "1698db3b",
            "4c98a0be",
            "3278e964",
            "9f1f9532",
            "e0d392df",
            "d3a0342b",
            "8971f21e",
            "1b0a7441",
            "4ba3348c",
            "c5be7120",
            "c37632d8",
            "df359f8d",
            "9b992f2e",
            "e60b6f47",
            "0fe3f11d",
            "e54cda54",
            "1edad891",
            "ce6279cf",
            "cd3e7e6f",
            "1618b166",
            "fd2c1d05",
            "848fd2c5",
            "f6fb2299",
            "f523f357",
            "a6327623",
            "93a83531",
            "56cccd02",
            "acf08162",
            "5a75ebb5",
            "6e163697",
            "88d273cc",
            "de966292",
            "81b949d0",
            "4c50901b",
            "71c65614",
            "e6c6c7bd",
            "327a140a",
            "45e1d006",
            "c3f27b9a",
            "c9aa53fd",
            "62a80f00",
            "bb25bfe2",
            "35bdd2f6",
            "71126905",
            "b2040222",
            "b6cbcf7c",
            "cd769c2b",
            "53113ec0",
            "1640e3d3",
            "38abbd60",
            "2547adf0",
            "ba38209c",
            "f746ce76",
            "77afa1c5",
            "20756060",
            "85cbfe4e",
            "8ae88dd8",
            "7aaaf9b0",
            "4cf9aa7e",
            "1948c25c",
            "02fb8a8c",
            "01c36ae4",
            "d6ebe1f9",
            "90d4f869",
            "a65cdea0",
            "3f09252d",
            "c208e69f",
            "b74e6132",
            "ce77e25b",
            "578fdfe3",
            "3ac372e6",
        },
    };

    // Initializing subkeys with digits of pi
    String[] subKeys = {
        "243f6a88",
        "85a308d3",
        "13198a2e",
        "03707344",
        "a4093822",
        "299f31d0",
        "082efa98",
        "ec4e6c89",
        "452821e6",
        "38d01377",
        "be5466cf",
        "34e90c6c",
        "c0ac29b7",
        "c97c50dd",
        "3f84d5b5",
        "b5470917",
        "9216d5d9",
        "8979fb1b",
    };

    // Initializing modVal to 2^32
    long modVal = 4294967296L;

    /**
     * This method returns binary representation of the hexadecimal number passed as parameter
     *
     * @param hex Number for which binary representation is required
     * @return String object which is a binary representation of the hex number passed as parameter
     */
    private String hexToBin(String hex) {
        String binary = "";
        long num;
        String binary4B;
        int n = hex.length();
        for (int i = 0; i < n; i++) {
            num = Long.parseUnsignedLong(hex.charAt(i) + "", 16);
            binary4B = Long.toBinaryString(num);

            binary4B = "0000" + binary4B;

            binary4B = binary4B.substring(binary4B.length() - 4);
            binary += binary4B;
        }
        return binary;
    }

    /**
     * This method returns hexadecimal representation of the binary number passed as parameter
     *
     * @param binary Number for which hexadecimal representation is required
     * @return String object which is a hexadecimal representation of the binary number passed as
     *     parameter
     */
    private String binToHex(String binary) {
        long num = Long.parseUnsignedLong(binary, 2);
        String hex = Long.toHexString(num);
        while (hex.length() < (binary.length() / 4)) hex = "0" + hex;

        return hex;
    }

    /**
     * This method returns a string obtained by XOR-ing two strings of same length passed a method
     * parameters
     *
     * @param String a and b are string objects which will be XORed and are to be of same length
     * @return String object obtained by XOR operation on String a and String b
     * */
    private String xor(String a, String b) {
        a = hexToBin(a);
        b = hexToBin(b);
        String ans = "";
        for (int i = 0; i < a.length(); i++) ans += (char) (((a.charAt(i) - '0') ^ (b.charAt(i) - '0')) + '0');
        ans = binToHex(ans);
        return ans;
    }

    /**
     * This method returns addition of two hexadecimal numbers passed as parameters and moded with
     * 2^32
     *
     * @param String a and b are hexadecimal numbers
     * @return String object which is a is addition that is then moded with 2^32 of hex numbers
     *     passed as parameters
     */
    private String addBin(String a, String b) {
        String ans = "";
        long n1 = Long.parseUnsignedLong(a, 16);
        long n2 = Long.parseUnsignedLong(b, 16);
        n1 = (n1 + n2) % modVal;
        ans = Long.toHexString(n1);
        ans = "00000000" + ans;
        return ans.substring(ans.length() - 8);
    }

    /*F-function splits the 32-bit input into four 8-bit quarters
         and uses the quarters as input to the S-boxes.
         The S-boxes accept 8-bit input and produce 32-bit output.
         The outputs are added modulo 232 and XORed to produce the final 32-bit output
        */
    private String f(String plainText) {
        String[] a = new String[4];
        String ans = "";
        for (int i = 0; i < 8; i += 2) {
            // column number for S-box is a 8-bit value
            long col = Long.parseUnsignedLong(hexToBin(plainText.substring(i, i + 2)), 2);
            a[i / 2] = sBox[i / 2][(int) col];
        }
        ans = addBin(a[0], a[1]);
        ans = xor(ans, a[2]);
        ans = addBin(ans, a[3]);
        return ans;
    }

    // generate subkeys
    private void keyGenerate(String key) {
        int j = 0;
        for (int i = 0; i < subKeys.length; i++) {
            // XOR-ing 32-bit parts of the key with initial subkeys
            subKeys[i] = xor(subKeys[i], key.substring(j, j + 8));

            j = (j + 8) % key.length();
        }
    }

    // round function
    private String round(int time, String plainText) {
        String left;
        String right;
        left = plainText.substring(0, 8);
        right = plainText.substring(8, 16);
        left = xor(left, subKeys[time]);

        // output from F function
        String fOut = f(left);

        right = xor(fOut, right);

        // swap left and right
        return right + left;
    }

    /**
     * This method returns cipher text for the plaintext passed as the first parameter generated
     * using the key passed as the second parameter
     *
     * @param String plainText is the text which is to be encrypted
     * @param String key is the key which is to be used for generating cipher text
     * @return String cipherText is the encrypted value
     */
    String encrypt(String plainText, String key) {
        // generating key
        keyGenerate(key);

        for (int i = 0; i < 16; i++) plainText = round(i, plainText);

        // postprocessing
        String right = plainText.substring(0, 8);
        String left = plainText.substring(8, 16);
        right = xor(right, subKeys[16]);
        left = xor(left, subKeys[17]);
        return left + right;
    }

    /**
     * This method returns plaintext for the ciphertext passed as the first parameter decoded
     * using the key passed as the second parameter
     *
     * @param String ciphertext is the text which is to be decrypted
     * @param String key is the key which is to be used for generating cipher text
     * @return String plainText is the decrypted text
     */
    String decrypt(String cipherText, String key) {
        // generating key
        keyGenerate(key);

        for (int i = 17; i > 1; i--) cipherText = round(i, cipherText);

        // postprocessing
        String right = cipherText.substring(0, 8);
        String left = cipherText.substring(8, 16);
        right = xor(right, subKeys[1]);
        left = xor(left, subKeys[0]);
        return left + right;
    }
}