Blowfish Algorithm with Examples

Last Updated : 21 May, 2025

Blowfish is an encryption technique designed by Bruce Schneier in 1993 as an alternative to the DES Encryption Technique. It is significantly faster than DES and provides a good encryption rate with no effective cryptanalysis technique found to date. It is one of the first secure block ciphers not subject to any patents and hence freely available for anyone to use. It is a symmetric block cipher algorithm.

blockSize: 64-bits
keySize: 32-bits to 448-bits variable size
Number of subkeys: 18 [P-array]
Number of rounds: 16
number of substitution boxes: 4 [each having 512 entries of 32 bits each]

Blowfish Encryption Algorithm

The entire encryption process can be elaborated as:

Lets see each step one by one:

Step 1: Generation of subkeys

18 subkeys{P[0]...P[17]} are needed in both encryption as well as decryption process and the same subkeys are used for both the processes.
These 18 subkeys are stored in a P-array with each array element being a 32-bit entry.
It is initialized with the digits of pi(?).
The hexadecimal representation of each of the subkeys is given by:

P[0] = "243f6a88"
P[1] = "85a308d3"
.
.
.
P[17] = "8979fb1b"

Now each of the subkey is changed with respect to the input key as:

P[0] = P[0] xor 1st 32-bits of input key
P[1] = P[1] xor 2nd 32-bits of input key
.
.
.
P[i] = P[i] xor (i+1)th 32-bits of input key
(roll over to 1st 32-bits depending on the key length)
.
.
.
P[17] = P[17] xor 18th 32-bits of input key
(roll over to 1st 32-bits depending on key length)

The resultant P-array holds 18 subkeys that is used during the entire encryption process

Step 2: Initialize Substitution Boxes

After expanding the P-array, The S-boxes are initialized with digits of pi.
4 Substitution boxes(S-boxes) are needed{S[0]...S[4]} in both encryption aswell as decryption process with each S-box having 256 entries{S[i][0]...S[i][255], 0&lei&le4} where each entry is 32-bit.
It is initialized with the digits of Љ ( pi ) after initializing the P-array.

Step 3: Encryption

The encryption function consists of two parts:
a. Rounds: The encryption consists of 16 rounds with each round(Ri) taking inputs the plainText(P.T.) from previous round and corresponding subkey(Pi). The description of each round is as follows:

The description of the function " F " is as follows:

Here, the function "add" is addition modulo 2^32.

b. Post-processing: The output after the 16 rounds is processed as follows:

blowfish

Below is a Java Program to demonstrate Blowfish encryption:

Java

import java.util.*; public class Encryption {  // S-boxes (truncated for brevity; normally 4 boxes each with 256 entries)  // For demonstration, using your given partial S-boxes:  String[][] S = {  { "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" }  // Normally there are 4 S-boxes each with 256 entries. For simplicity, only two here.  };  // P-array initial subkeys (18 entries)  String[] P = { "243f6a88", "85a308d3", "13198a2e", "03707344",  "a4093822", "299f31d0", "082efa98", "ec4e6c89",  "452821e6", "38d01377", "be5466cf", "34e90c6c",  "c0ac29b7", "c97c50dd", "3f84d5b5", "b5470917",  "9216d5d9", "8979fb1b" };  long modVal = 1L << 32; // 2^32  // Convert hex string to binary string  private String hexToBin(String hex) {  StringBuilder binary = new StringBuilder();  for (char c : hex.toCharArray()) {  int val = Integer.parseInt(String.valueOf(c), 16);  String bin4 = String.format("%4s", Integer.toBinaryString(val)).replace(' ', '0');  binary.append(bin4);  }  return binary.toString();  }  // Convert binary string to hex string  private String binToHex(String bin) {  long num = Long.parseUnsignedLong(bin, 2);  String hex = Long.toHexString(num);  while (hex.length() < bin.length() / 4) {  hex = "0" + hex;  }  return hex;  }  // XOR of two hex strings of same length  private String xor(String a, String b) {  String binA = hexToBin(a);  String binB = hexToBin(b);  StringBuilder res = new StringBuilder();  for (int i = 0; i < binA.length(); i++) {  res.append((binA.charAt(i) - '0') ^ (binB.charAt(i) - '0'));  }  return binToHex(res.toString());  }  // Addition modulo 2^32 of two hex strings  private String addMod32(String a, String b) {  long n1 = Long.parseUnsignedLong(a, 16);  long n2 = Long.parseUnsignedLong(b, 16);  long sum = (n1 + n2) % modVal;  String res = Long.toHexString(sum);  while (res.length() < 8) {  res = "0" + res;  }  return res;  }  // The F function of Blowfish  private String f(String x) {  // x is 8 hex chars (32 bits)  String[] parts = new String[4];  for (int i = 0; i < 4; i++) {  int index = Integer.parseInt(x.substring(i * 2, i * 2 + 2), 16);  parts[i] = S[i % S.length][index];  }  String res = addMod32(parts[0], parts[1]);  res = xor(res, parts[2]);  res = addMod32(res, parts[3]);  return res;  }  // Generate subkeys with key mixing  private void keyGenerate(String key) {  if (key.length() < 16) {  throw new IllegalArgumentException("Key must be at least 16 hex chars (64 bits)");  }  int j = 0;  for (int i = 0; i < P.length; i++) {  P[i] = xor(P[i], key.substring(j, j + 8));  j = (j + 8) % key.length();  }  }  // One round of Blowfish  private String round(int round, String data) {  String left = data.substring(0, 8);  String right = data.substring(8, 16);  left = xor(left, P[round]);  String fOut = f(left);  right = xor(right, fOut);  // Swap halves for next round  return right + left;  }  // Encrypt 64-bit block  private String encryptBlock(String block) {  for (int i = 0; i < 16; i++) {  block = round(i, block);  }  // Undo last swap  String left = block.substring(8, 16);  String right = block.substring(0, 8);  left = xor(left, P[16]);  right = xor(right, P[17]);  return left + right;  }  // Expand P-array and S-boxes with the key  private void expandKey() {  String block = "0000000000000000";  for (int i = 0; i < P.length; i += 2) {  block = encryptBlock(block);  P[i] = block.substring(0, 8);  if (i + 1 < P.length) P[i + 1] = block.substring(8, 16);  }  for (int s = 0; s < S.length; s++) {  for (int i = 0; i < S[s].length; i += 2) {  block = encryptBlock(block);  S[s][i] = block.substring(0, 8);  if (i + 1 < S[s].length) S[s][i + 1] = block.substring(8, 16);  }  }  }  // Main encryption function  private String encrypt(String plainText) {  if (plainText.length() != 16) {  throw new IllegalArgumentException("Plaintext must be 16 hex chars (64 bits)");  }  return encryptBlock(plainText);  }  public Encryption() {  String plainText = "123456abcd132536";  String key = "aabb09182736ccdd";  keyGenerate(key);  expandKey();  System.out.println("-----Encryption-----");  String cipherText = encrypt(plainText);  System.out.println("Cipher Text: " + cipherText);  }  public static void main(String[] args) {  new Encryption();  } }

Output:

Description

The decryption process is similar to that of encryption and the subkeys are used in reverse{P[17] - P[0]}. The entire decryption process can be elaborated as:

Lets see each step one by one:

Step 1: Generation of subkeys

18 subkeys{P[0]...P[17]} are needed in decryption process.
These 18 subkeys are stored in a P-array with each array element being a 32-bit entry.
It is initialized with the digits of pi(?).
The hexadecimal representation of each of the subkeys is given by:

P[0] = "243f6a88"
P[1] = "85a308d3"
.
.
.
P[17] = "8979fb1b"

Note: See encryption for the initial values of P-array.

Now each of the subkeys is changed with respect to the input key as:

P[0] = P[0] xor 1st 32-bits of input key
P[1] = P[1] xor 2nd 32-bits of input key
.
.
.
P[i] = P[i] xor (i+1)th 32-bits of input key
(roll over to 1st 32-bits depending on the key length)
.
.
.
P[17] = P[17] xor 18th 32-bits of input key
(roll over to 1st 32-bits depending on key length)

The resultant P-array holds 18 subkeys that is used during the entire encryption process

Step 2: Initialize Substitution Boxes

4 Substitution boxes(S-boxes) are needed{S[0]...S[4]} in both encryption aswell as decryption process with each S-box having 256 entries{S[i][0]...S[i][255], 0&lei&le4} where each entry is 32-bit.
It is initialized with the digits of pi(?) after initializing the P-array.

Step 3: Decryption

The Decryption function also consists of two parts:
1. Rounds: The decryption also consists of 16 rounds with each round(Ri)(as explained above) taking inputs the cipherText(C.T.) from previous round and corresponding subkey(P[17-i])(i.e for decryption the subkeys are used in reverse).
2. Post-processing: The output after the 16 rounds is processed as follows:

Below is a Java program to demonstrate decryption.

Java

public class BlowfishDemo {  private static final String[][] S = {  {  "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"  },  // S-box 2 (256 entries)...  {  "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"  },  // S-box 3 (256 entries)...  {  // Add all 256 entries from Blowfish spec here  "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",  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"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"  },  // S-box 4 (256 entries)...  {  // Fill with all 256 entries from Blowfish spec  "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"  }  };  // P-array initialization (18 entries)  private static final String[] P = {  "243f6a88", "85a308d3", "13198a2e", "03707344",  "a4093822", "299f31d0", "082efa98", "ec4e6c89",  "452821e6", "38d01377", "be5466cf", "34e90c6c",  "c0ac29b7", "c97c50dd", "3f84d5b5", "b5470917",  "9216d5d9", "8979fb1b"  };  // Instance copies of S and P to modify  private String[][] sBoxes = new String[4][256];  private String[] pArray = new String[18];  private long modVal = 1L << 32; // 2^32  public BlowfishDemo() {  // Deep copy arrays to instance variables  for (int i = 0; i < 4; i++) {  System.arraycopy(S[i], 0, sBoxes[i], 0, 256);  }  System.arraycopy(P, 0, pArray, 0, 18);  }  private String hexToBin(String hex) {  StringBuilder binary = new StringBuilder();  for (char ch : hex.toCharArray()) {  int val = Integer.parseInt(String.valueOf(ch), 16);  String binStr = Integer.toBinaryString(val);  binary.append("0000".substring(binStr.length())).append(binStr);  }  return binary.toString();  }  private String binToHex(String bin) {  StringBuilder hex = new StringBuilder();  for (int i = 0; i < bin.length(); i += 4) {  String nibble = bin.substring(i, i + 4);  hex.append(Integer.toHexString(Integer.parseInt(nibble, 2)));  }  return hex.toString();  }  private String xor(String a, String b) {  StringBuilder result = new StringBuilder();  String binA = hexToBin(a);  String binB = hexToBin(b);  for (int i = 0; i < binA.length(); i++) {  result.append(binA.charAt(i) == binB.charAt(i) ? '0' : '1');  }  return binToHex(result.toString());  }  private String addHexMod32(String a, String b) {  long valA = Long.parseUnsignedLong(a, 16);  long valB = Long.parseUnsignedLong(b, 16);  long sum = (valA + valB) % modVal;  String hexSum = Long.toHexString(sum);  while (hexSum.length() < 8) {  hexSum = "0" + hexSum;  }  return hexSum;  }  private String f(String x) {  // x is 8 hex chars = 32 bits  // Split x into four 8-bit parts (2 hex chars each)  String a = sBoxes[0][Integer.parseUnsignedInt(x.substring(0, 2), 16)];  String b = sBoxes[1][Integer.parseUnsignedInt(x.substring(2, 4), 16)];  String c = sBoxes[2][Integer.parseUnsignedInt(x.substring(4, 6), 16)];  String d = sBoxes[3][Integer.parseUnsignedInt(x.substring(6, 8), 16)];  String res = addHexMod32(a, b);  res = xor(res, c);  res = addHexMod32(res, d);  return res;  }  private String encryptBlock(String block) {  String left = block.substring(0, 8);  String right = block.substring(8, 16);  for (int i = 0; i < 16; i++) {  left = xor(left, pArray[i]);  String fOut = f(left);  right = xor(right, fOut);  // Swap left and right for next round  String temp = left;  left = right;  right = temp;  }  // Undo last swap  String temp = left;  left = right;  right = temp;  right = xor(right, pArray[16]);  left = xor(left, pArray[17]);  return left + right;  }  private String decryptBlock(String block) {  String left = block.substring(0, 8);  String right = block.substring(8, 16);  for (int i = 17; i > 1; i--) {  left = xor(left, pArray[i]);  String fOut = f(left);  right = xor(right, fOut);  // Swap left and right  String temp = left;  left = right;  right = temp;  }  // Undo last swap  String temp = left;  left = right;  right = temp;  right = xor(right, pArray[1]);  left = xor(left, pArray[0]);  return left + right;  }  // Key expansion  private void keyExpansion(String key) {  int keyLen = key.length();  int j = 0;  for (int i = 0; i < 18; i++) {  String keySegment = key.substring(j, j + 8);  pArray[i] = xor(pArray[i], keySegment);  j = (j + 8) % keyLen;  }  String block = "0000000000000000";  for (int i = 0; i < 18; i += 2) {  block = encryptBlock(block);  pArray[i] = block.substring(0, 8);  pArray[i + 1] = block.substring(8, 16);  }  for (int i = 0; i < 4; i++) {  for (int k = 0; k < 256; k += 2) {  block = encryptBlock(block);  sBoxes[i][k] = block.substring(0, 8);  sBoxes[i][k + 1] = block.substring(8, 16);  }  }  }  public static void main(String[] args) {  BlowfishDemo bf = new BlowfishDemo();  // Sample 64-bit key and plaintext (hex, 16 chars = 64 bits)  // 32 hex chars (128 bits)  String key = "0123456789abcdef0123456789abcdef";   // 64-bit plaintext block  String plaintext = "FEDCBA9876543210";  bf.keyExpansion(key);  String cipherText = bf.encryptBlock(plaintext);  System.out.println("Cipher Text: " + cipherText);  String decryptedText = bf.decryptBlock(cipherText);  System.out.println("Decrypted Text: " + decryptedText);  } }

Output:

Advantages

Blowfish is a fast block cipher except when changing keys. Each new key requires a pre-processing equivalent to 4KB of text.
It is faster and much better than DES Encryption.

Disadvantages

Blowfish uses a 64-bit block size which makes it vulnerable to birthday attacks.
A reduced round variant of blowfish is known to be susceptible to known plain text attacks(2nd order differential attacks - 4 rounds).