AES Implementation In Java with ECB | CBC | OFB | CFB Modes Of Operation

Note that these are ONLY basic level programs for easy understanding of the Advanced Encryption Standard (AES) algorithm

Key Generation - AESkeygen.java

    import java.io.File;
    import java.io.FileWriter;

    public class AESkeygen {

        private final File file = new File("AESkey.txt");
        private final int KEY_LENGTH = 32;
        private final static char[] hexArray = "0123456789ABCDEF".toCharArray();

        public AESkeygen() {
            try {
                FileWriter fileWriter = new FileWriter(file);
                fileWriter.write("");
                for (int i = 0; i < KEY_LENGTH; i++) {
                    double random = Math.random();
                    int index = (int) (random * 16);
                    fileWriter.append(hexArray[index]);
                    fileWriter.flush();
                }
                fileWriter.close();
                System.out.println("Key generated and saved in " + file.getName());
            } catch (Exception exp) {
                exp.printStackTrace();
            }
        }

        public static void main(String[] args) {
            new AESkeygen();
        }

    }

Word.java

    public class Word {

        private byte[] word = null;

        public Word() {
            word = new byte[4];
        }

        public Word(byte k0, byte k1, byte k2, byte k3) {
            this();
            word[0] = k0;
            word[1] = k1;
            word[2] = k2;
            word[3] = k3;
        }

        public byte[] getWord() {
            return word;
        }

        public void setWord(byte[] word) {
            this.word = word;
        }

        public static byte[] wordToBytes(Word word) {
            return word.getWord();
        }

        public static byte[] wordsToBytes(Word[] words) {
            byte[] out = new byte[4 * words.length];
            for (int i = 0; i < words.length; i++) {
                byte[] temp = words[i].getWord();
                out[4 * i] = temp[0];
                out[4 * i + 1] = temp[1];
                out[4 * i + 2] = temp[2];
                out[4 * i + 3] = temp[3];
            }
            return out;
        }

        public void rotWord() {
            byte[] temp = this.getWord();
            byte[] newWord = new byte[4];
            newWord[0] = temp[1];
            newWord[1] = temp[2];
            newWord[2] = temp[3];
            newWord[3] = temp[0];
            this.setWord(newWord);
        }

        public void subWord() {
            byte[] in = this.getWord();
            byte[] out = new byte[4];
            for (int i = 0; i < 4; i++) {
                byte a = in[i];
                int row = (a >> 4) & 0x000F;
                int col = a & 0x000F;
                out[i] = (byte) AESencrypt.sBox[row * 16 + col];
            }
            for (int i = 0; i < 4; i++) {
                this.word[i] = out[i];
            }
        }

        public static Word XORWords(Word word1, Word word2) {
            Word outWord = new Word();
            byte[] in1 = word1.getWord();
            byte[] in2 = word2.getWord();
            byte[] out = new byte[4];
            for (int i = 0; i < 4; i++) {
                out[i] = (byte) ((in1[i] ^ in2[i]) & 0xff);
            }
            outWord.setWord(out);
            return outWord;
        }

        public String toString() {
            return AESencrypt.bytesToHex(this.getWord());
        }
    }

  

Encryption - AESencrypt.java

        
    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.FileReader;
    import java.util.Arrays;

    public class AESencrypt {

        private static final int BITS = 16;
        private static final int ROUNDS = 10;
        private static final int NO_OF_WORDS_IN_KEY = 44;
        private static final int KEY_LENGTH = 16;
        private static final int BLOCK_LENGTH = 16;
        final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();
        int[] RC = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1B, 0x36 };
        Word[] Rcon = new Word[ROUNDS];
        private byte[] word = null;
        private String mode = null;
         
        static final int[] sBox = {
          0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
          0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
          0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
          0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
          0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
          0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
          0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
          0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
          0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
          0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
          0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
          0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
          0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
          0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
          0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
          0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16
        };
          
        static final int[] invSBox = {
          0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
          0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
          0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
          0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25, 
          0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92, 
          0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84, 
          0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06, 
          0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b, 
          0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73, 
          0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e, 
          0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b, 
          0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4, 
          0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f, 
          0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef, 
          0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61, 
          0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d
        };                   

        
        public AESencrypt(String mode) {
            this.mode = mode;
            for (int i = 0; i < ROUNDS; i++) {
                Rcon[i] = new Word();
                byte[] temp = new byte[4];
                temp[0] = (byte) (RC[i] & 0xff);
                temp[1] = 0;
                temp[2] = 0;
                temp[3] = 0;
                Rcon[i].setWord(temp);
            }
            word = new byte[NO_OF_WORDS_IN_KEY];
        }

        /* Ref: http://www.samiam.org/galois.html */
        /* Galois Addition */
        byte gadd(byte a, byte b) {
            return (byte) ((a ^ b) & 0xff);
        }

        /* Galois Subtraction */
        byte gsub(byte a, byte b) {
            return (byte) ((a ^ b) & 0xff);
        }

        /* Galois Multiplication */
        byte gmul(byte a, byte b) {
            byte p = 0;
            int counter;
            byte high_bit_set;
            byte byte0x80 = hexStringToByteArray("80")[0];
            for (counter = 0; counter < 8; counter++) {
                if ((b & 0x01) == 1) {
                    // System.out.println("lower bit of b is set");
                    p = (byte) ((p ^ a) & 0xff);
                }
                high_bit_set = (byte) (a & 0x80);
                // printByte("high_bit_set", high_bit_set);
                a <<= 1;
                if (high_bit_set == byte0x80) {
                    // System.out.println("higher bit of a is set");
                    a = (byte) ((a ^ 0x1b) & 0xff);
                }
                b = (byte) ((b >> 1) & 0x7f);

                // printByte("a", a);
                // printByte("b", b);
                // printByte("p", p);
            }
            return p;
        }

        byte gmul(byte a, int b) {
            byte t = (byte) (b & 0xff);
            return gmul(a, t);
        }

        /* Key Expansion */
        private byte[] expandKey(byte[] key) throws Exception {
            // System.out.println(key.length);
            // System.out.println(bytesToHex(key));
            if (key.length != KEY_LENGTH) {
                throw new Exception("Key should be of length, 128 bits");
            }
            Word[] w = new Word[NO_OF_WORDS_IN_KEY];
            Word temp;
            for (int i = 0; i < 4; i++) {
                w[i] = new Word(key[4 * i], key[4 * i + 1], key[4 * i + 2], key[4 * i + 3]);
                // System.out.println("w" + i + " = " + w[i]);
            }

            for (int i = 4; i < 44; i++) {
                temp = w[i - 1];
                Word temp1 = new Word();
                temp1.setWord(temp.getWord());
                // System.out.println("w" + (i-1) + " = " + temp);
                if (i % 4 == 0) {
                    temp1.rotWord();
                    // System.out.println("Rot=" + temp1);
                    temp1.subWord();
                    // System.out.println("Sub=" + temp1);
                    temp1 = Word.XORWords(temp1, Rcon[(i / 4) - 1]);
                    // System.out.println("Rcon" + temp1);
                }
                w[i] = Word.XORWords(w[i - 4], temp1);
                // System.out.println("w" + i + " = " + w[i]);
            }
            return Word.wordsToBytes(w);
        }

        /* Substitute Bytes */
        private byte[] subBytes(byte[] in) {
            byte[] out = new byte[BITS];
            for (int i = 0; i < BITS; i++) {
                byte a = in[i];
                int row = (a >> 4) & 0x000F;
                int col = a & 0x000F;
                out[i] = (byte) sBox[row * BITS + col];
            }
            return out;
        }

        /* Inverse Substitute Bytes */
        private byte[] inverseSubBytes(byte[] in) {
            byte[] out = new byte[BITS];
            for (int i = 0; i < BITS; i++) {
                byte a = in[i];
                int row = (a >> 4) & 0x000F;
                int col = a & 0x000F;
                out[i] = (byte) invSBox[row * BITS + col];
            }
            return out;
        }

        /* Shift Rows */
        private byte[] shiftRows(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            // System.out.println("temp: " + bytesToHex(temp));
            for (int i = 0; i < BITS / 4; i++) {
                byte[] a = Arrays.copyOfRange(temp, (4 * i), (4 * i + 4));
                byte[] b = leftShift(a, i);
                in[4 * i] = b[0];
                in[4 * i + 1] = b[1];
                in[4 * i + 2] = b[2];
                in[4 * i + 3] = b[3];
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    out[4 * j + i] = in[4 * i + j];
                }
            }
            return out;
        }

        private byte[] leftShift(byte[] in, int times) {
            byte[] out = new byte[4];
            out = Arrays.copyOfRange(in, 0, 4);
            for (int i = 0; i < times; i++) {
                out[0] = in[1];
                out[1] = in[2];
                out[2] = in[3];
                out[3] = in[0];
                in = Arrays.copyOfRange(out, 0, 4);
            }
            return out;
        }

        /* Inverse Shift Rows */
        private byte[] inverseShiftRows(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            for (int i = 0; i < BITS / 4; i++) {
                byte[] a = Arrays.copyOfRange(temp, (4 * i), (4 * i + 4));
                byte[] b = rightShift(a, i);
                in[4 * i] = b[0];
                in[4 * i + 1] = b[1];
                in[4 * i + 2] = b[2];
                in[4 * i + 3] = b[3];
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    out[4 * j + i] = in[4 * i + j];
                }
            }
            return out;
        }

        private byte[] rightShift(byte[] in, int times) {
            byte[] out = new byte[4];
            out = Arrays.copyOfRange(in, 0, 4);
            for (int i = 0; i < times; i++) {
                out[0] = in[3];
                out[1] = in[0];
                out[2] = in[1];
                out[3] = in[2];
                in = Arrays.copyOfRange(out, 0, 4);
            }
            return out;
        }

        /* Mix Columns */
        private byte[] mixColumns(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            in = temp;
            for (int j = 0; j < BITS / 4; j++) {
                out[4 * 0 + j] = (byte) ((gmul(in[4 * 0 + j], 2) ^ gmul(in[4 * 1 + j], 3) ^ in[4 * 2 + j] ^ in[4 * 3 + j])
                        & 0xff);
                out[4 * 1 + j] = (byte) ((in[4 * 0 + j] ^ gmul(in[4 * 1 + j], 2) ^ gmul(in[4 * 2 + j], 3) ^ in[4 * 3 + j])
                        & 0xff);
                out[4 * 2 + j] = (byte) ((in[4 * 0 + j] ^ in[4 * 1 + j] ^ gmul(in[4 * 2 + j], 2) ^ gmul(in[4 * 3 + j], 3))
                        & 0xff);
                out[4 * 3 + j] = (byte) ((gmul(in[4 * 0 + j], 3) ^ in[4 * 1 + j] ^ in[4 * 2 + j] ^ gmul(in[4 * 3 + j], 2))
                        & 0xff);
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = out[4 * i + j];
                }
            }
            out = temp;
            return out;
        }

        /* Inverse Mix Columns */
        private byte[] inverseMixColumns(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            in = temp;
            for (int j = 0; j < BITS / 4; j++) {
                out[4 * 0 + j] = (byte) ((gmul(in[4 * 0 + j], 14) ^ gmul(in[4 * 1 + j], 11) ^ gmul(in[4 * 2 + j], 13)
                        ^ gmul(in[4 * 3 + j], 9)) & 0xff);
                out[4 * 1 + j] = (byte) ((gmul(in[4 * 0 + j], 9) ^ gmul(in[4 * 1 + j], 14) ^ gmul(in[4 * 2 + j], 11)
                        ^ gmul(in[4 * 3 + j], 13)) & 0xff);
                out[4 * 2 + j] = (byte) ((gmul(in[4 * 0 + j], 13) ^ gmul(in[4 * 1 + j], 9) ^ gmul(in[4 * 2 + j], 14)
                        ^ gmul(in[4 * 3 + j], 11)) & 0xff);
                out[4 * 3 + j] = (byte) ((gmul(in[4 * 0 + j], 11) ^ gmul(in[4 * 1 + j], 13) ^ gmul(in[4 * 2 + j], 9)
                        ^ gmul(in[4 * 3 + j], 14)) & 0xff);
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = out[4 * i + j];
                }
            }
            out = temp;
            return out;
        }

        private byte[] hexStringToByteArray(String string) {
            int length = string.length();
            int n = (int) Math.ceil((length + 1) / 2);
            byte[] result = new byte[n];
            for (int i = length - 1; i >= 0; i -= 2) {
                if (i == 0) {
                    result[i / 2] = (byte) ((Character.digit('0', 16) << 4) + Character.digit(string.charAt(i), 16));
                } else {
                    result[i / 2] = (byte) ((Character.digit(string.charAt(i - 1), 16) << 4)
                            + Character.digit(string.charAt(i), 16));
                }
            }
            return result;
        }

        /*
         * http://stackoverflow.com/questions/9655181/convert-from-byte-array-to-hex-
         * string-in-java
         */
        public static String bytesToHex(byte[] bytes) {
            char[] hexChars = new char[bytes.length * 2];
            for (int j = 0; j < bytes.length; j++) {
                int v = bytes[j] & 0xFF;
                hexChars[j * 2] = hexArray[v >>> 4];
                hexChars[j * 2 + 1] = hexArray[v & 0x0F];
            }
            return new String(hexChars);
        }

        private void printBytes(byte[] input) {
            for (int i = 0; i < input.length; i++) {
                System.out.print(byteToBits(input[i]) + " ");
            }
            System.out.println();
        }

        private void printByte(String msg, byte input) {
            byte[] temp = new byte[1];
            temp[0] = input;
            System.out.println(msg + ": " + bytesToHex(temp));
        }

        private String byteToBits(byte b) {
            StringBuffer buffer = new StringBuffer();
            for (int i = 0; i < 8; i++)
                buffer.append((int) (b >> (8 - (i + 1)) & 0x0001));
            return buffer.toString();
        }

        private byte[] getRoundKey(int round) {
            byte[] out = new byte[KEY_LENGTH];
            out = Arrays.copyOfRange(word, 16 * round, 16 * round + 16);
            return out;
        }

        public static byte[] XORBytes(byte[] in1, byte[] in2) {
            byte[] out = new byte[in1.length];
            for (int i = 0; i < in1.length; i++) {
                out[i] = (byte) ((in1[i] ^ in2[i]) & 0xff);
            }
            return out;
        }

        public byte[] encryptText(byte[] plainText, byte[] key) throws Exception {
            byte[] cipher = new byte[BLOCK_LENGTH];
            this.word = expandKey(key);
            byte[] roundKey = getRoundKey(0);
            /* Round 0 */
            cipher = XORBytes(plainText, roundKey);
            // System.out.println("Round 0\n" + bytesToHex(cipher));
            /* Rounds 1 to 9 */
            for (int i = 1; i < 10; i++) {
                // System.out.println("Round " + i);
                cipher = subBytes(cipher);
                // System.out.println("SubBytes: " + bytesToHex(cipher));
                cipher = shiftRows(cipher);
                // System.out.println("ShiftRows: " + bytesToHex(cipher));
                cipher = mixColumns(cipher);
                // System.out.println("MixColumns: " + bytesToHex(cipher));
                roundKey = getRoundKey(i);
                // System.out.println("RoundKey: " + bytesToHex(roundKey));
                cipher = XORBytes(cipher, roundKey);
                // System.out.println("CIPHER: " + bytesToHex(cipher));
            }
            /* Round 10 */
            // System.out.println("Round 10");
            cipher = subBytes(cipher);
            // System.out.println("SubBytes: " + bytesToHex(cipher));
            cipher = shiftRows(cipher);
            // System.out.println("ShiftRows: " + bytesToHex(cipher));
            roundKey = getRoundKey(10);
            // System.out.println("RoundKey: " + bytesToHex(roundKey));
            cipher = XORBytes(cipher, roundKey);
            // System.out.println("CIPHER: " + bytesToHex(cipher));
            return cipher;
        }

        public byte[] decryptText(byte[] cipher, byte[] key) throws Exception {
            byte[] plainText = new byte[BLOCK_LENGTH];
            this.word = expandKey(key);
            byte[] roundKey = getRoundKey(10);
            /* Round 0 */
            plainText = XORBytes(cipher, roundKey);
            /* Rounds 1 to 9 */
            for (int i = 9; i > 0; i--) {
                plainText = inverseShiftRows(plainText);
                plainText = inverseSubBytes(plainText);
                roundKey = getRoundKey(i);
                plainText = XORBytes(plainText, roundKey);
                plainText = inverseMixColumns(plainText);
            }
            /* Round 10 */
            plainText = inverseShiftRows(plainText);
            plainText = inverseSubBytes(plainText);
            roundKey = getRoundKey(0);
            plainText = XORBytes(plainText, roundKey);
            return plainText;
        }

        public static void main(String[] args) throws Exception {
            try {
                if (args.length != 1) {
                    System.out.println("Usage: java < classname > < mode >" + "\n\t< mode > := (ECB|CBC|OFB|CFB)");
                    return;
                }
                /* ECB, CBC, OFB, or CFB */
                String mode = args[0];
                // String mode = "CFB";
                mode = mode.toUpperCase();
                AESencrypt aes = new AESencrypt(mode);
                File keyFile = new File("AESkey.txt");
                File textFile = new File("AESplaintext.txt");
                File cipherFile = new File("AESciphertext.txt");
                FileReader keyFileReader = new FileReader(keyFile);
                BufferedReader bufferedReader = new BufferedReader(keyFileReader);
                FileInputStream textFileInputStream = new FileInputStream(textFile);
                FileOutputStream cipherFileOutputStream = new FileOutputStream(cipherFile);
                byte[] key = new byte[(int) keyFile.length()];
                String keyString = bufferedReader.readLine();
                key = aes.hexStringToByteArray(keyString);
                byte[] message = new byte[(int) textFile.length()];
                textFileInputStream.read(message);
                byte[] cipher = aes.encrypt(message, key);
                cipherFileOutputStream.write(cipher);
                cipherFileOutputStream.flush();
                cipherFileOutputStream.close();
                bufferedReader.close();
                textFileInputStream.close();
                System.out.println("Encryption done! Please check AESciphertext.txt for output!");
            } catch (Exception exp) {
                exp.printStackTrace();
            }
        }

        private byte[] encrypt(byte[] message, byte[] key) throws Exception {
            if (message.length < 16) {
                System.out.println("Message should be atleast 64 bits");
                System.exit(1);
            }
            if (key.length != 16) {
                System.out.println("Key should be 64 bits");
                System.exit(1);
            }
            int length = message.length;
            int n = (length + 15) / 16 * 16;
            byte[] cipher = new byte[n];
            if (length == 16) {
                if (mode.equals("ECB")) {
                    return encryptText(message, key);
                } else if (mode.equals("CBC")) {
                    byte[] iv = getInitializationVector();
                    message = XORBytes(message, iv);
                    return encryptText(message, key);
                } else if (mode.equals("OFB")) {
                    byte[] nounce = getNounce();
                    byte[] temp = encryptText(nounce, key);
                    byte[] result = XORBytes(temp, message);
                    return result;
                } else if (mode.equals("CFB")) {

                } else {
                    System.out.println("Unsupported mode of operation!");
                    return null;
                }
            }
            int i = 0;
            int k = 0;
            byte[] feedback = new byte[16];
            if (mode.equals("CBC")) {
                feedback = getInitializationVector();
            } else if (mode.equals("OFB")) {
                feedback = getNounce();
            } else if (mode.equals("CFB")) {
                feedback = getInitializationVectorCFB();
            }

            while (i < length) {
                byte[] block = new byte[16];
                byte[] result = new byte[16];
                int j = 0;
                for (; j < 16 && i < length; j++, i++) {
                    block[j] = message[i];
                }
                while (j < 16) {
                    /* pad with white spaces */
                    block[j++] = 0x20;
                }

                // System.out.println("BLOCK: ");
                // printBytes(block);
                if (mode.equals("ECB")) {
                    result = encryptText(block, key);
                } else if (mode.equals("CBC")) {
                    block = XORBytes(block, feedback);
                    result = encryptText(block, key);
                    feedback = Arrays.copyOfRange(result, 0, 16);
                } else if (mode.equals("OFB")) {
                    result = encryptText(feedback, key);
                    feedback = Arrays.copyOfRange(result, 0, 16);
                    result = XORBytes(result, block);
                } else if (mode.equals("CFB")) {
                    result = encryptText(feedback, key);
                    byte[] resultPart = Arrays.copyOfRange(result, 0, 8);
                    byte[] blockPart = Arrays.copyOfRange(block, 0, 8);
                    byte[] temp1 = XORBytes(resultPart, blockPart);
                    feedback = mergeBytes(Arrays.copyOfRange(result, 8, 16), temp1);
                    resultPart = Arrays.copyOfRange(result, 8, 16);
                    blockPart = Arrays.copyOfRange(block, 8, 16);
                    result = encryptText(feedback, key);
                    byte[] temp2 = XORBytes(resultPart, blockPart);
                    feedback = mergeBytes(Arrays.copyOfRange(result, 8, 16), temp2);
                    result = mergeBytes(temp1, temp2);
                } else {
                    System.out.println("Unsupported mode of operation!");
                    return null;
                }
                // System.out.println("RESULT: ");
                // printBytes(result);
                for (j = 0; j < 16 && k < cipher.length; j++, k++) {
                    cipher[k] = result[j];
                }
            }
            return cipher;
        }

        private byte[] getInitializationVector() {
            return hexStringToByteArray("247D8AC4DDB1AA739DC593821D0BC432");
        }

        private byte[] getInitializationVectorCFB() {
            return hexStringToByteArray("247D8AC4DDB1AA739DC593821D0BC432");
        }

        private byte[] getNounce() {
            // char[] hexArray = "0123456789ABCDEF".toCharArray();
            // String nounceStr = "";
            // for (int i = 0 ; i < 16 ; i++) {
            // double random = Math.random();
            // int index = (int) (random * 16);
            // nounceStr += hexArray[index];
            // }
            // return hexStringToByteArray(nounceStr);
            return hexStringToByteArray("247D8AC4DDB1AA739DC593821D0BC432");
        }

        private byte[] mergeBytes(byte[] in1, byte[] in2) {
            byte[] out = new byte[in1.length + in2.length];
            int i = 0;
            for (int j = 0; j < in1.length; j++) {
                out[i++] = in1[j];
            }
            for (int j = 0; j < in2.length; j++) {
                out[i++] = in2[j];
            }
            return out;
        }
    }

Decryption - AESdecrypt.java

    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.FileReader;
    import java.util.Arrays;

    public class AESdecrypt {

        private static final int BITS = 16;
        private static final int ROUNDS = 10;
        private static final int NO_OF_WORDS_IN_KEY = 44;
        private static final int KEY_LENGTH = 16;
        private static final int BLOCK_LENGTH = 16;
        final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();
        int[] RC = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1B, 0x36 };
        Word[] Rcon = new Word[ROUNDS];
        private byte[] word = null;
        private String mode = null;
         
        static final int[] sBox = {
          0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
          0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
          0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
          0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
          0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
          0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
          0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
          0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
          0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
          0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
          0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
          0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
          0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
          0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
          0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
          0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16
        };
          
        static final int[] invSBox = {
          0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
          0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
          0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
          0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25, 
          0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92, 
          0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84, 
          0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06, 
          0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b, 
          0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73, 
          0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e, 
          0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b, 
          0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4, 
          0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f, 
          0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef, 
          0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61, 
          0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d
        };


        public AESdecrypt(String mode) {
            this.mode = mode;
            for (int i = 0; i < ROUNDS; i++) {
                Rcon[i] = new Word();
                byte[] temp = new byte[4];
                temp[0] = (byte) (RC[i] & 0xff);
                temp[1] = 0;
                temp[2] = 0;
                temp[3] = 0;
                Rcon[i].setWord(temp);
            }
            word = new byte[NO_OF_WORDS_IN_KEY];
        }

        /* Ref: http://www.samiam.org/galois.html */
        /* Galois Addition */
        byte gadd(byte a, byte b) {
            return (byte) ((a ^ b) & 0xff);
        }

        /* Galois Subtraction */
        byte gsub(byte a, byte b) {
            return (byte) ((a ^ b) & 0xff);
        }

        /* Galois Multiplication */
        byte gmul(byte a, byte b) {
            byte p = 0;
            int counter;
            byte high_bit_set;
            byte byte0x80 = hexStringToByteArray("80")[0];
            for (counter = 0; counter < 8; counter++) {
                if ((b & 0x01) == 1) {
                    // System.out.println("lower bit of b is set");
                    p = (byte) ((p ^ a) & 0xff);
                }
                high_bit_set = (byte) (a & 0x80);
                // printByte("high_bit_set", high_bit_set);
                a <<= 1;
                if (high_bit_set == byte0x80) {
                    // System.out.println("higher bit of a is set");
                    a = (byte) ((a ^ 0x1b) & 0xff);
                }
                b = (byte) ((b >> 1) & 0x7f);

                // printByte("a", a);
                // printByte("b", b);
                // printByte("p", p);
            }
            return p;
        }

        byte gmul(byte a, int b) {
            byte t = (byte) (b & 0xff);
            return gmul(a, t);
        }

        /* Key Expansion */
        private byte[] expandKey(byte[] key) throws Exception {
            // System.out.println(key.length);
            // System.out.println(bytesToHex(key));
            if (key.length != KEY_LENGTH) {
                throw new Exception("Key should be of length, 128 bits");
            }
            Word[] w = new Word[NO_OF_WORDS_IN_KEY];
            Word temp;
            for (int i = 0; i < 4; i++) {
                w[i] = new Word(key[4 * i], key[4 * i + 1], key[4 * i + 2], key[4 * i + 3]);
                // System.out.println("w" + i + " = " + w[i]);
            }

            for (int i = 4; i < 44; i++) {
                temp = w[i - 1];
                Word temp1 = new Word();
                temp1.setWord(temp.getWord());
                // System.out.println("w" + (i-1) + " = " + temp);
                if (i % 4 == 0) {
                    temp1.rotWord();
                    // System.out.println("Rot=" + temp1);
                    temp1.subWord();
                    // System.out.println("Sub=" + temp1);
                    temp1 = Word.XORWords(temp1, Rcon[(i / 4) - 1]);
                    // System.out.println("Rcon" + temp1);
                }
                w[i] = Word.XORWords(w[i - 4], temp1);
                // System.out.println("w" + i + " = " + w[i]);
            }
            return Word.wordsToBytes(w);
        }

        /* Substitute Bytes */
        private byte[] subBytes(byte[] in) {
            byte[] out = new byte[BITS];
            for (int i = 0; i < BITS; i++) {
                byte a = in[i];
                int row = (a >> 4) & 0x000F;
                int col = a & 0x000F;
                out[i] = (byte) sBox[row * BITS + col];
            }
            return out;
        }

        /* Inverse Substitute Bytes */
        private byte[] inverseSubBytes(byte[] in) {
            byte[] out = new byte[BITS];
            for (int i = 0; i < BITS; i++) {
                byte a = in[i];
                int row = (a >> 4) & 0x000F;
                int col = a & 0x000F;
                out[i] = (byte) invSBox[row * BITS + col];
            }
            return out;
        }

        /* Shift Rows */
        private byte[] shiftRows(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            // System.out.println("temp: " + bytesToHex(temp));
            for (int i = 0; i < BITS / 4; i++) {
                byte[] a = Arrays.copyOfRange(temp, (4 * i), (4 * i + 4));
                byte[] b = leftShift(a, i);
                in[4 * i] = b[0];
                in[4 * i + 1] = b[1];
                in[4 * i + 2] = b[2];
                in[4 * i + 3] = b[3];
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    out[4 * j + i] = in[4 * i + j];
                }
            }
            return out;
        }

        private byte[] leftShift(byte[] in, int times) {
            byte[] out = new byte[4];
            out = Arrays.copyOfRange(in, 0, 4);
            for (int i = 0; i < times; i++) {
                out[0] = in[1];
                out[1] = in[2];
                out[2] = in[3];
                out[3] = in[0];
                in = Arrays.copyOfRange(out, 0, 4);
            }
            return out;
        }

        /* Inverse Shift Rows */
        private byte[] inverseShiftRows(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            for (int i = 0; i < BITS / 4; i++) {
                byte[] a = Arrays.copyOfRange(temp, (4 * i), (4 * i + 4));
                byte[] b = rightShift(a, i);
                in[4 * i] = b[0];
                in[4 * i + 1] = b[1];
                in[4 * i + 2] = b[2];
                in[4 * i + 3] = b[3];
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    out[4 * j + i] = in[4 * i + j];
                }
            }
            return out;
        }

        private byte[] rightShift(byte[] in, int times) {
            byte[] out = new byte[4];
            out = Arrays.copyOfRange(in, 0, 4);
            for (int i = 0; i < times; i++) {
                out[0] = in[3];
                out[1] = in[0];
                out[2] = in[1];
                out[3] = in[2];
                in = Arrays.copyOfRange(out, 0, 4);
            }
            return out;
        }

        /* Mix Columns */
        private byte[] mixColumns(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            in = temp;
            for (int j = 0; j < BITS / 4; j++) {
                out[4 * 0 + j] = (byte) ((gmul(in[4 * 0 + j], 2) ^ gmul(in[4 * 1 + j], 3) ^ in[4 * 2 + j] ^ in[4 * 3 + j])
                        & 0xff);
                out[4 * 1 + j] = (byte) ((in[4 * 0 + j] ^ gmul(in[4 * 1 + j], 2) ^ gmul(in[4 * 2 + j], 3) ^ in[4 * 3 + j])
                        & 0xff);
                out[4 * 2 + j] = (byte) ((in[4 * 0 + j] ^ in[4 * 1 + j] ^ gmul(in[4 * 2 + j], 2) ^ gmul(in[4 * 3 + j], 3))
                        & 0xff);
                out[4 * 3 + j] = (byte) ((gmul(in[4 * 0 + j], 3) ^ in[4 * 1 + j] ^ in[4 * 2 + j] ^ gmul(in[4 * 3 + j], 2))
                        & 0xff);
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = out[4 * i + j];
                }
            }
            out = temp;
            return out;
        }

        /* Inverse Mix Columns */
        private byte[] inverseMixColumns(byte[] in) {
            byte[] out = new byte[BITS];
            byte[] temp = new byte[BITS];
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = in[4 * i + j];
                }
            }
            in = temp;
            for (int j = 0; j < BITS / 4; j++) {
                out[4 * 0 + j] = (byte) ((gmul(in[4 * 0 + j], 14) ^ gmul(in[4 * 1 + j], 11) ^ gmul(in[4 * 2 + j], 13)
                        ^ gmul(in[4 * 3 + j], 9)) & 0xff);
                out[4 * 1 + j] = (byte) ((gmul(in[4 * 0 + j], 9) ^ gmul(in[4 * 1 + j], 14) ^ gmul(in[4 * 2 + j], 11)
                        ^ gmul(in[4 * 3 + j], 13)) & 0xff);
                out[4 * 2 + j] = (byte) ((gmul(in[4 * 0 + j], 13) ^ gmul(in[4 * 1 + j], 9) ^ gmul(in[4 * 2 + j], 14)
                        ^ gmul(in[4 * 3 + j], 11)) & 0xff);
                out[4 * 3 + j] = (byte) ((gmul(in[4 * 0 + j], 11) ^ gmul(in[4 * 1 + j], 13) ^ gmul(in[4 * 2 + j], 9)
                        ^ gmul(in[4 * 3 + j], 14)) & 0xff);
            }
            for (int i = 0; i < BITS / 4; i++) {
                for (int j = 0; j < BITS / 4; j++) {
                    temp[4 * j + i] = out[4 * i + j];
                }
            }
            out = temp;
            return out;
        }

        private byte[] hexStringToByteArray(String string) {
            int length = string.length();
            int n = (int) Math.ceil((length + 1) / 2);
            byte[] result = new byte[n];
            for (int i = length - 1; i >= 0; i -= 2) {
                if (i == 0) {
                    result[i / 2] = (byte) ((Character.digit('0', 16) << 4) + Character.digit(string.charAt(i), 16));
                } else {
                    result[i / 2] = (byte) ((Character.digit(string.charAt(i - 1), 16) << 4)
                            + Character.digit(string.charAt(i), 16));
                }
            }
            return result;
        }

        /*
         * http://stackoverflow.com/questions/9655181/convert-from-byte-array-to-hex-
         * string-in-java
         */
        public static String bytesToHex(byte[] bytes) {
            char[] hexChars = new char[bytes.length * 2];
            for (int j = 0; j < bytes.length; j++) {
                int v = bytes[j] & 0xFF;
                hexChars[j * 2] = hexArray[v >>> 4];
                hexChars[j * 2 + 1] = hexArray[v & 0x0F];
            }
            return new String(hexChars);
        }

        private void printBytes(byte[] input) {
            for (int i = 0; i < input.length; i++) {
                System.out.print(byteToBits(input[i]) + " ");
            }
            System.out.println();
        }

        private void printByte(String msg, byte input) {
            byte[] temp = new byte[1];
            temp[0] = input;
            System.out.println(msg + ": " + bytesToHex(temp));
        }

        private String byteToBits(byte b) {
            StringBuffer buffer = new StringBuffer();
            for (int i = 0; i < 8; i++)
                buffer.append((int) (b >> (8 - (i + 1)) & 0x0001));
            return buffer.toString();
        }

        private byte[] getRoundKey(int round) {
            byte[] out = new byte[KEY_LENGTH];
            out = Arrays.copyOfRange(word, 16 * round, 16 * round + 16);
            return out;
        }

        public static byte[] XORBytes(byte[] in1, byte[] in2) {
            byte[] out = new byte[in1.length];
            for (int i = 0; i < in1.length; i++) {
                out[i] = (byte) ((in1[i] ^ in2[i]) & 0xff);
            }
            return out;
        }

        public byte[] encryptText(byte[] plainText, byte[] key) throws Exception {
            byte[] cipher = new byte[BLOCK_LENGTH];
            this.word = expandKey(key);
            byte[] roundKey = getRoundKey(0);
            /* Round 0 */
            cipher = XORBytes(plainText, roundKey);
            // System.out.println("Round 0\n" + bytesToHex(cipher));
            /* Rounds 1 to 9 */
            for (int i = 1; i < 10; i++) {
                // System.out.println("Round " + i);
                cipher = subBytes(cipher);
                // System.out.println("SubBytes: " + bytesToHex(cipher));
                cipher = shiftRows(cipher);
                // System.out.println("ShiftRows: " + bytesToHex(cipher));
                cipher = mixColumns(cipher);
                // System.out.println("MixColumns: " + bytesToHex(cipher));
                roundKey = getRoundKey(i);
                // System.out.println("RoundKey: " + bytesToHex(roundKey));
                cipher = XORBytes(cipher, roundKey);
                // System.out.println("CIPHER: " + bytesToHex(cipher));
            }
            /* Round 10 */
            // System.out.println("Round 10");
            cipher = subBytes(cipher);
            // System.out.println("SubBytes: " + bytesToHex(cipher));
            cipher = shiftRows(cipher);
            // System.out.println("ShiftRows: " + bytesToHex(cipher));
            roundKey = getRoundKey(10);
            // System.out.println("RoundKey: " + bytesToHex(roundKey));
            cipher = XORBytes(cipher, roundKey);
            // System.out.println("CIPHER: " + bytesToHex(cipher));
            return cipher;
        }

        public byte[] decryptText(byte[] cipher, byte[] key) throws Exception {
            byte[] plainText = new byte[BLOCK_LENGTH];
            this.word = expandKey(key);
            byte[] roundKey = getRoundKey(10);
            /* Round 0 */
            plainText = XORBytes(cipher, roundKey);
            /* Rounds 1 to 9 */
            for (int i = 9; i > 0; i--) {
                plainText = inverseShiftRows(plainText);
                plainText = inverseSubBytes(plainText);
                roundKey = getRoundKey(i);
                plainText = XORBytes(plainText, roundKey);
                plainText = inverseMixColumns(plainText);
            }
            /* Round 10 */
            plainText = inverseShiftRows(plainText);
            plainText = inverseSubBytes(plainText);
            roundKey = getRoundKey(0);
            plainText = XORBytes(plainText, roundKey);
            return plainText;
        }

        public static void main(String[] args) throws Exception {
            try {
                if (args.length != 1) {
                    System.out.println("Usage: java < classname > < mode >" + "\n\t< mode > := (ECB|CBC|OFB|CFB)");
                    return;
                }
                /* ECB, CBC, OFB, or CFB */
                String mode = args[0];
                // String mode = "CFB";
                mode = mode.toUpperCase();
                AESdecrypt aes = new AESdecrypt(mode);
                File keyFile = new File("AESkey.txt");
                File textFile = new File("AESplaintext.txt");
                File cipherFile = new File("AESciphertext.txt");
                FileReader keyFileReader = new FileReader(keyFile);
                BufferedReader bufferedReader = new BufferedReader(keyFileReader);
                FileInputStream cipherFileInputStream = new FileInputStream(cipherFile);
                FileOutputStream textFileOutputStream = new FileOutputStream(textFile);
                byte[] key = new byte[(int) keyFile.length()];
                String keyString = bufferedReader.readLine();
                key = aes.hexStringToByteArray(keyString);
                byte[] cipher = new byte[(int) cipherFile.length()];
                cipherFileInputStream.read(cipher);
                byte[] message = aes.decrypt(cipher, key);
                textFileOutputStream.write(message);
                textFileOutputStream.flush();
                textFileOutputStream.close();
                bufferedReader.close();
                cipherFileInputStream.close();
                System.out.println("Decryption done! Please check AESplaintext.txt for output!");
            } catch (Exception exp) {
                exp.printStackTrace();
            }
        }

        private byte[] decrypt(byte[] message, byte[] key) throws Exception {
            if (message.length < 16) {
                System.out.println("Message should be atleast 64 bits");
                System.exit(1);
            }
            if (key.length != 16) {
                System.out.println("Key should be 64 bits");
                System.exit(1);
            }
            int length = message.length;
            int n = (length + 15) / 16 * 16;
            byte[] cipher = new byte[n];
            if (length == 16) {
                if (mode.equals("ECB")) {
                    return decryptText(message, key);
                } else if (mode.equals("CBC")) {
                    byte[] iv = getInitializationVector();
                    message = XORBytes(message, iv);
                    return decryptText(message, key);
                } else if (mode.equals("OFB")) {
                    byte[] nounce = getNounce();
                    byte[] temp = encryptText(nounce, key);
                    byte[] result = XORBytes(temp, message);
                    return result;
                } else if (mode.equals("CFB")) {

                } else {
                    System.out.println("Unsupported mode of operation!");
                    return null;
                }
            }
            int i = 0;
            int k = 0;
            byte[] feedback = new byte[16];
            if (mode.equals("CBC")) {
                feedback = getInitializationVector();
            } else if (mode.equals("OFB")) {
                feedback = getNounce();
            } else if (mode.equals("CFB")) {
                feedback = getInitializationVectorCFB();
            }

            while (i < length) {
                byte[] block = new byte[16];
                byte[] result = new byte[16];
                int j = 0;
                for (; j < 16 && i < length; j++, i++) {
                    block[j] = message[i];
                }
                while (j < 16) {
                    /* pad with white spaces */
                    block[j++] = 0x20;
                }

                // System.out.println("BLOCK: ");
                // printBytes(block);
                if (mode.equals("ECB")) {
                    result = decryptText(block, key);
                } else if (mode.equals("CBC")) {
                    result = decryptText(block, key);
                    result = XORBytes(result, feedback);
                    feedback = Arrays.copyOfRange(block, 0, 16);
                } else if (mode.equals("OFB")) {
                    result = encryptText(feedback, key);
                    feedback = Arrays.copyOfRange(result, 0, 16);
                    result = XORBytes(result, block);
                } else if (mode.equals("CFB")) {
                    result = encryptText(feedback, key);
                    byte[] resultPart = Arrays.copyOfRange(result, 0, 8);
                    byte[] blockPart = Arrays.copyOfRange(block, 0, 8);
                    byte[] temp1 = XORBytes(resultPart, blockPart);
                    feedback = mergeBytes(Arrays.copyOfRange(result, 8, 16), blockPart);
                    resultPart = Arrays.copyOfRange(result, 8, 16);
                    blockPart = Arrays.copyOfRange(block, 8, 16);
                    result = encryptText(feedback, key);
                    byte[] temp2 = XORBytes(resultPart, blockPart);
                    feedback = mergeBytes(Arrays.copyOfRange(result, 8, 16), blockPart);
                    result = mergeBytes(temp1, temp2);
                } else {
                    System.out.println("Unsupported mode of operation!");
                    return null;
                }
                // System.out.println("RESULT: ");
                // printBytes(result);
                for (j = 0; j < 16 && k < cipher.length; j++, k++) {
                    cipher[k] = result[j];
                }
            }
            return cipher;
        }

        private byte[] getInitializationVector() {
            return hexStringToByteArray("247D8AC4DDB1AA739DC593821D0BC432");
        }

        private byte[] getInitializationVectorCFB() {
            return hexStringToByteArray("247D8AC4DDB1AA739DC593821D0BC432");
        }

        private byte[] getNounce() {
            // char[] hexArray = "0123456789ABCDEF".toCharArray();
            // String nounceStr = "";
            // for (int i = 0 ; i < 16 ; i++) {
            // double random = Math.random();
            // int index = (int) (random * 16);
            // nounceStr += hexArray[index];
            // }
            // return hexStringToByteArray(nounceStr);
            return hexStringToByteArray("247D8AC4DDB1AA739DC593821D0BC432");
        }

        private byte[] mergeBytes(byte[] in1, byte[] in2) {
            byte[] out = new byte[in1.length + in2.length];
            int i = 0;
            for (int j = 0; j < in1.length; j++) {
                out[i++] = in1[j];
            }
            for (int j = 0; j < in2.length; j++) {
                out[i++] = in2[j];
            }
            return out;
        }
    }

Output

dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESkeygen 
Key generated and saved in AESkey.txt 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESencrypt 
Usage: java < classname > < mode > 
 < mode > := (ECB|CBC|OFB|CFB) 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESencrypt ecb 
Encryption done! Please check AESciphertext.txt for output!
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESdecrypt ecb 
Decryption done! Please check AESplaintext.txt for output! 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESencrypt cbc 
Encryption done! Please check AESciphertext.txt for output! 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESdecrypt cbc 
Decryption done! Please check AESplaintext.txt for output! 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESencrypt ofb 
Encryption done! Please check AESciphertext.txt for output! 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESdecrypt ofb 
Decryption done! Please check AESplaintext.txt for output! 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESencrypt cfb 
Encryption done! Please check AESciphertext.txt for output! 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$ java AESdecrypt cfb 
Decryption done! Please check AESplaintext.txt for output! 
dhanoopbhaskar@dhanoop-laptop:~/workspace/Copy/crypto/run_aes$

About Input/Output Files

AESkeygen.java - (output) AESkey.txt

AESencrypt.java - (input) AESkey.txt & AESplaintext.txt (output) AESciphertext.txt

AESdecrypt.java - (input) AESkey.txt & AESciphertext.txt (output) AESplaintext.txt