**Java:**

public class DES {

private static final int[] IP = { 58, 50, 42, 34, 26, 18, 10, 2,

60, 52, 44, 36, 28, 20, 12, 4,

62, 54, 46, 38, 30, 22, 14, 6,

64, 56, 48, 40, 32, 24, 16, 8,

57, 49, 41, 33, 25, 17, 9, 1,

59, 51, 43, 35, 27, 19, 11, 3,

61, 53, 45, 37, 29, 21, 13, 5,

63, 55, 47, 39, 31, 23, 15, 7 };

private static final int[] E = { 32, 1, 2, 3, 4, 5,

4, 5, 6, 7, 8, 9,

8, 9, 10, 11, 12, 13,

12, 13, 14, 15, 16, 17,

16, 17, 18, 19, 20, 21,

20, 21, 22, 23, 24, 25,

24, 25, 26, 27, 28, 29,

28, 29, 30, 31, 32, 1 };

private static final int[] P = { 16, 7, 20, 21,

29, 12, 28, 17,

1, 15, 23, 26,

5, 18, 31, 10,

2, 8, 24, 14,

32, 27, 3, 9,

19, 13, 30, 6,

22, 11, 4, 25 };

private static final int[] FP = { 40, 8, 48, 16, 56, 24, 64, 32,

39, 7, 47, 15, 55, 23, 63, 31,

38, 6, 46, 14, 54, 22, 62, 30,

37, 5, 45, 13, 53, 21, 61, 29,

36, 4, 44, 12, 52, 20, 60, 28,

35, 3, 43, 11, 51, 19, 59, 27,

34, 2, 42, 10, 50, 18, 58, 26,

33, 1, 41, 9, 49, 17, 57, 25 };

private static final int[][][] S_BOXES = {

{{ 14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7 },

{ 0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8 },

{ 4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0 },

{ 15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13 }},

{{15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10},

{3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5},

{0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15},

{13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9}},

{{10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8},

{13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1},

{13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7},

{1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12}},

{{7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15},

{13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9},

{10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4},

{3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14}},

{{2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9},

{14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6},

{4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14},

{11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3}},

{{12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11},

{10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8},

{9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6},

{4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13}},

{{4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1},

{13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6},

{1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2},

{6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12}},

{{13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7},

{1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2},

{7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8},

{2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11}}

};

private static final int[] PC1 = { 57, 49, 41, 33, 25, 17, 9,

1, 58, 50, 42, 34, 26, 18,

10, 2, 59, 51, 43, 35, 27,

19, 11, 3, 60, 52, 44, 36,

63, 55, 47, 39, 31, 23, 15,

7, 62, 54, 46, 38, 30, 22,

14, 6, 61, 53, 45, 37, 29,

21, 13, 5, 28, 20, 12, 4 };

private static final int[] PC2 = { 14, 17, 11, 24, 1, 5,

3, 28, 15, 6, 21, 10,

23, 19, 12, 4, 26, 8,

16, 7, 27, 20, 13, 2,

41, 52, 31, 37, 47, 55,

30, 40, 51, 45, 33, 48,

44, 49, 39, 56, 34, 53,

46, 42, 50, 36, 29, 32 };

private static final int[] SHIFTS = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 };

// Method to perform the initial permutation on a 64-bit block

private static long initialPermutation(long block) {

return permutation(block, IP);

}

// Method to perform the final permutation on a 64-bit block

private static long finalPermutation(long block) {

return permutation(block, FP);

}

// General method to apply a permutation to a 64-bit block

private static long permutation(long block, int[] permutationTable) {

long result = 0;

for (int i = 0; i < permutationTable.length; i++) {

result <<= 1;

result |= (block >> (64 – permutationTable[i])) & 0x01;

}

return result;

}

// Method to expand a 32-bit block to 48 bits using the expansion table

private static long expansion(long halfBlock) {

return permutation(halfBlock, E);

}

// Method to apply the P permutation to a 32-bit block

private static int permuteP(int block) {

return (int) permutation(block & 0xFFFFFFFFL, P);

}

// Method to generate the 16 subkeys from the original 64-bit key

private static long[] generateSubkeys(long key) {

long[] subkeys = new long[16];

// Apply PC1 permutation

key = permutation(key, PC1);

// Split into C and D halves

int C = (int) (key >> 28) & 0x0FFFFFFF;

int D = (int) key & 0x0FFFFFFF;

// Generate each subkey

for (int round = 0; round < 16; round++) {

// Perform the left circular shift

C = ((C << SHIFTS[round]) | (C >> (28 – SHIFTS[round]))) & 0x0FFFFFFF;

D = ((D << SHIFTS[round]) | (D >> (28 – SHIFTS[round]))) & 0x0FFFFFFF;

// Combine C and D and apply PC2 permutation to get the subkey

long CD = ((long) C << 28) | D;

subkeys[round] = permutation(CD, PC2);

}

return subkeys;

}

// Method to perform the S-box substitution

private static int sBoxSubstitution(long block) {

int result = 0;

for (int i = 0; i < 8; i++) {

int sBoxInput = (int) ((block >> (42 – 6 * i)) & 0x3F);

int row = ((sBoxInput & 0x20) >> 4) | (sBoxInput & 0x01);

int col = (sBoxInput >> 1) & 0x0F;

result <<= 4;

result |= S_BOXES[i][row][col];

}

return result;

}

// The DES function that encrypts or decrypts a 64-bit block

private static long desFunction(long block, long[] subkeys, boolean isEncrypt) {

// Apply the initial permutation

block = initialPermutation(block);

// Split into L and R halves

int L = (int) (block >> 32) & 0xFFFFFFFF;

int R = (int) block & 0xFFFFFFFF;

// Perform the 16 rounds

for (int round = 0; round < 16; round++) {

int tempR = R;

// Expand R and apply the round key

R = (int) expansion(R);

if (isEncrypt) {

R ^= subkeys[round];

} else {

R ^= subkeys[15 – round];

}

// Apply the S-box substitution and P permutation

R = sBoxSubstitution(R);

R = permuteP(R);

// XOR with L and swap halves

R ^= L;

L = tempR;

}

// Combine L and R and apply the final permutation

block = ((long) R << 32) | (L & 0xFFFFFFFFL);

block = finalPermutation(block);

return block;

}

// Method to encrypt a 64-bit block

public static long encrypt(long plaintext, long key) {

long[] subkeys = generateSubkeys(key);

return desFunction(plaintext, subkeys, true);

}

// Method to decrypt a 64-bit block

public static long decrypt(long ciphertext, long key) {

long[] subkeys = generateSubkeys(key);

return desFunction(ciphertext, subkeys, false);

}

public static void main(String[] args) {

// Example usage

long plaintext = 0x0123456789ABCDEFL;

long key = 0x133457799BBCDFF1L;

System.out.printf(“Plaintext: 0x%016Xn”, plaintext);

long ciphertext = encrypt(plaintext, key);

System.out.printf(“Ciphertext: 0x%016Xn”, ciphertext);

long decrypted = decrypt(ciphertext, key);

System.out.printf(“Decrypted: 0x%016Xn”, decrypted);

// Verify if the decryption result matches the original plaintext

if (plaintext == decrypted) {

System.out.println(“Decryption successful: The decrypted text matches the original plaintext.”);

} else {

System.out.println(“Decryption failed: The decrypted text does not match the original plaintext.”);

}

}

}

**Output:**

Plaintext: 0x0123456789ABCDEF

Ciphertext: 0x02138A9B4657CEDF

Decrypted: 0x0123456789ABCDEF

Decryption successful: The decrypted text matches the original plaintext.