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Commit8d2cdb2

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feat: implement One-Time Pad cipher (#6941) (#7096)
* feat: implement One-Time Pad cipher (#6941)* style: format OneTimePadCipher with clang-format
1 parent14c0b08 commit8d2cdb2

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packagecom.thealgorithms.ciphers;
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importjava.security.SecureRandom;
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importjava.util.Objects;
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/**
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* One-Time Pad (OTP) cipher implementation.
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*
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* <p>The One-Time Pad is information-theoretically secure if:
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* <ul>
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* <li>The key is truly random.</li>
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* <li>The key length is at least as long as the plaintext.</li>
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* <li>The key is used only once and kept secret.</li>
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* </ul>
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*
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* <p>This implementation is for <b>educational purposes only</b> and should not be
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* used in production systems.
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*/
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publicfinalclassOneTimePadCipher {
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privatestaticfinalSecureRandomRANDOM =newSecureRandom();
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privateOneTimePadCipher() {
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// utility class
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}
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/**
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* Generates a random key of the given length in bytes.
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*
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* @param length the length of the key in bytes, must be non-negative
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* @return a new random key
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* @throws IllegalArgumentException if length is negative
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*/
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publicstaticbyte[]generateKey(intlength) {
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if (length <0) {
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thrownewIllegalArgumentException("length must be non-negative");
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}
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byte[]key =newbyte[length];
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RANDOM.nextBytes(key);
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returnkey;
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}
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/**
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* Encrypts the given plaintext bytes using the provided key.
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* <p>The key length must be exactly the same as the plaintext length.
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*
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* @param plaintext the plaintext bytes, must not be {@code null}
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* @param key the one-time pad key bytes, must not be {@code null}
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* @return the ciphertext bytes
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* @throws IllegalArgumentException if the key length does not match plaintext length
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* @throws NullPointerException if plaintext or key is {@code null}
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*/
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publicstaticbyte[]encrypt(byte[]plaintext,byte[]key) {
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validateInputs(plaintext,key);
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returnxor(plaintext,key);
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}
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/**
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* Decrypts the given ciphertext bytes using the provided key.
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* <p>For a One-Time Pad, decryption is identical to encryption:
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* {@code plaintext = ciphertext XOR key}.
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*
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* @param ciphertext the ciphertext bytes, must not be {@code null}
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* @param key the one-time pad key bytes, must not be {@code null}
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* @return the decrypted plaintext bytes
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* @throws IllegalArgumentException if the key length does not match ciphertext length
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* @throws NullPointerException if ciphertext or key is {@code null}
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*/
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publicstaticbyte[]decrypt(byte[]ciphertext,byte[]key) {
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validateInputs(ciphertext,key);
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returnxor(ciphertext,key);
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}
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privatestaticvoidvalidateInputs(byte[]input,byte[]key) {
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Objects.requireNonNull(input,"input must not be null");
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Objects.requireNonNull(key,"key must not be null");
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if (input.length !=key.length) {
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thrownewIllegalArgumentException("Key length must match input length");
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}
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}
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privatestaticbyte[]xor(byte[]data,byte[]key) {
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byte[]result =newbyte[data.length];
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for (inti =0;i <data.length;i++) {
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result[i] = (byte) (data[i] ^key[i]);
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}
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returnresult;
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}
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}
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packagecom.thealgorithms.ciphers;
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importstaticorg.junit.jupiter.api.Assertions.assertArrayEquals;
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importstaticorg.junit.jupiter.api.Assertions.assertEquals;
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importstaticorg.junit.jupiter.api.Assertions.assertThrows;
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importjava.nio.charset.StandardCharsets;
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importorg.junit.jupiter.api.Test;
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classOneTimePadCipherTest {
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@Test
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voidencryptAndDecryptWithRandomKeyRestoresPlaintext() {
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Stringplaintext ="The quick brown fox jumps over the lazy dog.";
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byte[]plaintextBytes =plaintext.getBytes(StandardCharsets.UTF_8);
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byte[]key =OneTimePadCipher.generateKey(plaintextBytes.length);
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byte[]ciphertext =OneTimePadCipher.encrypt(plaintextBytes,key);
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byte[]decrypted =OneTimePadCipher.decrypt(ciphertext,key);
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assertArrayEquals(plaintextBytes,decrypted);
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assertEquals(plaintext,newString(decrypted,StandardCharsets.UTF_8));
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}
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@Test
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voidgenerateKeyWithNegativeLengthThrowsException() {
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assertThrows(IllegalArgumentException.class, () ->OneTimePadCipher.generateKey(-1));
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}
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@Test
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voidencryptWithMismatchedKeyLengthThrowsException() {
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byte[]data ="hello".getBytes(StandardCharsets.UTF_8);
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byte[]shortKey =OneTimePadCipher.generateKey(2);
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assertThrows(IllegalArgumentException.class, () ->OneTimePadCipher.encrypt(data,shortKey));
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}
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@Test
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voiddecryptWithMismatchedKeyLengthThrowsException() {
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byte[]data ="hello".getBytes(StandardCharsets.UTF_8);
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byte[]key =OneTimePadCipher.generateKey(data.length);
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byte[]ciphertext =OneTimePadCipher.encrypt(data,key);
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byte[]wrongSizedKey =OneTimePadCipher.generateKey(data.length +1);
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assertThrows(IllegalArgumentException.class, () ->OneTimePadCipher.decrypt(ciphertext,wrongSizedKey));
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}
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}

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