feat(ciphers): Add PermutationCipher implementation(enhance #6697) (#6700)

* feat(ciphers): Add PermutationCipher implementation with comprehensive tests - Implement PermutationCipher class for transposition encryption/decryption - Add encrypt() and decrypt() methods with permutation key support - Include robust key validation (1-based positions, no duplicates) - Implement automatic padding for incomplete blocks using 'X' character - Add comprehensive error handling with descriptive exceptions - Create 20+ JUnit test cases covering encryption, decryption, edge cases - Support various key sizes and text processing (spaces removal, case handling) - Include detailed JavaDoc documentation with algorithm explanation Algorithm Details: - Divides plaintext into blocks based on key length - Rearranges characters within each block according to permutation positions - Supports round-trip encryption/decryption with inverse permutation - Handles edge cases: empty strings, single character keys, padding Tests include: basic functionality, different key sizes, error validation, real-world examples, and edge case handling. * Run PermutationCipherTest using Maven * refactor(PermutationCipher): clean up code by removing unnecessary whitespace and comments * fix(tests): remove unnecessary whitespace in test assertion for encryption * fix(tests): correct indentation in assertion for encryption verification --------- Co-authored-by: a <alexanderklmn@gmail.com>
2025-12-19 07:00:35 +08:00 · 2025-10-08 12:12:58 +05:30
parent 74647e3f63
commit c06dc292fe
2 changed files with 517 additions and 0 deletions
--- a/src/test/java/com/thealgorithms/ciphers/PermutationCipherTest.java
+++ b/src/test/java/com/thealgorithms/ciphers/PermutationCipherTest.java
@@ -0,0 +1,323 @@
+package com.thealgorithms.ciphers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class PermutationCipherTest {
+
+    private final PermutationCipher cipher = new PermutationCipher();
+
+    @Test
+    void testBasicEncryption() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = {3, 1, 2}; // Move 3rd position to 1st, 1st to 2nd, 2nd to 3rd
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+
+        // then
+        // "HELLO" becomes "HEL" + "LOX" (padded)
+        // "HEL" with key {3,1,2} becomes "LHE" (L=3rd, H=1st, E=2nd)
+        // "LOX" with key {3,1,2} becomes "XLO" (X=3rd, L=1st, O=2nd)
+        assertEquals("LHEXLO", encrypted);
+    }
+
+    @Test
+    void testBasicDecryption() {
+        // given
+        String ciphertext = "LHEXLO";
+        int[] key = {3, 1, 2};
+
+        // when
+        String decrypted = cipher.decrypt(ciphertext, key);
+
+        // then
+        assertEquals("HELLO", decrypted);
+    }
+
+    @Test
+    void testEncryptDecryptRoundTrip() {
+        // given
+        String plaintext = "THIS IS A TEST MESSAGE";
+        int[] key = {4, 2, 1, 3};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("THISISATESTMESSAGE", decrypted); // Spaces are removed during encryption
+    }
+
+    @Test
+    void testSingleCharacterKey() {
+        // given
+        String plaintext = "ABCDEF";
+        int[] key = {1}; // Identity permutation
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("ABCDEF", encrypted); // Should remain unchanged
+        assertEquals("ABCDEF", decrypted);
+    }
+
+    @Test
+    void testLargerKey() {
+        // given
+        String plaintext = "PERMUTATION";
+        int[] key = {5, 3, 1, 4, 2}; // 5-character permutation
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("PERMUTATION", decrypted);
+    }
+
+    @Test
+    void testExactBlockSize() {
+        // given
+        String plaintext = "ABCDEF"; // Length 6, divisible by key length 3
+        int[] key = {2, 3, 1};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("ABCDEF", decrypted);
+    }
+
+    @Test
+    void testEmptyString() {
+        // given
+        String plaintext = "";
+        int[] key = {2, 1, 3};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("", encrypted);
+        assertEquals("", decrypted);
+    }
+
+    @Test
+    void testNullString() {
+        // given
+        String plaintext = null;
+        int[] key = {2, 1, 3};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals(null, encrypted);
+        assertEquals(null, decrypted);
+    }
+
+    @Test
+    void testStringWithSpaces() {
+        // given
+        String plaintext = "A B C D E F";
+        int[] key = {2, 1};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("ABCDEF", decrypted); // Spaces should be removed
+    }
+
+    @Test
+    void testLowercaseConversion() {
+        // given
+        String plaintext = "hello world";
+        int[] key = {3, 1, 2};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("HELLOWORLD", decrypted); // Should be converted to uppercase
+    }
+
+    @Test
+    void testInvalidKeyNull() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = null;
+
+        // when & then
+        assertThrows(IllegalArgumentException.class, () -> cipher.encrypt(plaintext, key));
+        assertThrows(IllegalArgumentException.class, () -> cipher.decrypt(plaintext, key));
+    }
+
+    @Test
+    void testInvalidKeyEmpty() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = {};
+
+        // when & then
+        assertThrows(IllegalArgumentException.class, () -> cipher.encrypt(plaintext, key));
+        assertThrows(IllegalArgumentException.class, () -> cipher.decrypt(plaintext, key));
+    }
+
+    @Test
+    void testInvalidKeyOutOfRange() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = {1, 2, 4}; // 4 is out of range for key length 3
+
+        // when & then
+        assertThrows(IllegalArgumentException.class, () -> cipher.encrypt(plaintext, key));
+        assertThrows(IllegalArgumentException.class, () -> cipher.decrypt(plaintext, key));
+    }
+
+    @Test
+    void testInvalidKeyZero() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = {0, 1, 2}; // 0 is invalid (should be 1-based)
+
+        // when & then
+        assertThrows(IllegalArgumentException.class, () -> cipher.encrypt(plaintext, key));
+        assertThrows(IllegalArgumentException.class, () -> cipher.decrypt(plaintext, key));
+    }
+
+    @Test
+    void testInvalidKeyDuplicate() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = {1, 2, 2}; // Duplicate position
+
+        // when & then
+        assertThrows(IllegalArgumentException.class, () -> cipher.encrypt(plaintext, key));
+        assertThrows(IllegalArgumentException.class, () -> cipher.decrypt(plaintext, key));
+    }
+
+    @Test
+    void testInvalidKeyMissingPosition() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = {1, 3}; // Missing position 2
+
+        // when & then
+        assertThrows(IllegalArgumentException.class, () -> cipher.encrypt(plaintext, key));
+        assertThrows(IllegalArgumentException.class, () -> cipher.decrypt(plaintext, key));
+    }
+
+    @Test
+    void testReverseKey() {
+        // given
+        String plaintext = "ABCD";
+        int[] key = {4, 3, 2, 1}; // Reverse order
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("DCBA", encrypted); // Should be reversed
+        assertEquals("ABCD", decrypted);
+    }
+
+    @Test
+    void testSpecificExampleFromDescription() {
+        // given
+        String plaintext = "HELLO";
+        int[] key = {3, 1, 2};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+
+        // then
+        // Block 1: "HEL" -> positions {3,1,2} -> "LHE"
+        // Block 2: "LOX" -> positions {3,1,2} -> "XLO"
+        assertEquals("LHEXLO", encrypted);
+        // Verify decryption
+        String decrypted = cipher.decrypt(encrypted, key);
+        assertEquals("HELLO", decrypted);
+    }
+
+    @Test
+    void testPaddingCharacterGetter() {
+        // when
+        char paddingChar = cipher.getPaddingChar();
+
+        // then
+        assertEquals('X', paddingChar);
+    }
+
+    @Test
+    void testLongText() {
+        // given
+        String plaintext = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG";
+        int[] key = {4, 1, 3, 2};
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("THEQUICKBROWNFOXJUMPSOVERTHELAZYDOG", decrypted);
+    }
+
+    @Test
+    void testIdentityPermutation() {
+        // given
+        String plaintext = "IDENTITY";
+        int[] key = {1, 2, 3, 4}; // Identity permutation
+
+        // when
+        String encrypted = cipher.encrypt(plaintext, key);
+        String decrypted = cipher.decrypt(encrypted, key);
+
+        // then
+        assertEquals("IDENTITY", encrypted); // Should remain unchanged
+        assertEquals("IDENTITY", decrypted);
+    }
+
+    @Test
+    void testEmptyStringRemovePadding() {
+        // given - Test to cover line 178 (empty string case in removePadding)
+        String ciphertext = "";
+        int[] key = {2, 1, 3};
+
+        // when
+        String decrypted = cipher.decrypt(ciphertext, key);
+
+        // then
+        assertEquals("", decrypted); // Should return empty string directly
+    }
+
+    @Test
+    void testBlockShorterThanKey() {
+        // given - Test to cover line 139 (block length != key length case)
+        // This is a defensive case where permuteBlock might receive a block shorter than key
+        // We can test this by manually creating a scenario with malformed ciphertext
+        String malformedCiphertext = "AB"; // Length 2, but key length is 3
+        int[] key = {3, 1, 2}; // Key length is 3
+
+        // when - This should trigger the padding logic in permuteBlock during decryption
+        String decrypted = cipher.decrypt(malformedCiphertext, key);
+
+        // then - The method should handle the short block gracefully
+        // "AB" gets padded to "ABX", then permuted with inverse key {2,3,1}
+        // inverse key {2,3,1} means: pos 2→1st, pos 3→2nd, pos 1→3rd = "BXA"
+        // Padding removal only removes trailing X's, so "BXA" remains as is
+        assertEquals("BXA", decrypted);
+    }
+}