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(Java) AEAD AES 128-bit GCMDemonstrates AES encryption using the Galois/Counter Mode (GCM). GCM is an authenticated encryption mode with "additional data" (often referred to as AEAD). GCM is a cipher mode that can be applied to any symmetric encryption algorithm with a 16-byte block size, such as AES and Twofish. In GCM mode, the block encryption algorithm is transformed into a stream encryption algorithm, and therefore no padding occurs (and the PaddingScheme property does not apply). The "additional data" (known as the AAD) does not get encrypted but plays a role in the computation of the resulting "authenticated tag".
import com.chilkatsoft.*; public class ChilkatExample { static { try { System.loadLibrary("chilkat"); } catch (UnsatisfiedLinkError e) { System.err.println("Native code library failed to load.\n" + e); System.exit(1); } } public static void main(String argv[]) { // This example assumes the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. CkCrypt2 crypt = new CkCrypt2(); // Set the encryption algorithm to "AES" crypt.put_CryptAlgorithm("aes"); // Indicate that the Galois/Counter Mode (GCM) should be used: crypt.put_CipherMode("gcm"); // KeyLength may be 128, 192, 256 crypt.put_KeyLength(128); // This is the 128-bit AES secret key (in hex format) String K = "feffe9928665731c6d6a8f9467308308"; // This is the 16-byte initialization vector: String IV = "cafebabefacedbaddecaf888"; // This is the additional data to be used as input to the GCM AEAD algorithm, // but is not included in the output. It plays a role in the computation of the // resulting authenticated tag. String AAD = "feedfacedeadbeeffeedfacedeadbeefabaddad2"; // The plain-text bytes (in hex format) to be encrypted. String PT = "d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39"; // The expected cipher text (in hex format) String CT = "42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091"; // The expected authenticated tag given the above inputs. String T = "5bc94fbc3221a5db94fae95ae7121a47"; // Note: The above data are the values for test vector #4 from // the PDF document at: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf // EncodingMode specifies the encoding of the output for // encryption, and the input for decryption. // It may be "hex", "url", "base64", or "quoted-printable". crypt.put_EncodingMode("hex"); // Set the secret key and IV crypt.SetEncodedIV(IV,"hex"); crypt.SetEncodedKey(K,"hex"); // Set the additional authenticated data (AAD) boolean success = crypt.SetEncodedAad(AAD,"hex"); // For the purpose of duplicating the test vectors, we are using the EncryptEncoded method. // This method decodes the input string according to the encoding specified by the EncodingMode // property, which in this case is "hex". The decoded bytes are encrypted using the mode specified // by the CipherMode property. The resulting // encrypted bytes are encoded (again using the encoding mode specified by EncodingMode), // and the result is returned. // <b>Note:</b> The CipherMode property sets the block mode of operation (gcm, cfb, cbc, ofb, ecb, etc.) // for any of the Chilkat encryption/decryption methods (such as EncryptBytes, EncryptString, // CkEncryptFile, etc.) Just because GCM mode is demonstrated with EncryptEncoded/DecryptEncoded, // does not imply that GCM mode is specific to only these methods. String ctResult = crypt.encryptEncoded(PT); if (crypt.get_LastMethodSuccess() != true) { System.out.println(crypt.lastErrorText()); return; } // Examine the result. It should be the same (case insensitive) as our expected result: System.out.println("computed result: " + ctResult); System.out.println("expected result: " + CT); // Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag: String tResult = crypt.getEncodedAuthTag("hex"); System.out.println("computed authTag: " + tResult); System.out.println("expected authTag: " + T); // ------------------------------------------------------------------------------------- // Now let's GCM decrypt... // ------------------------------------------------------------------------------------- // Before GCM decrypting, we must set the authenticated tag to the value that is expected. // The decryption will fail if the resulting authenticated tag is not equal (case insensitive) to // the expected result. // Note: The return value of SetEncodedAuthTag indicates whether the string passed was a valid // representation of the encoding specified in the 2nd arg. success = crypt.SetEncodedAuthTag(T,"hex"); // All of our properties (IV, secret key, cipher mode, and AAD) are already set from the code above... // So let's decrypt CT to and check to see if we get PT. String ptResult = crypt.decryptEncoded(CT); if (crypt.get_LastMethodSuccess() != true) { // Failed. The resultant authenticated tag did not equal the expected authentication tag. System.out.println(crypt.lastErrorText()); return; } // Examine the decrypted result. It should be the same as our expected plaintext (case insensitive) System.out.println("plaintext decrypted: " + ptResult); System.out.println("plaintext expected: " + PT); // Let's intentionally set the expected authenticated tag to an incorrect value. // The decrypt operation should fail: String tInvalid = "ffaabbbc3221a5db94fae95ae7121a47"; success = crypt.SetEncodedAuthTag(tInvalid,"hex"); ptResult = crypt.decryptEncoded(CT); if (crypt.get_LastMethodSuccess() != true) { // Failed. The resultant authenticated tag did not equal the expected authentication tag. System.out.println(crypt.lastErrorText()); } } } |
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