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(Java) AEAD AES 128-bit GCM

Demonstrates 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".

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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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