DataFlex

AEAD AES 128-bit GCM

See more Encryption Examples

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". DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoCrypt
    String K
    String sIV
    String sAAD
    String sPT
    String sCT
    String T
    String sCtResult
    String sTResult
    String sPtResult
    String sTInvalid
    String sTemp1
    Boolean bTemp1

    Move False To iSuccess

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    Get Create (RefClass(cComChilkatCrypt2)) To hoCrypt
    If (Not(IsComObjectCreated(hoCrypt))) Begin
        Send CreateComObject of hoCrypt
    End

    // Set the encryption algorithm to "AES"	
    Set ComCryptAlgorithm Of hoCrypt To "aes"

    // Indicate that the Galois/Counter Mode (GCM) should be used:
    Set ComCipherMode Of hoCrypt To "gcm"

    // KeyLength may be 128, 192, 256
    Set ComKeyLength Of hoCrypt To 128

    // This is the 128-bit AES secret key (in hex format)
    Move "feffe9928665731c6d6a8f9467308308" To K

    // This is the 16-byte initialization vector:
    Move "cafebabefacedbaddecaf888" To sIV

    // 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.
    Move "feedfacedeadbeeffeedfacedeadbeefabaddad2" To sAAD

    // The plain-text bytes (in hex format) to be encrypted.
    Move "d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39" To sPT

    // The expected cipher text (in hex format)
    Move "42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091" To sCT

    // The expected authenticated tag given the above inputs.
    Move "5bc94fbc3221a5db94fae95ae7121a47" To T

    // 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".
    Set ComEncodingMode Of hoCrypt To "hex"

    // Set the secret key and IV
    Send ComSetEncodedIV To hoCrypt sIV "hex"
    Send ComSetEncodedKey To hoCrypt K "hex"

    // Set the additional authenticated data (AAD)
    Get ComSetEncodedAad Of hoCrypt sAAD "hex" To iSuccess

    // 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.
    Get ComEncryptEncoded Of hoCrypt sPT To sCtResult
    Get ComLastMethodSuccess Of hoCrypt To bTemp1
    If (bTemp1 <> True) Begin
        Get ComLastErrorText Of hoCrypt To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Examine the result.  It should be the same (case insensitive) as our expected result:
    Showln "computed result: " sCtResult
    Showln "expected result: " sCT

    // Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag:
    Get ComGetEncodedAuthTag Of hoCrypt "hex" To sTResult
    Showln "computed authTag: " sTResult
    Showln "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.
    Get ComSetEncodedAuthTag Of hoCrypt T "hex" To iSuccess

    // 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.
    Get ComDecryptEncoded Of hoCrypt sCT To sPtResult
    Get ComLastMethodSuccess Of hoCrypt To bTemp1
    If (bTemp1 <> True) Begin
        // Failed.  The resultant authenticated tag did not equal the expected authentication tag.
        Get ComLastErrorText Of hoCrypt To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Examine the decrypted result.  It should be the same as our expected plaintext (case insensitive)
    Showln "plaintext decrypted: " sPtResult
    Showln "plaintext expected:  " sPT

    // Let's intentionally set the expected authenticated tag to an incorrect value. 
    // The decrypt operation should fail:
    Move "ffaabbbc3221a5db94fae95ae7121a47" To sTInvalid

    Get ComSetEncodedAuthTag Of hoCrypt sTInvalid "hex" To iSuccess

    Get ComDecryptEncoded Of hoCrypt sCT To sPtResult
    Get ComLastMethodSuccess Of hoCrypt To bTemp1
    If (bTemp1 <> True) Begin
        // Failed.  The resultant authenticated tag did not equal the expected authentication tag.
        Get ComLastErrorText Of hoCrypt To sTemp1
        Showln sTemp1
    End



End_Procedure