DataFlex

Example: Crypt2.RandomizeIV method

Demonstrates using a random initialization vector for AES GCM encryption. DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoCrypt
    String K
    String sAAD
    String sPT
    String sIV
    String sCipherText
    String sAuthTag
    Handle hoBdEncrypted
    String sConcatenatedGcmOutput
    Handle hoDecrypt
    Handle hoBdFromEncryptor
    Integer iSz
    String sExtractedIV
    String sExtractedCipherText
    String sExpectedAuthTag
    String sDecryptedText
    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 ComCryptAlgorithm Of hoCrypt To "aes"
    Set ComCipherMode Of hoCrypt To "gcm"
    Set ComKeyLength Of hoCrypt To 256

    Move "000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F" To K
    Move "feedfacedeadbeeffeedfacedeadbeefabaddad2" To sAAD
    Move "This is the text to be AES-GCM encrypted." To sPT

    // Generate a random IV.
    Send ComRandomizeIV To hoCrypt
    Get ComGetEncodedIV Of hoCrypt "hex" To sIV

    Send ComSetEncodedKey To hoCrypt K "hex"

    Get ComSetEncodedAad Of hoCrypt sAAD "hex" To iSuccess

    // Return the encrypted bytes as base64
    Set ComEncodingMode Of hoCrypt To "base64"
    Set ComCharset Of hoCrypt To "utf-8"
    Get ComEncryptStringENC Of hoCrypt sPT To sCipherText
    Get ComLastMethodSuccess Of hoCrypt To bTemp1
    If (bTemp1 <> True) Begin
        Get ComLastErrorText Of hoCrypt To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Get the GCM authenticated tag computed when encrypting.
    Get ComGetEncodedAuthTag Of hoCrypt "base64" To sAuthTag

    Showln "Cipher Text: " sCipherText
    Showln "Auth Tag: " sAuthTag

    // Let's send the IV, CipherText, and AuthTag to the decrypting party.
    // We'll send them concatenated like this: [IV || Ciphertext || AuthTag]
    // In base64 format.
    Get Create (RefClass(cComChilkatBinData)) To hoBdEncrypted
    If (Not(IsComObjectCreated(hoBdEncrypted))) Begin
        Send CreateComObject of hoBdEncrypted
    End
    Get ComAppendEncoded Of hoBdEncrypted sIV "hex" To iSuccess
    Get ComAppendEncoded Of hoBdEncrypted sCipherText "base64" To iSuccess
    Get ComAppendEncoded Of hoBdEncrypted sAuthTag "base64" To iSuccess

    Get ComGetEncoded Of hoBdEncrypted "base64" To sConcatenatedGcmOutput
    Showln "Concatenated GCM Output: " sConcatenatedGcmOutput

    // Sample output so far:

    // -------------------------------------------------------------------------------------
    // Now let's GCM decrypt...
    // -------------------------------------------------------------------------------------

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

    // The values shared and agreed upon by both sides beforehand are: algorithm, cipher mode, secret key, and AAD.
    // Sometimes the IV can be a value already known and agreed upon, but in this case the encryptor sends the IV to the decryptor.
    Set ComCryptAlgorithm Of hoDecrypt To "aes"
    Set ComCipherMode Of hoDecrypt To "gcm"
    Set ComKeyLength Of hoDecrypt To 256
    Send ComSetEncodedKey To hoDecrypt K "hex"
    Get ComSetEncodedAad Of hoDecrypt sAAD "hex" To iSuccess

    Get Create (RefClass(cComChilkatBinData)) To hoBdFromEncryptor
    If (Not(IsComObjectCreated(hoBdFromEncryptor))) Begin
        Send CreateComObject of hoBdFromEncryptor
    End
    Get ComAppendEncoded Of hoBdFromEncryptor sConcatenatedGcmOutput "base64" To iSuccess

    Get ComNumBytes Of hoBdFromEncryptor To iSz

    // Extract the parts.
    Get ComGetEncodedChunk Of hoBdFromEncryptor 0 16 "hex" To sExtractedIV
    Get ComGetEncodedChunk Of hoBdFromEncryptor 16 (iSz - 32) "base64" To sExtractedCipherText
    Get ComGetEncodedChunk Of hoBdFromEncryptor (iSz - 16) 16 "base64" To sExpectedAuthTag

    // 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 to the expected result.
    Get ComSetEncodedAuthTag Of hoDecrypt sExpectedAuthTag "base64" To iSuccess

    // Also set the IV.
    Send ComSetEncodedIV To hoDecrypt sExtractedIV "hex"

    // Decrypt..
    Set ComEncodingMode Of hoDecrypt To "base64"
    Set ComCharset Of hoDecrypt To "utf-8"
    Get ComDecryptStringENC Of hoDecrypt sExtractedCipherText To sDecryptedText
    Get ComLastMethodSuccess Of hoDecrypt To bTemp1
    If (bTemp1 <> True) Begin
        // Failed.  The resultant authenticated tag did not equal the expected authentication tag.
        Get ComLastErrorText Of hoDecrypt To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Decrypted: " sDecryptedText


End_Procedure