(DataFlex) RSA Encrypting Symmetric Secret Key

The RSA encryption algorithm is computationally expensive. It is not the best choice for encrypting large amounts of data. Symmetric encryption algorithms such as AES (i.e. Rijndael) or Blowfish are much more efficient. A typical application scenario is that you want to send encrypted messages to a partner, but you don't want to send the symmetric key unprotected. A solution is to generate a public/private RSA key pair and provide your partner with the public key (in advance). You may then encrypt the symmetric algorithm's key using the RSA private key. Next, encrypt the message using the symmetric algorithm, and send your partner both the encrypted key and encrypted message. Your partner decrypts by first RSA decrypting the key, and then uses the decrypted symmetric key to decrypt the message content.

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoRsa
    String sXmlKey
    Variant vPubKey
    Handle hoPubKey
    Handle hoCrypt
    String sSecretKey
    Boolean iBUsePrivateKey
    String sEncryptedKey
    String sEncryptedText
    Variant vPrivKey
    Handle hoPrivKey
    String sDecryptedKey
2    Handle hoCrypt2
    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(cComChilkatRsa)) To hoRsa
    If (Not(IsComObjectCreated(hoRsa))) Begin
        Send CreateComObject of hoRsa
    End

    // Load a public/private key pair from a .snk key file.
    // Assume you have already provided your partner with 
    // the public key part of the key pair.
    Get ComSnkToXml Of hoRsa "qa_data/rsaKeys/test.snk" To sXmlKey
    Get ComLastMethodSuccess Of hoRsa To bTemp1
    If (bTemp1 = False) Begin
        Get ComLastErrorText Of hoRsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get Create (RefClass(cComChilkatPublicKey)) To hoPubKey
    If (Not(IsComObjectCreated(hoPubKey))) Begin
        Send CreateComObject of hoPubKey
    End
    Get ComLoadFromString Of hoPubKey sXmlKey To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoPubKey To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get pvComObject of hoPubKey to vPubKey
    Get ComUsePublicKey Of hoRsa vPubKey To iSuccess

    // Our message data will be encrypted using 128-bit AES
    // encryption, using CBC (cipher-block chaining).
    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 "cbc"
    Set ComKeyLength Of hoCrypt To 128

    // Generate 128-bit (16 bytes) secret key and return as a hex string.
    Set ComEncodingMode Of hoCrypt To "hex"
    Get ComGenRandomBytesENC Of hoCrypt 16 To sSecretKey
    Showln "Unencrypted Key: " sSecretKey

    // Use the key we generated:
    Send ComSetEncodedKey To hoCrypt sSecretKey "hex"

    // RSA encrypt the secret key and return as a hex string:
    Set ComEncodingMode Of hoRsa To "hex"
    Move False To iBUsePrivateKey
    Get ComEncryptStringENC Of hoRsa sSecretKey iBUsePrivateKey To sEncryptedKey

    // Symmetric encrypt a message.  For this example the message
    // is very short, but typically this is where a large amount
    // of data may be encrypted.
    Set ComEncodingMode Of hoCrypt To "base64"
    Get ComEncryptStringENC Of hoCrypt "Hello World!" To sEncryptedText

    // Show our encrypted key and encrypted text:
    Showln "Encrypted Key: " sEncryptedKey
    Showln "Encrypted Text: " sEncryptedText

    // Assume we sent these strings to our partner...

    // Here's what we do at the partner end:
    Get Create (RefClass(cComChilkatPrivateKey)) To hoPrivKey
    If (Not(IsComObjectCreated(hoPrivKey))) Begin
        Send CreateComObject of hoPrivKey
    End
    Get ComLoadXml Of hoPrivKey sXmlKey To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoPrivKey To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get pvComObject of hoPrivKey to vPrivKey
    Get ComUsePrivateKey Of hoRsa vPrivKey To iSuccess

    // First, decrypt the encryptedKey:
    Move True To iBUsePrivateKey
    Get ComDecryptStringENC Of hoRsa sEncryptedKey iBUsePrivateKey To sDecryptedKey
    Showln "Decrypted Key: " sDecryptedKey

    // Set our crypt object's properties and secret key:
    Get Create (RefClass(cComChilkatCrypt2)) To hoCrypt2
    If (Not(IsComObjectCreated(hoCrypt2))) Begin
        Send CreateComObject of hoCrypt2
    End
    Set ComCryptAlgorithm Of hoCrypt2 To "aes"
    Set ComCipherMode Of hoCrypt2 To "cbc"
    Set ComKeyLength Of hoCrypt2 To 128
    Set ComEncodingMode Of hoCrypt2 To "base64"
    Send ComSetEncodedKey To hoCrypt2 sDecryptedKey "hex"

    // Decrypt the message:
    Get ComDecryptStringENC Of hoCrypt2 sEncryptedText To sDecryptedText
    Showln "Decrypted Text: " sDecryptedText


End_Procedure