PowerBuilder

RSA Encrypting Symmetric Secret Key

See more RSA Examples

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. PowerBuilder

integer li_rc
integer li_Success
oleobject loo_Rsa
string ls_XmlKey
oleobject loo_PubKey
oleobject loo_Crypt
string ls_SecretKey
integer li_BUsePrivateKey
string ls_EncryptedKey
string ls_EncryptedText
oleobject loo_PrivKey
string ls_DecryptedKey
oleobject loo_Crypt2
string ls_DecryptedText

li_Success = 0

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

loo_Rsa = create oleobject
li_rc = loo_Rsa.ConnectToNewObject("Chilkat.Rsa")
if li_rc < 0 then
    destroy loo_Rsa
    MessageBox("Error","Connecting to COM object failed")
    return
end if

// 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.
ls_XmlKey = loo_Rsa.SnkToXml("qa_data/rsaKeys/test.snk")
if loo_Rsa.LastMethodSuccess = 0 then
    Write-Debug loo_Rsa.LastErrorText
    destroy loo_Rsa
    return
end if

loo_PubKey = create oleobject
li_rc = loo_PubKey.ConnectToNewObject("Chilkat.PublicKey")

li_Success = loo_PubKey.LoadFromString(ls_XmlKey)
if li_Success = 0 then
    Write-Debug loo_PubKey.LastErrorText
    destroy loo_Rsa
    destroy loo_PubKey
    return
end if

loo_Rsa.UsePublicKey(loo_PubKey)

// Our message data will be encrypted using 128-bit AES
// encryption, using CBC (cipher-block chaining).
loo_Crypt = create oleobject
li_rc = loo_Crypt.ConnectToNewObject("Chilkat.Crypt2")

loo_Crypt.CryptAlgorithm = "aes"
loo_Crypt.CipherMode = "cbc"
loo_Crypt.KeyLength = 128

// Generate 128-bit (16 bytes) secret key and return as a hex string.
loo_Crypt.EncodingMode = "hex"
ls_SecretKey = loo_Crypt.GenRandomBytesENC(16)
Write-Debug "Unencrypted Key: " + ls_SecretKey

// Use the key we generated:
loo_Crypt.SetEncodedKey(ls_SecretKey,"hex")

// RSA encrypt the secret key and return as a hex string:
loo_Rsa.EncodingMode = "hex"
li_BUsePrivateKey = 0
ls_EncryptedKey = loo_Rsa.EncryptStringENC(ls_SecretKey,li_BUsePrivateKey)

// 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.
loo_Crypt.EncodingMode = "base64"
ls_EncryptedText = loo_Crypt.EncryptStringENC("Hello World!")

// Show our encrypted key and encrypted text:
Write-Debug "Encrypted Key: " + ls_EncryptedKey
Write-Debug "Encrypted Text: " + ls_EncryptedText

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

// Here's what we do at the partner end:
loo_PrivKey = create oleobject
li_rc = loo_PrivKey.ConnectToNewObject("Chilkat.PrivateKey")

li_Success = loo_PrivKey.LoadXml(ls_XmlKey)
if li_Success = 0 then
    Write-Debug loo_PrivKey.LastErrorText
    destroy loo_Rsa
    destroy loo_PubKey
    destroy loo_Crypt
    destroy loo_PrivKey
    return
end if

loo_Rsa.UsePrivateKey(loo_PrivKey)

// First, decrypt the encryptedKey:
li_BUsePrivateKey = 1
ls_DecryptedKey = loo_Rsa.DecryptStringENC(ls_EncryptedKey,li_BUsePrivateKey)
Write-Debug "Decrypted Key: " + ls_DecryptedKey

// Set our crypt object's properties and secret key:
loo_Crypt2 = create oleobject
li_rc = loo_Crypt2.ConnectToNewObject("Chilkat.Crypt2")

loo_Crypt2.CryptAlgorithm = "aes"
loo_Crypt2.CipherMode = "cbc"
loo_Crypt2.KeyLength = 128
loo_Crypt2.EncodingMode = "base64"
loo_Crypt2.SetEncodedKey(ls_DecryptedKey,"hex")

// Decrypt the message:
ls_DecryptedText = loo_Crypt2.DecryptStringENC(ls_EncryptedText)
Write-Debug "Decrypted Text: " + ls_DecryptedText


destroy loo_Rsa
destroy loo_PubKey
destroy loo_Crypt
destroy loo_PrivKey
destroy loo_Crypt2