(PowerBuilder) RSA Encrypt/Decrypt AES Key

Demonstrates how to use RSA to protect a key for AES encryption. It can be used in this scenario: You will provide your RSA public key to any number of counterparts. Your counterpart will generate an AES key, encrypt data (or a file) using it, then encrypt the AES key using your RSA public key. Your counterpart sends you both the encrypted data and the encrypted key. Since you are the only one with access to the RSA private key, only you can decrypt the AES key. You decrypt the key, then decrypt the data using the AES key.

This example will show the entire process. (1) Generate an RSA key and save both private and public parts to PEM files. (2) Encrypt a file using a randomly generated AES encryption key. (3) RSA encrypt the AES key. (4) RSA decrypt the AES key. (5) Use it to AES decrypt the file or data.

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

integer li_rc
oleobject loo_Rsa
integer li_Success
string ls_PubKeyXml
oleobject loo_PubKey
string ls_PrivKeyXml
oleobject loo_PrivKey
oleobject loo_Crypt
string ls_RandomKey
oleobject loo_Rsa2
oleobject loo_PubKey2
integer li_BUsePrivateKey
string ls_EncryptedAesKey
oleobject loo_Rsa3
oleobject loo_PrivKey2
string ls_DecryptedAesKey
oleobject loo_Crypt2

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

// ------------------
// Step 1.  Generate an RSA key and save to PEM files.

loo_Rsa = create oleobject
// Use "Chilkat_9_5_0.Rsa" for versions of Chilkat < 10.0.0
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

// Generate a 1024-bit key. 
li_Success = loo_Rsa.GenerateKey(1024)
if li_Success <> 1 then
    Write-Debug loo_Rsa.LastErrorText
    destroy loo_Rsa
    return
end if

// Keys are exported in XML format:
ls_PubKeyXml = loo_Rsa.ExportPublicKey()

loo_PubKey = create oleobject
// Use "Chilkat_9_5_0.PublicKey" for versions of Chilkat < 10.0.0
li_rc = loo_PubKey.ConnectToNewObject("Chilkat.PublicKey")

li_Success = loo_PubKey.LoadFromString(ls_PubKeyXml)
// For brevity, we are not checking the return value...
li_Success = loo_PubKey.SavePemFile(0,"qa_temp/pubKey.pem")

ls_PrivKeyXml = loo_Rsa.ExportPrivateKey()

loo_PrivKey = create oleobject
// Use "Chilkat_9_5_0.PrivateKey" for versions of Chilkat < 10.0.0
li_rc = loo_PrivKey.ConnectToNewObject("Chilkat.PrivateKey")

li_Success = loo_PrivKey.LoadXml(ls_PrivKeyXml)
li_Success = loo_PrivKey.SavePemFile("qa_temp/privKey.pem")

// Other methods exist for saving the private key in PKCS8 format,
// both encrypted and un-encrypted..

// ------------------
// Step 2.   This is the code your counterpart will run to 
// AES encrypt a file.  It generates a random AES key
// to use for the encryption.

loo_Crypt = create oleobject
// Use "Chilkat_9_5_0.Crypt2" for versions of Chilkat < 10.0.0
li_rc = loo_Crypt.ConnectToNewObject("Chilkat.Crypt2")

loo_Crypt.CryptAlgorithm = "aes"
loo_Crypt.CipherMode = "cbc"
loo_Crypt.KeyLength = 256

// Generate random bytes and return the random bytes
// in a hex string:
loo_Crypt.EncodingMode = "hex"
ls_RandomKey = loo_Crypt.GenRandomBytesENC(32)
Write-Debug "AES key = " + ls_RandomKey

// Set the key.
loo_Crypt.SetEncodedKey(ls_RandomKey,"hex")

// Set the IV to a known value that will be used on both sides.
// (If desired, you could generate a random IV and protect it in the same
// way as the key...)
// The length of the IV for AES is always 16 bytes, regardless of the key size.
loo_Crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex")

// AES Encrypt the file (the file may be any size because it will
// stream the file in/out.
li_Success = loo_Crypt.CkEncryptFile("qa_data/hamlet.xml","qa_temp/aesEncrypted.dat")
if li_Success <> 1 then
    Write-Debug loo_Crypt.LastErrorText
    destroy loo_Rsa
    destroy loo_PubKey
    destroy loo_PrivKey
    destroy loo_Crypt
    return
end if

// ------------------
// Step 3.
// ------------------
// RSA encrypt the AES key.
// We'll pretend  your counter part has the public-key PEM file and needs
// to load it.  Therefore, we'll start with a new RSA object and load
// the public key from the PEM..
loo_Rsa2 = create oleobject
// Use "Chilkat_9_5_0.Rsa" for versions of Chilkat < 10.0.0
li_rc = loo_Rsa2.ConnectToNewObject("Chilkat.Rsa")

loo_PubKey2 = create oleobject
// Use "Chilkat_9_5_0.PublicKey" for versions of Chilkat < 10.0.0
li_rc = loo_PubKey2.ConnectToNewObject("Chilkat.PublicKey")

// For brevity, don't check the success..  
li_Success = loo_PubKey2.LoadFromFile("qa_temp/pubKey.pem")
ls_PubKeyXml = loo_PubKey2.GetXml()
li_Success = loo_Rsa2.ImportPublicKey(ls_PubKeyXml)

// RSA encrypt the AES key and return it as a base64 encoded string.
loo_Rsa2.EncodingMode = "base64"
li_BUsePrivateKey = 0
ls_EncryptedAesKey = loo_Rsa2.EncryptStringENC(ls_RandomKey,li_BUsePrivateKey)

// At this point, your counterpart sends you the encryptedAesKey,
// and the encrypted file.

// ------------------
// Step 4 - RSA decrypt the AES key.
// ------------------

// Start with a new RSA object and load the private key from the PEM.
loo_Rsa3 = create oleobject
// Use "Chilkat_9_5_0.Rsa" for versions of Chilkat < 10.0.0
li_rc = loo_Rsa3.ConnectToNewObject("Chilkat.Rsa")

loo_PrivKey2 = create oleobject
// Use "Chilkat_9_5_0.PrivateKey" for versions of Chilkat < 10.0.0
li_rc = loo_PrivKey2.ConnectToNewObject("Chilkat.PrivateKey")

li_Success = loo_PrivKey2.LoadPemFile("qa_temp/privKey.pem")
ls_PrivKeyXml = loo_PrivKey2.GetXml()
li_Success = loo_Rsa3.ImportPrivateKey(ls_PrivKeyXml)

// The encrypted AES key is encoded using base64, so set
// our EncodingMode to "base64".
loo_Rsa3.EncodingMode = "base64"

li_BUsePrivateKey = 1
ls_DecryptedAesKey = loo_Rsa3.DecryptStringENC(ls_EncryptedAesKey,li_BUsePrivateKey)
Write-Debug "decryptedAesKey = " + ls_DecryptedAesKey

// ------------------
// Step 5 - AES decrypt the file.
// ------------------

loo_Crypt2 = create oleobject
// Use "Chilkat_9_5_0.Crypt2" for versions of Chilkat < 10.0.0
li_rc = loo_Crypt2.ConnectToNewObject("Chilkat.Crypt2")

loo_Crypt2.CryptAlgorithm = "aes"
loo_Crypt2.CipherMode = "cbc"
loo_Crypt2.KeyLength = 256

// Set the key.
loo_Crypt2.SetEncodedKey(ls_DecryptedAesKey,"hex")

// Set the IV 
loo_Crypt2.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex")

// AES Decrypt the file (the file may be any size because it will
// stream the file in/out.
li_Success = loo_Crypt2.CkDecryptFile("qa_temp/aesEncrypted.dat","qa_temp/decrypted.xml")
if li_Success <> 1 then
    Write-Debug loo_Crypt2.LastErrorText
    destroy loo_Rsa
    destroy loo_PubKey
    destroy loo_PrivKey
    destroy loo_Crypt
    destroy loo_Rsa2
    destroy loo_PubKey2
    destroy loo_Rsa3
    destroy loo_PrivKey2
    destroy loo_Crypt2
    return
end if



destroy loo_Rsa
destroy loo_PubKey
destroy loo_PrivKey
destroy loo_Crypt
destroy loo_Rsa2
destroy loo_PubKey2
destroy loo_Rsa3
destroy loo_PrivKey2
destroy loo_Crypt2