(Visual FoxPro) 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

LOCAL loRsa
LOCAL lnSuccess
LOCAL lcPubKeyXml
LOCAL loPubKey
LOCAL lcPrivKeyXml
LOCAL loPrivKey
LOCAL loCrypt
LOCAL lcRandomKey
LOCAL loRsa2
LOCAL loPubKey2
LOCAL lnBUsePrivateKey
LOCAL lcEncryptedAesKey
LOCAL loRsa3
LOCAL loPrivKey2
LOCAL lcDecryptedAesKey
LOCAL loCrypt2

* 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.

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rsa')
loRsa = CreateObject('Chilkat.Rsa')

* Generate a 1024-bit key. 
lnSuccess = loRsa.GenerateKey(1024)
IF (lnSuccess <> 1) THEN
    ? loRsa.LastErrorText
    RELEASE loRsa
    CANCEL
ENDIF

* Keys are exported in XML format:
lcPubKeyXml = loRsa.ExportPublicKey()

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PublicKey')
loPubKey = CreateObject('Chilkat.PublicKey')
lnSuccess = loPubKey.LoadFromString(lcPubKeyXml)
* For brevity, we are not checking the return value...
lnSuccess = loPubKey.SavePemFile(0,"qa_temp/pubKey.pem")

lcPrivKeyXml = loRsa.ExportPrivateKey()

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PrivateKey')
loPrivKey = CreateObject('Chilkat.PrivateKey')
lnSuccess = loPrivKey.LoadXml(lcPrivKeyXml)
lnSuccess = loPrivKey.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.

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt = CreateObject('Chilkat.Crypt2')

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

* Generate random bytes and return the random bytes
* in a hex string:
loCrypt.EncodingMode = "hex"
lcRandomKey = loCrypt.GenRandomBytesENC(32)
? "AES key = " + lcRandomKey

* Set the key.
loCrypt.SetEncodedKey(lcRandomKey,"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.
loCrypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex")

* AES Encrypt the file (the file may be any size because it will
* stream the file in/out.
lnSuccess = loCrypt.CkEncryptFile("qa_data/hamlet.xml","qa_temp/aesEncrypted.dat")
IF (lnSuccess <> 1) THEN
    ? loCrypt.LastErrorText
    RELEASE loRsa
    RELEASE loPubKey
    RELEASE loPrivKey
    RELEASE loCrypt
    CANCEL
ENDIF

* ------------------
* 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..
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rsa')
loRsa2 = CreateObject('Chilkat.Rsa')
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PublicKey')
loPubKey2 = CreateObject('Chilkat.PublicKey')

* For brevity, don't check the success..  
lnSuccess = loPubKey2.LoadFromFile("qa_temp/pubKey.pem")
lcPubKeyXml = loPubKey2.GetXml()
lnSuccess = loRsa2.ImportPublicKey(lcPubKeyXml)

* RSA encrypt the AES key and return it as a base64 encoded string.
loRsa2.EncodingMode = "base64"
lnBUsePrivateKey = 0
lcEncryptedAesKey = loRsa2.EncryptStringENC(lcRandomKey,lnBUsePrivateKey)

* 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.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rsa')
loRsa3 = CreateObject('Chilkat.Rsa')
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PrivateKey')
loPrivKey2 = CreateObject('Chilkat.PrivateKey')

lnSuccess = loPrivKey2.LoadPemFile("qa_temp/privKey.pem")
lcPrivKeyXml = loPrivKey2.GetXml()
lnSuccess = loRsa3.ImportPrivateKey(lcPrivKeyXml)

* The encrypted AES key is encoded using base64, so set
* our EncodingMode to "base64".
loRsa3.EncodingMode = "base64"

lnBUsePrivateKey = 1
lcDecryptedAesKey = loRsa3.DecryptStringENC(lcEncryptedAesKey,lnBUsePrivateKey)
? "decryptedAesKey = " + lcDecryptedAesKey

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt2 = CreateObject('Chilkat.Crypt2')

loCrypt2.CryptAlgorithm = "aes"
loCrypt2.CipherMode = "cbc"
loCrypt2.KeyLength = 256

* Set the key.
loCrypt2.SetEncodedKey(lcDecryptedAesKey,"hex")

* Set the IV 
loCrypt2.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex")

* AES Decrypt the file (the file may be any size because it will
* stream the file in/out.
lnSuccess = loCrypt2.CkDecryptFile("qa_temp/aesEncrypted.dat","qa_temp/decrypted.xml")
IF (lnSuccess <> 1) THEN
    ? loCrypt2.LastErrorText
    RELEASE loRsa
    RELEASE loPubKey
    RELEASE loPrivKey
    RELEASE loCrypt
    RELEASE loRsa2
    RELEASE loPubKey2
    RELEASE loRsa3
    RELEASE loPrivKey2
    RELEASE loCrypt2
    CANCEL
ENDIF

RELEASE loRsa
RELEASE loPubKey
RELEASE loPrivKey
RELEASE loCrypt
RELEASE loRsa2
RELEASE loPubKey2
RELEASE loRsa3
RELEASE loPrivKey2
RELEASE loCrypt2