(Excel) RSA Encrypt and Decrypt Credit Card Numbers

Excel sample code to RSA public-key encrypt and decrypt credit card numbers. The RSA key is loaded from an unencrypted PKCS8 file. Chilkat provides many ways of setting the key -- loading from both encrypted and unencrypted PEM, PKCS8, DER, PVK, etc. Keys may be loaded from files or in-memory representations. (The RSA component also provides the ability to generate RSA keys.)

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

Dim rsa As Chilkat.Rsa
Set rsa = Chilkat.NewRsa

Dim key As Chilkat.PrivateKey
Set key = Chilkat.NewPrivateKey

' Load an RSA private key from a PKCS8 file:

success = key.LoadPkcs8File("rsaPrivateKey.p8")
If (success <> True) Then
    Debug.Print key.LastErrorText
    Exit Sub
End If

' Get the key as XML:

keyXml = key.GetXml()

' We'll encrypt with the public key and decrypt with the private
' key.  (It's also possible to do the reverse.)
' Note: An RSA private key is composed of different parts internally: modulus, exponent, P, Q, etc.
' An RSA public-key is a sub-set of the private key.
' Therefore, when you have a private key, you really have
' both public and private keys.
success = rsa.ImportPublicKey(keyXml)
If (success <> True) Then
    Debug.Print rsa.LastErrorText
    Exit Sub
End If

' Encrypt a VISA credit card number:
' 1234-5678-0000-9999

ccNumber = "1234567800009999"


usePrivateKey = False
rsa.EncodingMode = "base64"

encryptedStr = rsa.EncryptStringENC(ccNumber,usePrivateKey)
Debug.Print "Encrypted:"
Debug.Print encryptedStr

' Now decrypt:
Dim rsaDecryptor As Chilkat.Rsa
Set rsaDecryptor = Chilkat.NewRsa

rsaDecryptor.EncodingMode = "base64"
success = rsaDecryptor.ImportPrivateKey(keyXml)

usePrivateKey = True

decryptedStr = rsaDecryptor.DecryptStringENC(encryptedStr,usePrivateKey)

Debug.Print "Decrypted:"
Debug.Print decryptedStr

' Important: RSA encryption should only be used to encrypt small amounts of data.
' It is typically used for encrypting symmetric encryption
' keys such that a symmetric encryption algorithm, such as 
' AES is then used to encrypt/decrypt bulk data