(PureBasic) RSA Encrypt and Decrypt Credit Card Numbers

PureBasic 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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IncludeFile "CkPrivateKey.pb"
IncludeFile "CkRsa.pb"

Procedure ChilkatExample()

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

    rsa.i = CkRsa::ckCreate()
    If rsa.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    key.i = CkPrivateKey::ckCreate()
    If key.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Load an RSA private key from a file:
    success.i = CkPrivateKey::ckLoadAnyFormatFile(key,"rsaPrivateKey.key","")
    If success <> 1
        Debug CkPrivateKey::ckLastErrorText(key)
        CkRsa::ckDispose(rsa)
        CkPrivateKey::ckDispose(key)
        ProcedureReturn
    EndIf

    ; Get the key as XML:
    keyXml.s
    keyXml = CkPrivateKey::ckGetXml(key)

    ; 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 = CkRsa::ckImportPublicKey(rsa,keyXml)
    If success <> 1
        Debug CkRsa::ckLastErrorText(rsa)
        CkRsa::ckDispose(rsa)
        CkPrivateKey::ckDispose(key)
        ProcedureReturn
    EndIf

    ; Encrypt a VISA credit card number:
    ; 1234-5678-0000-9999
    ccNumber.s = "1234567800009999"

    usePrivateKey.i = 0
    CkRsa::setCkEncodingMode(rsa, "base64")
    encryptedStr.s = CkRsa::ckEncryptStringENC(rsa,ccNumber,usePrivateKey)
    Debug "Encrypted:"
    Debug encryptedStr

    ; Now decrypt:
    rsaDecryptor.i = CkRsa::ckCreate()
    If rsaDecryptor.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkRsa::setCkEncodingMode(rsaDecryptor, "base64")
    success = CkRsa::ckImportPrivateKey(rsaDecryptor,keyXml)

    usePrivateKey = 1
    decryptedStr.s = CkRsa::ckDecryptStringENC(rsaDecryptor,encryptedStr,usePrivateKey)

    Debug "Decrypted:"
    Debug 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


    CkRsa::ckDispose(rsa)
    CkPrivateKey::ckDispose(key)
    CkRsa::ckDispose(rsaDecryptor)


    ProcedureReturn
EndProcedure