PureBasic

AES Encrypt and Decrypt a File

_LANGUAGE_ demonstrates how to AES encrypt a file of any size, and then decrypt. PureBasic

IncludeFile "CkCrypt2.pb"

Procedure ChilkatExample()

    success.i = 0

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

    crypt.i = CkCrypt2::ckCreate()
    If crypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkCrypt2::setCkCryptAlgorithm(crypt, "aes")

    ; CipherMode may be "ecb" or "cbc"
    CkCrypt2::setCkCipherMode(crypt, "cbc")

    ; KeyLength may be 128, 192, 256
    CkCrypt2::setCkKeyLength(crypt, 256)

    ; The padding scheme determines the contents of the bytes
    ; that are added to pad the result to a multiple of the
    ; encryption algorithm's block size.  AES has a block
    ; size of 16 bytes, so encrypted output is always
    ; a multiple of 16.
    CkCrypt2::setCkPaddingScheme(crypt, 0)

    ; An initialization vector is required if using CBC mode.
    ; ECB mode does not use an IV.
    ; The length of the IV is equal to the algorithm's block size.
    ; It is NOT equal to the length of the key.
    ivHex.s = "000102030405060708090A0B0C0D0E0F"
    CkCrypt2::ckSetEncodedIV(crypt,ivHex,"hex")

    ; The secret key must equal the size of the key.  For
    ; 256-bit encryption, the binary secret key is 32 bytes.
    ; For 128-bit encryption, the binary secret key is 16 bytes.
    keyHex.s = "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F"
    CkCrypt2::ckSetEncodedKey(crypt,keyHex,"hex")

    ; Encrypt a file, producing the .aes as output.
    ; The input file is unchanged, the output .aes contains the encrypted
    ; contents of the input file.

    ; Note: The .aes output file has no file format.  It is simply a stream
    ; of bytes that resembles random binary data.
    inFile.s = "/Users/chilkat/testData/pdf/sample.pdf"
    outFile.s = "/Users/chilkat/testData/p7m/sample.pdf.aes"
    success = CkCrypt2::ckCkEncryptFile(crypt,inFile,outFile)
    If success <> 1
        Debug CkCrypt2::ckLastErrorText(crypt)
        CkCrypt2::ckDispose(crypt)
        ProcedureReturn
    EndIf

    ; For demonstration purposes, a different instance of the object will be used
    ; for decryption.
    decrypt.i = CkCrypt2::ckCreate()
    If decrypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; All settings must match to be able to decrypt:
    CkCrypt2::setCkCryptAlgorithm(decrypt, "aes")
    CkCrypt2::setCkCipherMode(decrypt, "cbc")
    CkCrypt2::setCkKeyLength(decrypt, 256)
    CkCrypt2::setCkPaddingScheme(decrypt, 0)
    CkCrypt2::ckSetEncodedIV(decrypt,ivHex,"hex")
    CkCrypt2::ckSetEncodedKey(decrypt,keyHex,"hex")

    ; Decrypt the .aes
    inFile = "/Users/chilkat/testData/p7m/sample.pdf.aes"
    outFile = "/Users/chilkat/testData/pdf/recovered.pdf"
    success = CkCrypt2::ckCkDecryptFile(decrypt,inFile,outFile)
    If success = 0
        Debug CkCrypt2::ckLastErrorText(decrypt)
        CkCrypt2::ckDispose(crypt)
        CkCrypt2::ckDispose(decrypt)
        ProcedureReturn
    EndIf

    Debug "Success!"


    CkCrypt2::ckDispose(crypt)
    CkCrypt2::ckDispose(decrypt)


    ProcedureReturn
EndProcedure