(DataFlex) Encrypting/decrypting a data stream.

This example demonstrates how to encrypt (using a symmetric encryption algorithm such as AES, ChaCha20, Blowfish, RC2, 3DES, etc) a large amount of data. The data is passed in chunks to one of the encrypt methods: EncryptBytes, EncryptString, EncryptBytesENC, or EncryptStringENC, etc. The FirstChunk and LastChunk properties are used to indicate whether a chunk is the first, middle, or last in a stream to be encrypted. By default, both FirstChunk and LastChunk equal True -- meaning that the data passed is the entire amount.

Note: You may feed the data in chunks that are smaller than the block size of the encryption algorithm (AES and Twofish have a block size of 16 bytes. DES, 3DES, Blowfish, and RC2 have a block size of 8 bytes. ARC4 and ChaCha20 are streaming encryption algorithms and don't have a block size, but technically you can think of it as having a block size of 1 byte.)

Chilkat will buffer the data as required. If an amount of data smaller than the block size is passed such that the entire amount is buffered, then an empty string (or 0 bytes) is returned. The buffered data will be added to the data passed in subsequent calls. When the final data chunk is passed, it is padded to the encryption algorithm's block size (according to the PaddingScheme property) and the encryption is complete.

Decrypting in chunks is identical to encrypting in chunks.

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

Use ChilkatAx-win32.pkg

Procedure Test
    Handle hoCrypt
    String sTxt1
    String sTxt2
    String sTxt3
    Handle hoSbEncrypted
    Boolean iSuccess
    Integer i
    String sDecryptedText
    String sTemp1

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

    Get Create (RefClass(cComChilkatCrypt2)) To hoCrypt
    If (Not(IsComObjectCreated(hoCrypt))) Begin
        Send CreateComObject of hoCrypt
    End

    Set ComCryptAlgorithm Of hoCrypt To "aes"
    Set ComCipherMode Of hoCrypt To "cbc"
    Set ComKeyLength Of hoCrypt To 128

    Send ComSetEncodedKey To hoCrypt "000102030405060708090A0B0C0D0E0F" "hex"
    Send ComSetEncodedIV To hoCrypt "000102030405060708090A0B0C0D0E0F" "hex"

    Set ComEncodingMode Of hoCrypt To "hex"
    Move "The quick brown fox jumped over the lazy dog." + (character(13)) + (character(10)) To sTxt1
    Move "-" + (character(13)) + (character(10)) To sTxt2
    Move "Done." + (character(13)) + (character(10)) To sTxt3

    Get Create (RefClass(cComChilkatStringBuilder)) To hoSbEncrypted
    If (Not(IsComObjectCreated(hoSbEncrypted))) Begin
        Send CreateComObject of hoSbEncrypted
    End

    // Encrypt the 1st chunk:
    // (don't worry about feeding the data to the encryptor in 
    // exact multiples of the encryption algorithm's block size.
    // Chilkat will buffer the data.)
    Set ComFirstChunk Of hoCrypt To True
    Set ComLastChunk Of hoCrypt To False
    Get ComEncryptStringENC Of hoCrypt sTxt1 To sTemp1
    Get ComAppend Of hoSbEncrypted sTemp1 To iSuccess

    // Encrypt the 2nd chunk
    Set ComFirstChunk Of hoCrypt To False
    Set ComLastChunk Of hoCrypt To False
    Get ComEncryptStringENC Of hoCrypt sTxt2 To sTemp1
    Get ComAppend Of hoSbEncrypted sTemp1 To iSuccess

    // Now encrypt N more chunks...
    // Remember -- we're doing this in CBC mode, so each call
    // to the encrypt method depends on the state from previous
    // calls...
    Set ComFirstChunk Of hoCrypt To False
    Set ComLastChunk Of hoCrypt To False

    For i From 0 To 4
        Get ComEncryptStringENC Of hoCrypt sTxt1 To sTemp1
        Get ComAppend Of hoSbEncrypted sTemp1 To iSuccess
        Get ComEncryptStringENC Of hoCrypt sTxt2 To sTemp1
        Get ComAppend Of hoSbEncrypted sTemp1 To iSuccess
    Loop

    // Now encrypt the last chunk:
    Set ComFirstChunk Of hoCrypt To False
    Set ComLastChunk Of hoCrypt To True
    Get ComEncryptStringENC Of hoCrypt sTxt3 To sTemp1
    Get ComAppend Of hoSbEncrypted sTemp1 To iSuccess

    Get ComGetAsString Of hoSbEncrypted To sTemp1
    Showln sTemp1

    // Now decrypt in one call.
    // (The data we're decrypting is both the first AND last chunk.)  
    Set ComFirstChunk Of hoCrypt To True
    Set ComLastChunk Of hoCrypt To True
    Get ComGetAsString Of hoSbEncrypted To sTemp1
    Get ComDecryptStringENC Of hoCrypt sTemp1 To sDecryptedText

    Showln sDecryptedText

    // Note: You may decrypt in N chunks by setting the FirstChunk
    // and LastChunk properties prior to calling the Decrypt* methods


End_Procedure