(DataFlex) Encrypting a Data Stream

This example illustrates encrypting a large dataset using symmetric encryption algorithms like AES, ChaCha20, Blowfish, etc. The data is processed in chunks using the EncryptStringENC method. The FirstChunk and LastChunk properties identify whether a chunk is the first, intermediate, or last in the encrypted stream. By default, both properties are set to True, indicating that the data provided represents the entire dataset.

You can provide data chunks smaller than the encryption algorithm's block size. For example, AES uses 16-byte blocks; 3DES, and Blowfish use 8-byte blocks; and ChaCha20, as a streaming algorithm, effectively has a block size of 1 byte.

Chilkat handles the buffering of data as needed. If a data chunk smaller than the block size is provided, an empty string (or 0 bytes) is returned, and the data is buffered to be combined with subsequent chunks. The final chunk is padded to the algorithm's block size (as determined by the PaddingScheme property) to complete the encryption process.

Chunk-wise decryption follows the same procedure as chunk-wise encryption.

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