(DataFlex) Tips on Matching Encryption with another System

This example provides tips on matching encryption results produced by another system.

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

Use ChilkatAx-9.5.0-win32.pkg

Procedure Test
    Handle hoCrypt
    String sIvHex1
    String sIvHex2
    String sKeyHex
    String sTemp1

    // This example assumes 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

    // Let's examine 256-bit AES encryption in CBC mode.
    // CBC mode is Cipher Block Chaining, and it uses an IV (initialization vector)
    Set ComCryptAlgorithm Of hoCrypt To "aes"
    Set ComCipherMode Of hoCrypt To "cbc"
    Set ComKeyLength Of hoCrypt To 256
    Set ComPaddingScheme Of hoCrypt To 0
    Move "000102030405060708090A0B0C0D0E0F" To sIvHex1
    Move "FF0102030405060708090A0B0C0D0E0F" To sIvHex2
    Send ComSetEncodedIV To hoCrypt sIvHex1 "hex"
    Move "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F" To sKeyHex
    Send ComSetEncodedKey To hoCrypt sKeyHex "hex"

    // Matching encryption requires all of the above settings to be matched exactly.
    // Let's get our output in hex format so we can easily see the values of the encrypted bytes.
    Set ComEncodingMode Of hoCrypt To "hex"

    // Encrypt something small:
    Get ComEncryptStringENC Of hoCrypt "Hello" To sTemp1
    Showln sTemp1
    // The result is 5B827AB3B4F9F2292C2B74C8A6C99A3D
    // This 16 bytes -- exactly one AES encryption block.

    // Let's change only the padding scheme.
    Set ComPaddingScheme Of hoCrypt To 3

    // Encrypt again:
    Get ComEncryptStringENC Of hoCrypt "Hello" To sTemp1
    Showln sTemp1
    // The result is entirely different: 469C28CC576069F807891FEE2DE76D68

    // The padding scheme only affects the very last block of output.  Therefore,
    // if all settings match except for the padding scheme, we're unable to
    // know if we encrypt a very small amount of data. However, if we encrypt
    // a larger amount of data, the single difference becomes apparent:
    Showln "-- Only the padding scheme differs --"
    Set ComPaddingScheme Of hoCrypt To 0
    Get ComEncryptStringENC Of hoCrypt "HelloHelloHelloHelloHelloHelloHello" To sTemp1
    Showln sTemp1
    Set ComPaddingScheme Of hoCrypt To 3
    Get ComEncryptStringENC Of hoCrypt "HelloHelloHelloHelloHelloHelloHello" To sTemp1
    Showln sTemp1

    // Now examine the outputs:
    // F6A201F8E0B6595FA20E4A212A2AD9A5046DAF29E8B35AD15CEE56A1A69F2A3A7B347A7C15E26E7A6760533C7A8E0D44
    // F6A201F8E0B6595FA20E4A212A2AD9A5046DAF29E8B35AD15CEE56A1A69F2A3A292CA61D03A85E1AC39B50D4DA71691E
    // We can see the output matches except for the last block, which is affected by the padding scheme.

    // If we are able to easily use ECB mode w/ the other system
    // we are trying to match, then eliminate the IV from the picture.
    // If the encryption matches in ECB mode, but not in CBC mode,
    // then we know all correct except for the IV.
    // For example, you can see how the IV changes everything with CBC mode,
    // but it's not used in ECB mode:
    Set ComPaddingScheme Of hoCrypt To 0
    Set ComCipherMode Of hoCrypt To "cbc"
    Showln "-- Only the IV differs, CBC mode produces different output. --"
    Send ComSetEncodedIV To hoCrypt sIvHex1 "hex"
    Get ComEncryptStringENC Of hoCrypt "HelloHelloHelloHelloHelloHelloHello" To sTemp1
    Showln sTemp1
    Send ComSetEncodedIV To hoCrypt sIvHex2 "hex"
    Get ComEncryptStringENC Of hoCrypt "HelloHelloHelloHelloHelloHelloHello" To sTemp1
    Showln sTemp1

    Set ComCipherMode Of hoCrypt To "ecb"
    Showln "-- Only the IV differs, ECB does not use the IV.  The outputs are the same. --"
    Send ComSetEncodedIV To hoCrypt sIvHex1 "hex"
    Get ComEncryptStringENC Of hoCrypt "HelloHelloHelloHelloHelloHelloHello" To sTemp1
    Showln sTemp1
    Send ComSetEncodedIV To hoCrypt sIvHex2 "hex"
    Get ComEncryptStringENC Of hoCrypt "HelloHelloHelloHelloHelloHelloHello" To sTemp1
    Showln sTemp1

    // If we can eliminate the padding scheme and IV from the degrees of freedom,
    // then the only remaining likely differences are (1) the secret key,
    // and (2) the input data itself.

    // The secret key is composed of binary bytes of exactly KeyLength bits.
    // For 256-bit AES encrytion, the key length is 256, and therefore the 
    // secret key is exactly 32 bytes.  (32 * 8 bits/byte = 256 bits)
    // If the secret key is derived from an arbitrary password string, then one must
    // exactly duplicate the derivation scheme (such as PBKDF2, for example)
    // The input bytes to the derivation scheme must also match.  For example,
    // is it the utf-8 byte representation of the password string that is used
    // as the starting point for the derivation, or perhaps utf-16, or ANSI (1 byte per char)?

    // Likewise, if the data being encrypted is a string, what byte representation of
    // the string is being encrypted?  If the bytes presented to the encryptor are different,
    // then the output is different.


End_Procedure