(Visual FoxPro) Streaming Encryption

Encrypt and decrypt using a stream.

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

LOCAL loCrypt
LOCAL lcIvHex
LOCAL lcKeyHex
LOCAL lcPlainText
LOCAL loStream
LOCAL loEStrings
LOCAL loTask
LOCAL lnSuccess
LOCAL lcCipherText
LOCAL i
LOCAL n

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt = CreateObject('Chilkat.Crypt2')

* Setup encryption using the chacha20 algorithm...
loCrypt.CryptAlgorithm = "chacha20"
loCrypt.KeyLength = 256
loCrypt.EncodingMode = "hex"
lcIvHex = "000000000000000000000002"
loCrypt.SetEncodedIV(lcIvHex,"hex")
loCrypt.InitialCount = 42
lcKeyHex = "1c9240a5eb55d38af333888604f6b5f0473917c1402b80099dca5cbc207075c0"
loCrypt.SetEncodedKey(lcKeyHex,"hex")

lcPlainText = "The quick brown fox jumped over the lazy dog." + CHR(13) + CHR(10)

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Stream')
loStream = CreateObject('Chilkat.Stream')

* We'll save the encrypted output in eStrings to demonstrate streaming decryption next.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringArray')
loEStrings = CreateObject('Chilkat.StringArray')

* Start a background task that will encrypt a stream.
loTask = loCrypt.EncryptStreamAsync(loStream)
lnSuccess = loTask.Run()

* Write plainText to the stream, and read chacha20 encrypted text..

FOR i = 1 TO 10
    * Note: An encryption algorithm's block size will cause buffering,
    * and therefore not every loop iteration will produce output.
    lnSuccess = loStream.WriteString(lcPlainText)
    IF (loStream.DataAvailable = 1) THEN
        lcCipherText = loStream.ReadBytesENC("hex")
        ? lcCipherText
        lnSuccess = loEStrings.Append(lcCipherText)
    ENDIF

NEXT

* Tell the background task that the stream has ended.
lnSuccess = loStream.WriteClose()

* Let's make sure the background task finished.
* It should already be the case that the task is finished.
DO WHILE (loTask.Finished <> 1)
    loTask.SleepMs(20)
ENDDO

* Get any remaining data available from the stream.
IF (loStream.DataAvailable = 1) THEN
    lcCipherText = loStream.ReadBytesENC("hex")
    ? lcCipherText
    lnSuccess = loEStrings.Append(lcCipherText)
ENDIF

IF (loTask.TaskSuccess <> 1) THEN
    ? "async encryption failed:"
    ? loTask.ResultErrorText
    lnSuccess = 0
ENDIF

RELEASE loTask

? "-- encrypt finished --"

* Now decrypt to return the original.

* Reset the stream object so it can be used again.
loStream.Reset()

* Start a background task that will decrypt a stream.
loTask = loCrypt.DecryptStreamAsync(loStream)
lnSuccess = loTask.Run()

n = loEStrings.Count
FOR i = 0 TO n - 1
    lnSuccess = loStream.WriteBytesENC(loEStrings.GetString(i),"hex")
    IF (loStream.DataAvailable = 1) THEN
        lcPlainText = loStream.ReadString()
        ? lcPlainText
    ENDIF

NEXT

* Tell the background task that the stream has ended.
lnSuccess = loStream.WriteClose()

* Let's make sure the background task finished.
* It should already be the case that the task is finished.
DO WHILE (loTask.Finished <> 1)
    loTask.SleepMs(20)
ENDDO

* Get any remaining data available from the stream.
IF (loStream.DataAvailable = 1) THEN
    lcPlainText = loStream.ReadString()
    ? lcPlainText
ENDIF

IF (loTask.TaskSuccess <> 1) THEN
    ? "async decryption failed:"
    ? loTask.ResultErrorText
    lnSuccess = 0
ENDIF

RELEASE loTask

? "-- decrypt finished --"

RELEASE loCrypt
RELEASE loStream
RELEASE loEStrings