VBScript

Streaming Encryption by Encrypting in Chunks

See more Encryption Examples

Encrypt data in chunks. VBScript

Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

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

set crypt = CreateObject("Chilkat.Crypt2")

crypt.CryptAlgorithm = "aes"
crypt.CipherMode = "cbc"
crypt.KeyLength = 128

crypt.SetEncodedKey "000102030405060708090A0B0C0D0E0F","hex"
crypt.SetEncodedIV "000102030405060708090A0B0C0D0E0F","hex"

crypt.EncodingMode = "hex"
txt1 = "The quick brown fox jumped over the lazy dog." & vbCrLf
txt2 = "-" & vbCrLf
txt3 = "Done." & vbCrLf

set sbEncrypted = CreateObject("Chilkat.StringBuilder")

' 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.)
crypt.FirstChunk = 1
crypt.LastChunk = 0
success = sbEncrypted.Append(crypt.EncryptStringENC(txt1))

' Encrypt the 2nd chunk
crypt.FirstChunk = 0
crypt.LastChunk = 0
success = sbEncrypted.Append(crypt.EncryptStringENC(txt2))

' 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...
crypt.FirstChunk = 0
crypt.LastChunk = 0

For i = 0 To 4
    success = sbEncrypted.Append(crypt.EncryptStringENC(txt1))
    success = sbEncrypted.Append(crypt.EncryptStringENC(txt2))
Next

' Now encrypt the last chunk:
crypt.FirstChunk = 0
crypt.LastChunk = 1
success = sbEncrypted.Append(crypt.EncryptStringENC(txt3))

outFile.WriteLine(sbEncrypted.GetAsString())

' Now decrypt in one call.
' (The data we're decrypting is both the first AND last chunk.)  
crypt.FirstChunk = 1
crypt.LastChunk = 1
decryptedText = crypt.DecryptStringENC(sbEncrypted.GetAsString())

outFile.WriteLine(decryptedText)

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

outFile.Close