(Visual Basic 6.0) Streaming Encryption by Encrypting in Chunks

Encrypt data in chunks.

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

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

Dim crypt As New ChilkatCrypt2

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

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

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

Dim sbEncrypted As New ChilkatStringBuilder

' 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
Dim i As Long
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))

Debug.Print 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
Dim decryptedText As String
decryptedText = crypt.DecryptStringENC(sbEncrypted.GetAsString())

Debug.Print decryptedText

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