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(VBScript) Encrypt File in Chunks using AES CBCDemonstrates how to use the FirstChunk/LastChunk properties to encrypt a file chunk-by-chunk. Important This example requires Chilkat v9.5.0.68 or later.
Dim fso, outFile Set fso = CreateObject("Scripting.FileSystemObject") Set outFile = fso.CreateTextFile("output.txt", True) ' This example requires the Chilkat Crypt API to have been previously unlocked. ' See Unlock Chilkat Crypt for sample code. set crypt = CreateObject("Chilkat_9_5_0.Crypt2") crypt.CryptAlgorithm = "aes" crypt.CipherMode = "cbc" crypt.KeyLength = 128 crypt.SetEncodedKey "000102030405060708090A0B0C0D0E0F","hex" crypt.SetEncodedIV "000102030405060708090A0B0C0D0E0F","hex" fileToEncrypt = "qa_data/hamlet.xml" set facIn = CreateObject("Chilkat_9_5_0.FileAccess") success = facIn.OpenForRead(fileToEncrypt) If (success <> 1) Then outFile.WriteLine("Failed to open file that is to be encrytped.") WScript.Quit End If outputEncryptedFile = "qa_output/hamlet.enc" set facOutEnc = CreateObject("Chilkat_9_5_0.FileAccess") success = facOutEnc.OpenForWrite(outputEncryptedFile) If (success <> 1) Then outFile.WriteLine("Failed to encrypted output file.") WScript.Quit End If ' Let's encrypt in 10000 byte chunks. chunkSize = 10000 numChunks = facIn.GetNumBlocks(chunkSize) crypt.FirstChunk = 1 crypt.LastChunk = 0 set bd = CreateObject("Chilkat_9_5_0.BinData") i = 0 Do While i < numChunks i = i + 1 If (i = numChunks) Then crypt.LastChunk = 1 End If ' Read the next chunk from the file. ' The last chunk will be whatever amount remains in the file.. success = bd.Clear() success = facIn.FileReadBd(chunkSize,bd) ' Encrypt. success = crypt.EncryptBd(bd) ' Write the encrypted chunk to the output file. success = facOutEnc.FileWriteBd(bd,0,0) crypt.FirstChunk = 0 Loop ' Make sure both FirstChunk and LastChunk are restored to 1 after ' encrypting or decrypting in chunks. Otherwise subsequent encryptions/decryptions ' will produce unexpected results. crypt.FirstChunk = 1 crypt.LastChunk = 1 facIn.FileClose facOutEnc.FileClose ' Decrypt the encrypted output file in a single call using CBC mode: decryptedFile = "qa_output/hamlet_dec.xml" success = crypt.CkDecryptFile(outputEncryptedFile,decryptedFile) ' Assume success for the example.. ' Compare the contents of the decrypted file with the original file: bSame = facIn.FileContentsEqual(fileToEncrypt,decryptedFile) outFile.WriteLine("bSame = " & bSame) outFile.Close |
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