Swift

Decrypt File in Chunks using 256-bit AES

See more Encryption Examples

Shows how to decrypt a file chunk-by-chunk using FirstChunk/LastChunk properties and accumulate the results in memory with a Chilkat BinData object. Swift

func chilkatTest() {
    var success: Bool = false

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

    // This example decrypts the file previously encrypted in this example:
    // Encrypt File in Chunks using AES CBC

    let crypt = CkoCrypt2()!

    crypt.cryptAlgorithm = "aes"
    crypt.cipherMode = "cbc"
    crypt.keyLength = 256

    crypt.setEncodedKey(keyStr: "000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F", encoding: "hex")
    crypt.setEncodedIV(ivStr: "000102030405060708090A0B0C0D0E0F", encoding: "hex")

    var fileToDecrypt: String? = "c:/temp/qa_output/hamlet.enc"
    let facIn = CkoFileAccess()!
    success = facIn.open(forRead: fileToDecrypt)
    if success != true {
        print("Failed to open file to be decrytped.")
        return
    }

    // Let's decrypt in 32000 byte chunks.
    var chunkSize: Int = 32000
    var numChunks: Int = facIn.getNumBlocks(blockSize: chunkSize).intValue

    crypt.firstChunk = true
    crypt.lastChunk = false

    let bd = CkoBinData()!
    let bdDecrypted = CkoBinData()!

    var i: Int = 0
    while i < numChunks {
        i = i + 1
        if i == numChunks {
            crypt.lastChunk = true
        }

        // Read the next chunk from the file.
        // The last chunk will be whatever amount remains in the file..
        bd.clear()
        facIn.fileReadBd(maxNumBytes: chunkSize, binData: bd)

        // Decrypt this chunk.
        crypt.decryptBd(bd: bd)
        // Accumulate the decrypted chunks.
        bdDecrypted.appendBd(binData: bd)

        crypt.firstChunk = false
    }

    // Make sure both FirstChunk and LastChunk are restored to true after
    // encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
    // will produce unexpected results.
    crypt.firstChunk = true
    crypt.lastChunk = true

    facIn.fileClose()

    // The fully decrypted file is contained in bdDecrypted.
    // You can save to a file if desired, or use the decrypted data in your application directly from bdDecrypted.
    bdDecrypted.writeFile(path: "c:/temp/qa_output/hamlet_decrypted.xml")

}