(Swift 2) Decrypt 256-bit AES GCM Produced by Something Unknown

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM.

Chilkat Downloads for the Swift Programming Language MAC OS X (Cocoa) Objective-C/Swift Libs iOS Objective-C/Swift Libs

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

    // We have the following to decrypt:

    // Key (Base64): 
    var keyBase64: String? = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

    // IV (Base64Url):
    var ivBase64Url: String? = "xrvaINMLqotAbWRK"

    // ciphertext (base64url):
    var cipherBase64Url: String? = "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY="

    let crypt = CkoCrypt2()

    crypt.CryptAlgorithm = "aes"
    crypt.CipherMode = "gcm"
    crypt.KeyLength = 256

    var success: Bool = crypt.SetEncodedAad("random", encoding: "ascii")
    crypt.SetEncodedKey(keyBase64, encoding: "base64")
    crypt.SetEncodedIV(ivBase64Url, encoding: "base64url")

    // The cipher text contains the 16-byte auth tag at the end.
    // get it separately..
    let bdEncrypted = CkoBinData()
    let bdAuthTag = CkoBinData()
    success = bdEncrypted.AppendEncoded(cipherBase64Url, encoding: "base64url")

    var numBytes: Int = bdEncrypted.NumBytes.intValue
    var authTagHex: String? = bdEncrypted.GetEncodedChunk(numBytes - 16, numBytes: 16, encoding: "hex")

    print("Auth tag in hex: \(authTagHex!)")

    success = bdAuthTag.AppendEncoded(authTagHex, encoding: "hex")
    bdEncrypted.RemoveChunk(numBytes - 16, numBytes: 16)

    // Use this special value to tell Chilkat to ignore the auth tag.
    success = crypt.SetEncodedAuthTag("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", encoding: "hex")

    // Decrypt
    crypt.EncodingMode = "base64"
    var originalText: String? = crypt.DecryptStringENC(bdEncrypted.GetEncoded("base64"))
    if crypt.LastMethodSuccess == false {
        print("\(crypt.LastErrorText)")
    }
    else {
        print("\(originalText!)")
        print("Success.")
    }

    // Decrypted text

}