Encrypt.swift

extension Data {
    func encrypt(key: Data) {
        let ivData = Data.randomBytes(count: kCCKeySizeAES128)
        var tag = Data(count: kCCKeySizeAES128)
        var cipherText = Data(count: count)

        _ = cipherText.withUnsafeMutableBytes { (cipherPtr) in
            _ = tag.withUnsafeMutableBytes { (tagPtr) in
                _ = ivData.withUnsafeBytes { (ivPtr)  in
                    _ = key.withUnsafeBytes { (keyPtr) in
                        _ = keyPtr
                        _ = ivPtr
                        _ = tagPtr
                        _ = cipherPtr
                        // Do crypto stuff here
                    }
                }
            }
        }
    }
}

I get a compile error on line 12: 'inout Data' is not convertible to 'Data'