Implementing AES encryption in F# (according to MSDN C# example)

Question

Probably I have a stupid question, but I am not able to make it working. I am doing the AES encryption\decryption in F# according to the MSDN example which is in C#:

http://msdn.microsoft.com/en-us/library/system.security.cryptography.aes.aspx

My encryption method is as follows:

let EncryptStringToBytesAes (plainText : string) (key : byte[]) (iv : byte[]) =
    use aesAlg = Aes.Create()
    aesAlg.Key <- key
    aesAlg.IV <- iv
    // Create a decrytor to perform the stream transform.
    let encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV)
    // Create the streams used for encryption. 
    use msEncrypt = new MemoryStream()
    use csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)
    use swEncrypt = new StreamWriter(csEncrypt)
    swEncrypt.Write(plainText)
    msEncrypt.ToArray()

The problem is that this method always returns me an empty array of bytes. I do not have any exception. Key and IV are proper arrays of bytes. Seems like the StreamWriter is not working...

Thank you for help.

Answer 1

Building on @usr's answer...

The easiest way to make sure the stream is closed is to place the use statements within a block that goes out of scope before ToArray is called.

let EncryptStringToBytesAes (plainText : string) (key : byte[]) (iv : byte[]) =
    use aesAlg = Aes.Create()
    aesAlg.Key <- key
    aesAlg.IV <- iv
    // Create a decrytor to perform the stream transform.
    let encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV)
    // Create the streams used for encryption. 
    use msEncrypt = new MemoryStream()
    (
      use csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)
      use swEncrypt = new StreamWriter(csEncrypt)
      swEncrypt.Write(plainText)
    )
    msEncrypt.ToArray()