/// <summary>
/// Write a copy of the current encrypted stream. Used to change meta-data
/// and encryption key(s) etc.
/// </summary>
/// <param name="outputStream"></param>
public void CopyEncryptedTo(DocumentHeaders outputDocumentHeaders, Stream cipherStream, ProgressContext progress)
{
if (outputDocumentHeaders == null)
{
throw new ArgumentNullException("outputDocumentHeaders");
}
if (cipherStream == null)
{
throw new ArgumentNullException("cipherStream");
}
if (!cipherStream.CanSeek)
{
throw new ArgumentException("The output stream must support seek in order to back-track and write the HMAC.");
}
if (DocumentHeaders == null)
{
throw new InternalErrorException("Document headers are not loaded");
}
using (HmacStream hmacStreamOutput = new HmacStream(outputDocumentHeaders.HmacSubkey.Key, cipherStream))
{
outputDocumentHeaders.WriteWithHmac(hmacStreamOutput);
using (AxCryptDataStream encryptedDataStream = _reader.CreateEncryptedDataStream(DocumentHeaders.HmacSubkey.Key, DocumentHeaders.CipherTextLength, progress))
{
CopyToWithCount(encryptedDataStream, hmacStreamOutput, progress);
if (_reader.Hmac != DocumentHeaders.Hmac)
{
throw new Axantum.AxCrypt.Core.Runtime.InvalidDataException("HMAC validation error in the input stream.", ErrorStatus.HmacValidationError);
}
}
outputDocumentHeaders.Hmac = hmacStreamOutput.HmacResult;
// Rewind and rewrite the headers, now with the updated HMAC
outputDocumentHeaders.WriteWithoutHmac(cipherStream);
cipherStream.Position = cipherStream.Length;
}
}