/// <summary>
/// Extract the next valid subkey set (Expired flag not set) as a KeyParam, and a CipherDescription structure.
/// <para>Used only when calling a Encryption function.</para>
/// </summary>
///
/// <param name="Description">out: The CipherDescription structure; the properties required to create a specific cipher instance</param>
/// <param name="KeyParam">out: The KeyParams class containing a unique key, initialization vector and HMAC key</param>
///
/// <returns>The KeyId array used to identify a subkey set; set as the KeyId in a MessageHeader structure</returns>
///
/// <exception cref="CryptoProcessingException">Thrown if the user has insufficient access rights to perform encryption with this key.</exception>
public byte[] NextKey(out CipherDescription Description, out KeyParams KeyParam)
{
if (!AccessScope.Equals(KeyScope.Creator))
{
throw new CryptoProcessingException("PackageFactory:NextKey", "You do not have permission to encrypt with this key!", new UnauthorizedAccessException());
}
try
{
// get the key data
MemoryStream keyStream = GetKeyStream();
// get the next unused key for encryption
int index = PackageKey.NextSubkey(keyStream);
if (index == -1)
{
throw new CryptoProcessingException("PackageFactory:NextKey", "The key file has expired! There are no keys left available for encryption.", new Exception());
}
// get the cipher description
Description = m_keyPackage.Description;
// store the subkey identity, this is written into the message header to identify the subkey
byte[] keyId = m_keyPackage.SubKeyID[index];
// get the starting position of the keying material within the package
long keyPos = PackageKey.SubKeyOffset(keyStream, keyId);
// no unused keys in the package file
if (keyPos == -1)
{
throw new CryptoProcessingException("PackageFactory:NextKey", "The key file has expired! There are no keys left available for encryption.", new Exception());
}
// get the keying material
KeyParam = GetKeySet(keyStream, m_keyPackage.Description, keyPos);
// mark the subkey as expired
PackageKey.SubKeySetPolicy(keyStream, index, (long)PackageKeyStates.Expired);
// write to file
WriteKeyStream(keyStream);
// return the subkey id
return(keyId);
}
catch
{
throw;
}
}