protected CryptoTransform GetTransform(string peerId)
{
CryptoTransform transform;
lock (_transforms)
{
if (!_transforms.TryGetValue(peerId, out transform))
{
// we prepend RijndaelV1 to peerId to make possible future changes to RijndaelEncryptionProvider logic (for example increasing key or IV size).
// if we use unchanged peerId (user id) then it will be impossilbe to store ecnryption keys of different sizes and encryption provider versioning will be broken.
var key =_encryptionEncryptionKeyProvider.GetEncryptionKey("RijndaelV1." + peerId, CryptoProvider.KeySize / 8, CryptoProvider.BlockSize / 8);
transform = new CryptoTransform(CryptoProvider.CreateEncryptor(key.Key, key.IV),
CryptoProvider.CreateDecryptor(key.Key, key.IV));
_transforms.Add(peerId, transform);
}
}
return transform;
}