public async Task StoreItem(string repo, string passphrase, string itemId, StoredItemMetadata meta, Stream dataStream)
{
var masterKey = await GetRepositoryMasterKey(repo, passphrase);
var iv = crypto.GenerateRandomIV();
meta = meta with {
Base64IV = Convert.ToBase64String(iv)
};
var encryptedStream = crypto.CreateEncryptionStream(dataStream, masterKey, iv);
await SetItemMetadata(repo, passphrase, itemId, meta);
await driver.WriteItem(repo, itemId, encryptedStream);
}