public async Task <(Stream, StoredItemMetadata)> RetrieveItem(string repo, string passphrase, string itemId)
{
var masterKey = await GetRepositoryMasterKey(repo, passphrase);
var meta = await GetItemMetadata(repo, passphrase, itemId);
var encryptedStream = await driver.ReadItem(repo, itemId);
var dataStream = crypto.CreateDecryptionStream(encryptedStream, masterKey, Convert.FromBase64String(meta.Base64IV));
return(dataStream, meta);
}