It is hard to understand what reliability you mean.
To retrieve secure (encrypted) data and check it is original use authenticated encryption (i.e., an algorithm that gives security of data by encryption and a keyed authentication code like MAC). For reliability of work of cloud there are the notions like "proof of retrievability" where the cloud shows your data is still in storage.
For hiding the keys used in the cloud from being revealed one can use a random key for data encryption and encrypt that key with an RSA key of the cloud owner who does not store the secret key of the RSA (or any other public key can be used here instead of RSA) and only when retrieved the key will be sent to the user with the encrypted data. In summary: there are numerous reliability issues and your question is too unspecified.
Godd introduction to Mobile Cloud Computing (MCC) is presented in paper on: "Mobile Cloud Security Issues and Challenges: A Perspective" http://www.ijeit.com/Vol%203/Issue%201/IJEIT1412201307_73.pdf