Cloud computing is an emerging paradigm in which resources of the computing infrastructure can be able to share over the internet. As this paradigm also have many challenges for data security and access control when users outsource their sensitive data in cloud servers. Secure and Efficient Data sharing in Cloud with single key size uses Key Aggregate cryptosystem (KAC) which is a public-key cryptosystem that produce constant-size ciphertexts for any set of secret key and make them compatible as single key as other data in cloud remains confidential. The limitation is that the number of ciphertext classes and the constant key size that makes the secret key predictable and data is unsecure. In this paper, the KAC-UC (KAC with Unbounded Ciphertext classes) scheme is proposed, in which the number of ciphertext classes in cloud storage is unbounded and the ciphertext classes can be extended by expanding the public and master key pair. The Variable size key is been used to securely share data that avoids the problem of being attacked and provides complexity for guessing the secret key. In addition, the ordered search is included to search the required data that is decrypted at the receiver side.