Data deduplication is one of the most important data compression techniques, used for removing identical copies of repetitive data. For reduce duplication of data authorized duplication system is used. When a user uploads a file on the cloud, the file is split into a number of blocks, each block having a size of 4KB. Block is encrypted using a convergent key and subsequently a token is generated for it by using token generation algorithm. After encrypting the data using convergent key, users retain the key before sending the cipher-text to the cloud.