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Data security is of utmost importance in today's world. Especially when the data is travelling through an insecure communication network. There are symmetric key encryption techniques which use only one key for both encryption and decryption of the data. They are simple in design but can be easily cracked using brute force attacks. The entire security of such a cipher could be compromised if the attacker anyhow gets access to the keys. On the other hand, there are asymmetric key based algorithms which use a pair of keys, one for encryption, and the other for decryption, whose security is higher as compared to the symmetric ones but lack in time efficiency. It is also difficult to manage such a huge base of key-pairs efficiently and safely. This paper mainly focusses on the implementation of a system capable of encryption and decryption of multimedia data (Text, Images, Videos, Audio etc.) using a hybrid model based on the amalgamation of symmetric encryption techniques such as AES and asymmetric techniques such as ECC. ECC is based on the toughness of the discrete logarithm problem (DLP), whose public key is short, network bandwidth is little and ability to resist to attack is strong which makes it really difficult to guess the keys. Even if the attacker gets access to any of the keys, he or she won’t be in a position to decipher it in a relatively finite amount of man-years.

We extend the generic framework of reproducibility for reuse of randomness in multi-recipient encryption schemes as proposed by Bel- lare et al. (PKC 2003). A new notion of weak reproducibility captures not only encryption schemes which are (fully) reproducible under the criteria given in the previous work, but also a class of efficient schemes which can only be used in the single message setting. In particular, we are able to capture the single message schemes suggested by Kurosawa (PKC 2002), which are more efficient than the direct adaptation of the multiple mes- sage schemes studied by Bellare et al. Our study of randomness reuse in key encapsulation mechanisms provides an additional argument for the relevance of these results: by taking advantage of our weak reproducibil- ity notion, we are able to generalise and improve multi-recipient KEM constructions found in literature. We also propose an efficient multi- recipient KEM provably secure in the standard model and conclude the paper by proposing a notion of direct reproducibility which enables tighter security reductions.