ABSTRACT
The fundamental feature which distinguishes public-key from symmetric-key schemes is the separation of encryption and decryption capabilities. To be slightly more precise, the key k in a public-key scheme is written as a key-pair k = (e, d), where e is used for encryption and d is used for decryption. In this context, e is the public key and need not be secret; d is the private key, and is held only by those needing to decrypt messages. To be useful as an encryption scheme, it must be computationally infeasible for an adversary in possession of e and ciphertext c to find m so that Ee (m) = c.
