Method and apparatus for variable-overhead cached encryption

Abstract

A digital encryption structure allows the varying of the computational overhead by selectively reusing, according to the desired level of security, a pseudorandom encoding sequence at the transmitter end and by storing and reusing pseudorandom decoding sequences, associated with one or more transmitters at the receiver end. A public initialization vector is combined with a secret key to produce a deterministic sequence from a pseudorandom number generator. This pseudorandom sequence in turn, is used to convert plaintext to ciphertext. The sequence may be selectively reused by storing the sequence to a transmitter memory cache and iteratively reading the sequence from memory according to a counter which controls the level of security of the encryption system. The ciphertext is decrypted on the receiver end by invertibly combining the ciphertext with the same pseudorandom sequence used by the transmitter to originally encode the plaintext. The pseudorandom sequence is independently generated by the receiver end using the original key and initialization vector used in the transmitter end. Once generated in the receiver, the pseudorandom sequence is stored in a receiver cache for reuse with each iterative use of the stored transmitter pseudorandom sequence.