A General Encryption Scheme Based on MDS Code ( Extended Summary )

Many applications, such as wireless communications, high speed multimedia data streaming systems and sensor networks, call for strong ciphers with low computation complexity and high speed in encryption and decryption. Additive stream ciphers usually have lower computation complexity and thus provide higher encryption/decryption speed than block ciphers. An additive stream cipher usually encrypts a plaintext stream simply by adding it to a key stream, where the addition (⊕) is simple bitwise XOR (exclusive OR). Additive stream ciphers though have a main disadvantage that a known plaintext-ciphertext stream pair reveals the corresponding key stream used in encryption. The encryption key used to generate the key stream can then be deduced from a long enough key stream. Even two ciphertext streams encrypted using a same key stream can be exploited to obtain the key stream itself[3]. In fact, such a disadvantage of stream ciphers has been exploited to show the insecurity of the WEP (Wired Equivalent Privacy) protocol used in IEEE 802.11 standard for wireless networks [2]. Block ciphers, on the other hand, can conceal statistical properties of a plaintext more easily in the corresponding ciphertext. To keep the merits of both stream cipher and block cipher but lessen their disadvantages, it has been proposed to combining stream ciphers and block ciphers together to achieve stronger security [4]. Such combining, however, does not lessen computation complexity of encryption and decryption. In fact, computation complexity is even higher than that of the component block ciphers and stream ciphers. In this paper, we propose to combine cryptographically strong random key stream generators (including those used in stream ciphers) with simple block encoders to achieve both high cryptographic strength and low computation complexity of encryption and decryption. In particular, we show proper error correcting codes can be used as block encoders. In general, encoding and decoding of a proper block error (or more accurately erasure) correcting code is much faster than encryption and decryption of block ciphers.