Remarks on using RSA with low exponent in a public network

Abstract

The authors give a counterexample to show that the RSA-based cryptosystem with low exponent proposed by Lee and Chang (Computer Communications 21 (1998)) is vulnerable to the low exponent attack with respect to their suggested lower boundary for the size of the public encryption key. That is, an eavesdropper can recover the plaintext from the ciphertext without knowing the secret decryption key, even though the size of the secret decryption key is large enough. The authors also suggest a new lower boundary for the size of the public encryption key for the Lee-Chang cryptosystem to enforce secrecy.