Security of the Cao-Li Public Key Cryptosystem

We show that the Cao-Li cryptosystem proposed in [1] is not secure. Its private key can be reconstructed from its public key using elementary means such as LU-decomposition and Euclidean algorithm. The Cao-Li public key cryptosystem was first proposed in [1]. It encrypts messages using a bilinear form that is chosen to permit easy decryption by the Chinese remainder theorem. Public key cryptosystems that are designed along this line are not uncommon in the Chinese cryptographic literature. However, as most of the original papers were published in Chinese, they remained relatively obscure until a few of them were described in [2] (in English) recently. Our description below is based on the latter reference.