An Enhanced Threshold Authenticated Encryption Scheme with Convertibility

Recently, Chung et al. (2009) proposed a novel and valuable threshold authenticated encryption scheme. Unfortunately, it has a potential weakness: if the secret message involves criminal evidence or illegal content, the designated receiver cannot authenticate the secret message in the later dispute. The authors of this paper aim at enhancing Chung et al.’s scheme by adding the convertibility capability so that the designated receiver can demonstrate that the signature with respect to the message has been signed. And then, the enforcement agency can trace the source of secret messages. In addition to inheriting the advantages of Chung et al.’s scheme, the improved scheme achieves the goal that the designated recipient can convert an authenticated signature into an ordinary signature. It is worthwhile to note that the main advantages are that, with the ordinary signature along with the signed message, the third party can verify if the authenticated signature was generated by a specific signer group. In this way, public verifiability to the authenticated encryption scheme is satisfied.