Abstract: A signcryption is generated by a sender by using a first encryption algorithm to encrypt plaintext m with public key Epk to get ciphertext e, e=E.Encrypt(m); generating a key k and its encapsulation c using an encapsulation algorithm and public key Kpk, k,c=KD.Encapsulate( ); sign (e,c) using Ssk, s=S.sign(e,c); encrypt the signature s using a second encryption algorithm and the key k, e_d=D.Encrypt(s). The signcryption of m is formed by (e,c,e_d). The sender may also prove knowledge of the decryption of e, and that e_d encrypts a valid signature on the concatenation of c and e using the key of the encapsulation. Also provided are the corresponding signcryption verification device and method, and computer program products.

Abstract: The present invention improves on prior art group encryption schemes by encrypting an alias of a recipient's public key instead of the public key itself. A Group Manager publishes the encryption of the alias,the corresponding public key and a corresponding certificate on a public database DB. The alias is a resulting value of a suitably chosen function ƒ on the public key, and can be viewed as a hash of the public key. This can allow a significant decrease in the size and cost of the resulting construction as the alias can be made smaller than the public key. In particular, there is no need to apply the second encryption scheme as many times as there are group dements in the recipient's public key.

Abstract: A signcryption is generated by a sender by using a first encryption algoritm to encrypt plaintext m with public key Epk to get ciphertext e, e=E.Encrypt(m); generating a key k and its encapsulation c using an encapsulation algoritm and public key Kpk, k,c=KD.Encapsulate() sign (e,c) using Ssk, s=S.sign(e,c); encrypt the signature s using a second encryption algoritm and the key k, e_d=D.Encrypt(s). The signcryption of m is formed by (e,c,e_d). The sender may also prove knowledge of the decryption of e, and that e_d encrypts a valid signature on the concatenation of c and e using the key of the encapsulation. Also provided are the corresponding signcryption verification device and method, and computer program products.