In cryptography, signcryption is a public-key primitive that simultaneously performs the functions of both digital signature and encryption.
Signcryption is a relatively new cryptographic technique that is supposed to perform the functions of digital signature and encryption in a single logical step and can effectively decrease the computational costs and communication overheads in comparison with the traditional signature-then-encryption schemes.
This means that at least some aspect of its efficiency (for example the computation time) is better than any hybrid of digital signature and encryption schemes, under a particular model of security.
[2] There are also many other signcryption schemes that have been proposed throughout the years, each of them having its own problems and limitations, while offering different levels of security and computational costs.
Gen generates a pair of keys for any user, SC is generally a probabilistic algorithm, and USC is most likely deterministic.