In 1997 Yuliang Zheng presented a positive answer to the following question: “is it possible to transfer a message of arbitrary length in a secure and authenticated way with an expense less than that required by signature then encryption?”. This was for the first time, since public-key cryptography has been invented, that the question is addressed in literature. He discovered a new cryptographic primitive, called signcryption, which simultaneously fulfills both the functions of digital signature and public key encryption in a logically single step, and with a cost significantly smaller than that required by signature then encryption. The proposed cryptographic primitive is more efficient for both types of costs involved: computational cost and communication overhead. The computational cost represents how much computational effort has to be invested by the sender and by the receiver of the message. It is determined by counting the number of dominant operations involved. The communication overhead represents the extra bits which are appended to a message in case of a digital signature or encryption based on public key cryptography.

Encryption and digital signature are two fundamental cryptographic tools that can guarantee the confidentiality, integrity, and non-repudiation. Until signcryption, they have been viewed as important but distinct building blocks of various cryptographic systems. In public key schemes, a traditional method is to digitally sign a message then followed by an encryption, named signature-then-encryption. In many applications, both confidentiality and authenticity are needed together. Such applications include secure Email (S/MIME), secure shell (SSH), and secure web browsing (HTTPS). In order to accomplish these two goals; many cryptographic schemes have been created: Schnorr signature then ElGamal encryption, DSS then ElGamal encryption, RSA