signcryption

Signcryption is a cryptographic primitive that combines digital signing and encryption into a single operation. It is designed to provide both confidentiality and authenticity of a message more efficiently than the conventional approach of signing a plaintext and then encrypting the result.

In a typical signcryption scheme, the sender uses their private signing key and the recipient’s public encryption key to produce one signcrypted ciphertext. The recipient uses their private decryption key and the sender’s public verification key to recover the plaintext and verify the origin in a single step. Some designs also allow public verification of origin by third parties.

Benefits include reduced computational cost and bandwidth, since only one cryptographic operation is performed instead of separate sign-then-encrypt steps. This can translate into faster secure messaging and lower resource use in constrained environments. Signcryption also provides the same basic security properties as signing and encryption: confidentiality, integrity, and authenticity; some schemes offer additional features such as forward secrecy or public verifiability.

Security relies on the underlying algorithms and constructions; misuse or poor parameter choices can undermine protections. Not all signcryption schemes guarantee non-repudiation in the same way as standalone signatures, and some designs require careful key management and trusted setups. Compatibility with existing standards and interoperability can be an issue.

Variants include identity-based signcryption, designated-verifier signcryption, and public-verifiability signcryption. Signcryption is used in secure email, messaging, software updates, and other communications where both confidentiality and sender authentication are important.