signcrypted

Signcryption, sometimes referred to as signcrypted, is a cryptographic primitive that simultaneously provides confidentiality, authenticity, and integrity by combining digital signing and encryption into a single operation. The technique reduces computational and communication overhead compared with performing signing and encryption separately, and it simplifies protocol design for secure communications.

In a typical signcryption scheme, the sender uses their private key and the recipient’s public key to generate a signcrypted message. The signcrypted payload is transmitted and, upon receipt, the recipient uses their private key (and, in some constructions, the sender’s public key) to recover the plaintext and verify the sender’s identity in one step. Some variants allow public verification without access to private keys or support additional features such as forward secrecy.

Key advantages include providing confidentiality and authentication in one operation, lower public-key operation counts, and potentially smaller message sizes. A caveat is that non-repudiation depends on the exact design and can be less straightforward than with separate signatures; certain signcryption schemes prioritize efficiency and confidentiality, while others aim to preserve non-repudiation.

Variants of signcryption include public-key signcryption, identity-based signcryption, and multi-party or proxy signcryption. Security analyses typically prove properties such as confidentiality against chosen-plaintext or chosen-ciphertext attacks and unforgeability under standard cryptographic assumptions.

Applications include secure email, messaging, and document exchange where both privacy and origin verification are required, especially in environments with limited bandwidth or computational resources. Related concepts include traditional sign-then-encrypt, digital signatures, and public-key encryption, as well as ongoing research on standardization and interoperability.