What is Signcryption?

To avoid forgery and ensure the confidentiality of a letter, it is a common practice for the originator of the letter to sign it and then seal the signed letter in an envelope. The same two-step approach can be adapted to the digital world where the originator of a digital message can ensure the unforgeability and confidentiality of the message by signing the message using a digital signature algorithm followed by encrypting the digitally signed message using a public key encryption algorithm.

Cryptographic operations for signature and encryption are relatively expensive as they typically involve computations on astronomically large numbers and generate additional communication overhead. With the "digital signature followed by public key encryption" method described above, the computational and communication overhead for achieving unforgeability and confidentiality is the sum of the overhead for digital signature and that for public key encryption.

Signcryption is a public key cryptographic method that achieves unforgeability and confidentiality simultaneously with significantly smaller overhead than that required by "digital signature followed by public key encryption". It does this by signing and encrypting a message in a single step, fulfilling a cryptographer's dream to " kill two birds with one stone ".