Patent ID: 8108678

Claim:
An identity-based-encryption (IBE) signcryption method in which a sender signs and encrypts a message M for a recipient, comprising: at the sender, digitally signing and encrypting, with computing equipment, a message M in a signcryption operation using an IBE private key of the sender SK A and an IBE public key of the recipient ID B that is based on the recipient's identity to generate a ciphertext C that is a signed and encrypted version of the message M; sending, with computing equipment, the ciphertext C to the recipient anonymously, wherein an attacker cannot deduce the authorship of the message from the ciphertext C; at the recipient, decrypting, with computing equipment, the ciphertext C using an IBE private key SK B of the recipient that corresponds to the IBE public key ID B , wherein decrypting the ciphertext produces an unencrypted version of the message M and an IBE public key of the sender ID A that corresponds to the IBE private key SK A ; and at the recipient or at a third party, after the ciphertext has been decrypted by the recipient, performing, with computing equipment, signature verification in an operation that is separate from the decryption of the ciphertext, wherein performing the signature verification comprises using the decrypted message M and the IBE public key of the sender ID A to prove that the sender signed the message M.