We introduce a new cryptographic problem called time capsule signature. Time capsule signature is a ‘future signature’ that becomes valid from a specific future time t, when a trusted third party (called Time Server) publishes some trapdoor information associated with the time t. In addition, time capsule signature should satisfy the following properties: (1) If the signer wants, she can make h...

As an extension of digital signature, designated confirmer signature (DCS) efficiently realizes the privacy protection of the signer. In a DCS scheme, the validity of the signature must be confirmed by the signer or a semi-trusted third party, called confirmer. Since the DCS signature is generated by encrypting a standard signature with the designated confirmer’s public key, only the confirmer ...