Abstract: A method for managing a group signature scheme includes in a setup procedure for group initialization, generating, by a group manager, a group public key. In a join procedure for the group manager to add a new member to the group, the method includes generating by the new member, user information, and providing the generated user information to the group manager, and computing, by the group manager, membership information for the new member based on the user information received by the new member and on the group public key, and providing to the new member the computed membership information. In particular, the membership information is computed, by the group manager, as a function of the inverse of a given hash function of the user information. In a signing procedure for a group member to sign a message on behalf of the group, the method includes: using, by the group member, the membership information and the user information.

Abstract: A method for protecting sensitive data in an entry of a log file for later audit, which includes encrypting the sensitive data in the log entry by using a random cryptographic key for each auditor authorized to access the log entry, encrypting the random cryptographic key by using an auditor's personal cryptographic key, and for each auditor not authorized to access the log entry, encrypting a fake cryptographic key having the same properties as the random cryptographic key by using an auditor's personal cryptographic key.

Abstract: Communication between an administrator device and an administered device in a network is arranged in the form of a chain of digitally signed communication items including messages sent from an originator device to a recipient device. Each message has an associated respective digitally signed receipt, and the originator device is configured not to send a new item toward the recipient device in the absence of a respective digitally signed receipt for a previously sent item. With at least one, and preferably by both of the administrator device and the administered device, there is stored a history record of communication items exchanged therebetween. The history record is agreed upon and signed by both the administrator device and the administered device.

Abstract: A method for managing a group signature scheme includes in a setup procedure for group initialization, generating, by a group manager, a group public key. In a join procedure for the group manager to add a new member to the group, the method includes generating by the new member, user information, and providing the generated user information to the group manager, and computing, by the group manager, membership information for the new member based on the user information received by the new member and on the group public key, and providing to the new member the computed membership information. In particular, the membership information is computed, by the group manager, as a function of the inverse of a given hash function of the user information. In a signing procedure for a group member to sign a message on behalf of the group, the method includes: using, by the group member, the membership information and the user information.