Abstract: Cryptographic methods and systems are described. An example cryptographic system may include a signature engine to digitally sign a message using fuzzy data associated with a signee. The signature engine is configured to generate a digital signature using a lattice instantiation and a linear sketch. The linear sketch is configured based on the lattice instantiation. The digital signature is a function of the fuzzy data and the message and uses a signature-time signing key residing within a signing key space. The signing key space is a space defined by the lattice instantiation. An example of a verification engine is also described. The verification engine is configured to receive the message and the digital signature and to verify the message as signed by the signee.

Abstract: The disclosure relates to implementing an anonymous reputation system for managing user reviews. In one arrangement, an anonymous reputation system is constructed from a group of group signature schemes run in parallel. Each item of a plurality of items is associated uniquely with one of the group signature schemes. A user is allowed to join the group signature scheme associated with the item when information indicating that the user has performed a predetermined operation associated with the item is received. The user can submit a review of the item when the user has joined the group signature scheme associated with the item (6). The anonymous reputation system is publicly linkable and non-frameable (8a, 8b).