Pseudonymous Signature Schemes.

The chapter concerns cryptographic schemes enabling to sign digital data in a pseudonymized way. The schemes aim to provide a strong cryptographic evidence of integrity of the signed data and origin of the signature, but at the same time have to hide the identity of the signatory. There are two crucial properties that are specific for pseudonymous signatures: ability to recover the real identity of the signatory in certain circumstances and resilience to Sybil attacks. Despite using a single private key, the signatory can create a (single) unlinkable pseudonym for each domain or sector of activity and generate signatures corresponding to this pseudonym.