Crate modified_bbs_for_PoC

Implements the BBS+ signature as defined in https://eprint.iacr.org/2016/663.pdf in Section 4.3. Also included is ability to do zero-knowledge proofs as described in Section 4.4 and 4.5.

The BBS+ signature is a pairing-based ECC signature that signs multiple messages instead of just one. The signature and messages can be used to create signature proofs of knowledge in zero-knowledge proofs in which the signature is not revealed and messages can be selectively disclosed––some are revealed and some remain hidden.

The signature also supports separating the signer and signature holder where the holder creates commitments to messages which are hidden from the signer and a signature blinding factor which is retained. The holder sends the commitment to the signer who completes the signing process and sends the blinded signature back. The holder can then un-blind the signature finishing a 2-PC computation

BBS+ signatures can be used for TPM DAA attestations or Verifiable Credentials.

Modules

• errors
  The errors that BBS+ throws
• issuer
  Represents steps taken by the issuer to create a BBS+ signature whether its 2PC or all in one
• keys
  BBS+ key classes
• messages
  Proof messages
• pok_sig
  Methods and structs for creating signature proofs of knowledge
• pok_vc
  Macros and classes used for creating proofs of knowledge Proof of knowledge of committed values in a vector Pedersen commitment––Commit and Prove scheme.
• prelude
  Convenience importer
• prover
  Represents steps taken by the prover to receive a BBS+ signature and generate ZKPs
• signature
  Methods and structs for creating signatures
• verifier
  Represents steps taken by the verifier to request signature proofs of knowledge and selective disclosure proofs

Macros

• pm_hidden
  Creates a proof message that is hidden based on the number of parameters One means hidden and only used in this proof Two means hidden but can be used in other proofs
• pm_hidden_raw
  Wrap a raw message in its respective hidden
• pm_revealed
  Creates a proof message to be revealed
• pm_revealed_raw
  Wrap a raw message in a revealed enum
• sm_map
  Creates the BTreeMap used for blind signing

Structs

• BlindSignatureContext
  Contains the data used for computing a blind signature and verifying proof of hidden messages from a prover
• Commitment
  The type for creating commitments to messages that are hidden during issuance.
• CommitmentBuilder
  Convenience wrapper for creating commitments
• GeneratorG1
  Wrapper for G1
• GeneratorG2
  Wrapper for G2
• ProofChallenge
  The Fiat-Shamir Challenge in proofs
• ProofNonce
  The type for nonces
• ProofRequest
  Contains the data from a verifier to a prover
• SignatureBlinding
  The type for blinding factors
• SignatureMessage
  The type for messages
• SignatureProof
  Contains the data from a prover to a verifier

Constants

• FR_COMPRESSED_SIZE
  Number of bytes in scalar compressed form
• FR_UNCOMPRESSED_SIZE
  Number of bytes in scalar uncompressed form
• G1_COMPRESSED_SIZE
  Number of bytes in G1 X coordinate
• G1_UNCOMPRESSED_SIZE
  Number of bytes in G1 X and Y coordinates
• G2_COMPRESSED_SIZE
  Number of bytes in G2 X (a, b) coordinate
• G2_UNCOMPRESSED_SIZE
  Number of bytes in G2 X(a, b) and Y(a, b) coordinates

Traits

• HashElem
  Struct can be generated from hashing
• RandomElem
  Struct can be generated randomly
• ToVariableLengthBytes
  Trait for structs that have variable length bytes but use compressed Bls12 elements

Functions

• hash_to_fr