bbs

Documentation

Overview

Package bbs provides implementations of BBS+ key management and primitives.

The functionality of BBS+ signatures/proofs is represented as a pair of primitives (interfaces):

• Signer for signing a list of messages with a private key

• Verifier for verifying a signature against a list of messages, deriving a proof from a signature for a given set of sub messages and verifying such derived proof.

Example:

 package main

 import (
     "bytes"

     "github.com/google/tink/go/keyset"

     "github.com/dellekappa/kms-go/crypto/tinkcrypto/primitive/bbs"
 )

 func main() {
     // create signer keyset handle
     kh, err := keyset.NewHandle(bbs.BLS12381G2KeyTemplate())
     if err != nil {
         //handle error
     }

     // extract signer public keyset handle and key for signature verification and proof derivation/verification
     verKH, err := kh.Public()
     if err != nil {
         //handle error
     }

		// finally get the BBS+ signing primitive from the private key handle created above
		s:= bbs.NewSigner(kh)

		// create a message to be signed
		messages := [][]byte{[]byte("message 1"), []byte("message 2"), []byte("message 3"), []byte("message 4")}

		// and now sign using s
     sig, err = s.Sign(messages)
     if err != nil {
         // handle error
     }

		// to verify, get the BBS+ verification primitive from the public key handle created earlier above
     v := bbs.NewVerifier(verKH)

		// and verify signature
     err = v.Verify(messages, sig)
     if err != nil {
         // handle error
     }

		// to derive a proof from the bbs signature, create the indices of the messages to be revealed by the proof
		revealedIndexes := []int{0, 2}

		// and a nonce
		nonce := make([]byte, 10)

		_, err = rand.Read(nonce)
     if err != nil {
         // handle error
     }

		// then derive a proof for messages at index 0 and 2 as follows
		proof, err := verifier.DeriveProof(messages, sig, nonce, revealedIndexes)
     if err != nil {
         // handle error
     }

		// create a copy of the revealed messages to the party that should only access messages at index 0 and 2
		revealedMsgs := [][]byte{messages[0], messages[2]}

		// finally to verify the proof's authenticity for revealedMsgs, do the following
		err = verifier.VerifyProof(revealedMsgs, proof, nonce)
     if err != nil {
         // handle error
     }
 }

Index

• func BLS12381G2KeyTemplate() *tinkpb.KeyTemplate
• func NewSigner(h *keyset.Handle) (bbsapi.Signer, error)
• func NewSignerWithKeyManager(h *keyset.Handle, km registry.KeyManager) (bbsapi.Signer, error)
• func NewVerifier(h *keyset.Handle) (bbsapi.Verifier, error)
• func NewVerifierWithKeyManager(h *keyset.Handle, km registry.KeyManager) (bbsapi.Verifier, error)

Functions

func BLS12381G2KeyTemplate

func BLS12381G2KeyTemplate() *tinkpb.KeyTemplate

BLS12381G2KeyTemplate creates a Tink key template for BBS+ on BLS12-381 curve with G2 group.

func NewSigner

func NewSigner(h *keyset.Handle) (bbsapi.Signer, error)

NewSigner returns a BBS Signer primitive from the given keyset handle.

func NewSignerWithKeyManager

func NewSignerWithKeyManager(h *keyset.Handle, km registry.KeyManager) (bbsapi.Signer, error)

NewSignerWithKeyManager returns a BBS Signer primitive from the given keyset handle and custom key manager.

func NewVerifier

func NewVerifier(h *keyset.Handle) (bbsapi.Verifier, error)

NewVerifier returns a Verifier primitive from the given keyset handle.

func NewVerifierWithKeyManager

func NewVerifierWithKeyManager(h *keyset.Handle, km registry.KeyManager) (bbsapi.Verifier, error)

NewVerifierWithKeyManager returns a Verifier primitive from the given keyset handle and custom key manager.