fix: change the way of converting blank node ids

This fix improves the way of converting blank node ids before signing and verification, just using regexp-based string replacement. It enables us to make `credentialSubject.id` to be blank node identifier, which would be useful in privacy-preserving applications of BBS+.

fixes mattrglobal#128

__tests__/AnonymousVC.spec.ts

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2020 - MATTR Limited
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {
+  exampleBls12381KeyPair,
+  customLoader,
+  testAnonymousVcDocument,
+  testRevealAnonymousVcDocument,
+  testNestedRevealDocument,
+  testNestedRevealFullDocument,
+  testNestedAnonymousVcDocument
+} from "./__fixtures__";
+
+import jsigs from "jsonld-signatures";
+import {
+  Bls12381G2KeyPair,
+  BbsBlsSignatureProof2020,
+  BbsBlsSignature2020,
+  deriveProof
+} from "../src/index";
+import { getProofs } from "../src/utilities";
+
+const key = new Bls12381G2KeyPair(exampleBls12381KeyPair);
+
+const signDeriveVerify = async (vc: any, reveal: any, subject: any) => {
+  // Issuer issues VC
+  const signedVc = await jsigs.sign(vc, {
+    suite: new BbsBlsSignature2020({ key }),
+    purpose: new jsigs.purposes.AssertionProofPurpose(),
+    documentLoader: customLoader
+  });
+  expect(signedVc).toBeDefined();
+
+  // Holder verifies VC
+  const verifiedVc = await jsigs.verify(signedVc, {
+    suite: new BbsBlsSignature2020(),
+    purpose: new jsigs.purposes.AssertionProofPurpose(),
+    documentLoader: customLoader
+  });
+  expect(verifiedVc.verified).toBeTruthy();
+
+  // Holder derives Proof
+  const derivedProof = await deriveProof(signedVc, reveal, {
+    suite: new BbsBlsSignatureProof2020(),
+    documentLoader: customLoader
+  });
+  expect(derivedProof.credentialSubject).toEqual(subject);
+
+  // Verifier verifies proof
+  const { document, proofs } = await getProofs({
+    document: derivedProof,
+    proofType: BbsBlsSignatureProof2020.proofType,
+    documentLoader: customLoader
+  });
+  const suite = new BbsBlsSignatureProof2020();
+  const result = await suite.verifyProof({
+    document,
+    proof: proofs[0],
+    documentLoader: customLoader,
+    purpose: new jsigs.purposes.AssertionProofPurpose()
+  });
+  expect(result.verified).toBeTruthy();
+};
+
+describe("anonymous verifiable credentials with blank node identifiers", () => {
+  it("should sign, derive proof, and verify proof on anonymous verifiable credential", async () => {
+    await signDeriveVerify(
+      testAnonymousVcDocument,
+      testRevealAnonymousVcDocument,
+      {
+        id: "urn:bnid:_:c14n1",
+        type: ["Person", "PermanentResident"],
+        commuterClassification: "C1"
+      }
+    );
+  });
+
+  it("should sign, derive proof, and verify proof on anonymous nested and partially revealed verifiable credential", async () => {
+    await signDeriveVerify(
+      testNestedAnonymousVcDocument,
+      testNestedRevealDocument,
+      {
+        id: "urn:bnid:_:c14n2",
+        degree: {
+          id: "urn:bnid:_:c14n1",
+          type: "BachelorDegree",
+          name: "Bachelor of Science and Arts"
+        }
+      }
+    );
+  });
+
+  it("should sign, derive proof, and verify proof on anonymous nested and fully revealed verifiable credential", async () => {
+    await signDeriveVerify(
+      testNestedAnonymousVcDocument,
+      testNestedRevealFullDocument,
+      {
+        id: "urn:bnid:_:c14n2",
+        degree: {
+          id: "urn:bnid:_:c14n1",
+          type: "BachelorDegree",
+          name: "Bachelor of Science and Arts",
+          degreeType: "Underwater Basket Weaving"
+        },
+        college: "Contoso University"
+      }
+    );
+  });
+});

__tests__/__fixtures__/data/test_anonymous_vc.json

@@ -0,0 +1,27 @@
+{
+  "@context": [
+    "https://www.w3.org/2018/credentials/v1",
+    "https://w3id.org/citizenship/v1",
+    "https://w3id.org/security/v3-unstable"
+  ],
+  "type": ["VerifiableCredential", "PermanentResidentCard"],
+  "issuer": "did:example:489398593",
+  "identifier": "83627465",
+  "name": "Permanent Resident Card",
+  "description": "Government of Example Permanent Resident Card.",
+  "issuanceDate": "2019-12-03T12:19:52Z",
+  "expirationDate": "2029-12-03T12:19:52Z",
+  "credentialSubject": {
+    "type": ["PermanentResident", "Person"],
+    "givenName": "JOHN",
+    "familyName": "SMITH",
+    "gender": "Male",
+    "image": "data:image/png;base64,iVBORw0KGgokJggg==",
+    "residentSince": "2015-01-01",
+    "lprCategory": "C09",
+    "lprNumber": "999-999-999",
+    "commuterClassification": "C1",
+    "birthCountry": "Bahamas",
+    "birthDate": "1958-07-17"
+  }
+}

__tests__/__fixtures__/data/test_anonymous_vc_reveal_document.json

@@ -0,0 +1,17 @@
+{
+  "@context": [
+    "https://www.w3.org/2018/credentials/v1",
+    "https://w3id.org/citizenship/v1",
+    "https://w3id.org/security/v3-unstable"
+  ],
+  "type": ["VerifiableCredential", "PermanentResidentCard"],
+  "@explicit": true,
+  "issuer": {},
+  "name": {},
+  "description": {},
+  "credentialSubject": {
+    "type": ["PermanentResident", "Person"],
+    "@explicit": true,
+    "commuterClassification": {}
+  }
+}

__tests__/__fixtures__/data/test_nested_anonymous_vc_document.json

@@ -0,0 +1,18 @@
+{
+  "@context": [
+    "https://www.w3.org/2018/credentials/v1",
+    "https://www.w3.org/2018/credentials/examples/v1",
+    "https://www.w3id.org/security/v3-unstable"
+  ],
+  "type": ["VerifiableCredential", "UniversityDegreeCredential"],
+  "issuer": "did:example:489398593",
+  "issuanceDate": "2020-03-10T04:24:12.164Z",
+  "credentialSubject": {
+    "degree": {
+      "type": "BachelorDegree",
+      "name": "Bachelor of Science and Arts",
+      "degreeType": "Underwater Basket Weaving"
+    },
+    "college": "Contoso University"
+  }
+}

__tests__/__fixtures__/index.ts

@@ -36,6 +36,9 @@ import testNestedVcDocument from "./data/test_nested_vc_document.json";
 import testSignedNestedVcDocument from "./data/test_signed_nested_vc_document.json";
 import testProofNestedVcDocument from "./data/test_proof_nested_vc_document.json";
 import testPartialProofNestedVcDocument from "./data/test_partial_proof_nested_vc_document.json";
+import testAnonymousVcDocument from "./data/test_anonymous_vc.json";
+import testRevealAnonymousVcDocument from "./data/test_anonymous_vc_reveal_document.json";
+import testNestedAnonymousVcDocument from "./data/test_nested_anonymous_vc_document.json";
 
 export {
   exampleBls12381KeyPair,
@@ -61,5 +64,8 @@ export {
   testSignedNestedVcDocument,
   testProofNestedVcDocument,
   testPartialProofNestedVcDocument,
-  customLoader
+  customLoader,
+  testAnonymousVcDocument,
+  testRevealAnonymousVcDocument,
+  testNestedAnonymousVcDocument
 };

src/BbsBlsSignatureProof2020.ts

@@ -126,19 +126,8 @@ export class BbsBlsSignatureProof2020 extends suites.LinkedDataProof {
     // Transform any blank node identifiers for the input
     // document statements into actual node identifiers
     // e.g _:c14n0 => urn:bnid:_:c14n0
-    const transformedInputDocumentStatements = documentStatements.map(
-      element => {
-        if (element.includes("_:c14n")) {
-          const prefixIndex = element.indexOf("_:c14n");
-          const spaceIndex = element.indexOf(" ", prefixIndex);
-          return element.replace(
-            element.substring(prefixIndex, spaceIndex),
-            `<urn:bnid:${element.substring(prefixIndex, spaceIndex)}>`
-          );
-        }
-
-        return element;
-      }
+    const transformedInputDocumentStatements = documentStatements.map(element =>
+      element.replace(/(_:c14n[0-9]+)/g, "<urn:bnid:$1>")
     );
 
     //Transform the resulting RDF statements back into JSON-LD
@@ -263,18 +252,9 @@ export class BbsBlsSignatureProof2020 extends suites.LinkedDataProof {
 
       // Transform the blank node identifier placeholders for the document statements
       // back into actual blank node identifiers
-      const transformedDocumentStatements = documentStatements.map(element => {
-        const prefixString = "<urn:bnid:";
-        if (element.includes("<urn:bnid:_:c14n")) {
-          const prefixIndex = element.indexOf(prefixString);
-          const closingIndex = element.indexOf(">", prefixIndex);
-          return element.replace(
-            element.substring(prefixIndex, closingIndex + 1),
-            element.substring(prefixIndex + prefixString.length, closingIndex)
-          );
-        }
-        return element;
-      });
+      const transformedDocumentStatements = documentStatements.map(element =>
+        element.replace(/<urn:bnid:(_:c14n[0-9]+)>/g, "$1")
+      );
 
       // Combine all the statements to be verified
       const statementsToVerify: Uint8Array[] = proofStatements