add additional verification to vaultformat 8 module

frontend/src/common/jwt.ts

@@ -7,6 +7,16 @@ export type JWTHeader = {
 }
 
 export class JWT {
+  public header: any;
+  public payload: any;
+  public signature: Uint8Array;
+
+  private constructor(header: any, payload: any, signature: Uint8Array) {
+    this.header = header;
+    this.payload = payload;
+    this.signature = signature;
+  }
+
   /**
    * Creates a ES384 JWT (signed with ECDSA using P-384 and SHA-384).
    * 
@@ -37,4 +47,16 @@ export class JWT {
     );
     return base64url.stringify(new Uint8Array(signature), { pad: false });
   }
+
+  public static async parse(token: string): Promise<JWT> {
+    const jwtSections = token.split('.');
+    if (jwtSections.length != 3 || !jwtSections[0] || !jwtSections[1] || !jwtSections[2]) {
+      throw new Error('Invalid JWT');
+    }
+
+    const header = JSON.parse(new TextDecoder().decode(base64url.parse(jwtSections[0], { loose: true })));
+    const payload = JSON.parse(new TextDecoder().decode(base64url.parse(jwtSections[1], { loose: true })));
+    const signature = base64url.parse(jwtSections[2], { loose: true });
+    return new JWT(header, payload, signature);
+  }
 }

frontend/src/common/vaultFormat8.ts

@@ -5,6 +5,7 @@ import { VaultDto } from './backend';
 import config, { absFrontendBaseURL } from './config';
 import { AccessTokenProducing, GCM_NONCE_LEN, OtherVaultMember, UnwrapKeyError, UserKeys, VaultTemplateProducing } from './crypto';
 import { CRC32, wordEncoder } from './util';
+import { JWT } from './jwt';
 
 interface VaultConfigPayload {
   jti: string
@@ -138,13 +139,40 @@ export class VaultFormat8 implements AccessTokenProducing, VaultTemplateProducin
     }
   }
 
+  public static async verifyAndRecover(vaultMetadataToken: string, recoveryKey: string) {
+    //basic validation
+    const vaultMetadata = JWT.parse(vaultMetadataToken);
+
+    const sigSeparatorIndex = vaultMetadataToken.lastIndexOf('.');
+    const headerPlusPayload = vaultMetadataToken.slice(0,sigSeparatorIndex);
+    const signature = vaultMetadataToken.slice(sigSeparatorIndex + 1,vaultMetadataToken.length);
+
+    const message = new TextEncoder().encode(headerPlusPayload);
+    const key = await this.transcodeKey(recoveryKey);
+    var digest = await crypto.subtle.sign(
+      VaultFormat8.MASTERKEY_KEY_DESIGNATION,
+      key,
+      message
+    );
+    const base64urlDigest = base64url.stringify(new Uint8Array(digest), { pad: false });
+    if (!(signature === base64urlDigest)) {
+      throw new Error('Verification failed.');
+    }
+
+    return new VaultFormat8(key);
+  }
+
   /**
    * Restore the master key from a given recovery key, create a new admin signature key pair.
    * @param recoveryKey The recovery key
    * @returns The recovered master key
    * @throws Error, if passing a malformed recovery key
    */
   public static async recover(recoveryKey: string): Promise<VaultFormat8> {
+    return new VaultFormat8(await this.transcodeKey(recoveryKey));
+  }
+
+  public static async transcodeKey(recoveryKey: string): Promise<CryptoKey> {
     // decode and check recovery key:
     const decoded = wordEncoder.decode(recoveryKey);
     if (decoded.length !== 66) {
@@ -158,14 +186,13 @@ export class VaultFormat8 implements AccessTokenProducing, VaultTemplateProducin
     }
 
     // construct new VaultKeys from recovered key
-    const key = crypto.subtle.importKey(
+    return crypto.subtle.importKey(
       'raw',
       decodedKey,
       VaultFormat8.MASTERKEY_KEY_DESIGNATION,
       true,
       ['sign']
     );
-    return new VaultFormat8(await key);
   }
 
   /** @inheritdoc */

frontend/test/common/vaultFormat8.spec.ts

@@ -87,6 +87,19 @@ describe('Vault Format 8', () => {
     ]);
   });
 
+  it('verifyAndRecover() succeeds for key and corresponding metadata', async () => {
+    const recoveryKey = `
+      exotic ghost cooperate rain writing purple bicycle fixed first elite treaty friendly screen pull middle seventeen passport
+      correctly bored remains give profound ultimate charm haunt retired viable ray delegate indicator race cause aluminium
+      obesity site tactical root rumour theology glory consist comic terribly substance
+      `;
+    const vaultMetadata = 'eyJraWQiOiJtYXN0ZXJrZXlmaWxlOm1hc3RlcmtleS5jcnlwdG9tYXRvciIsInR5cCI6IkpXVCIsImFsZyI6IkhTMjU2In0.eyJmb3JtYXQiOjgsInNob3J0ZW5pbmdUaHJlc2hvbGQiOjIyMCwianRpIjoiZmI0N2IyMDYtM2FjMS00Y2RkLThkNTMtYWE0OWM4NjY4Nzk5IiwiY2lwaGVyQ29tYm8iOiJTSVZfQ1RSTUFDIn0.oSMdTtcC6LtoC37knQpNoPo3biUNFCRfxownXIFf_GM';
+
+    const recovered = await VaultFormat8.verifyAndRecover(vaultMetadata, recoveryKey);
+    const recoveredKey = await crypto.subtle.exportKey('jwk', recovered.masterKey);
+    //TODO: expect(recoveredKey.k).to.eq('VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV3d3d3d3d3d3d3d3d3d3d3d3d3d3d3d3d3d3d3d3d3dw');
+  });
+
   it('encryptForUser()', async () => {
     const encrypted = await testVault.encryptForUser(alice.keyPair.publicKey);