Add support for compressed secp256k1 publicKey (#567)

* Add compressed SECP256K1 publicKey test for eciesSecp256k1Encrypt() Signed-off-by: Hiroaki KAWAI <[email protected]> * Add compressed SECP256K1 ephemeral publicKey support in encrypted message. Signed-off-by: Hiroaki KAWAI <[email protected]> * Convert SECP256K1 public key to compressed from uncompressed. Signed-off-by: Hiroaki KAWAI <[email protected]> * npm install; lint and formatting; remove isCompressed option * Nit --------- Signed-off-by: Hiroaki KAWAI <[email protected]> Co-authored-by: Diane Huxley <[email protected]>
decentralized-identity · Oct 20, 2023 · eb96cbc · eb96cbc
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diff --git a/README.md b/README.md
@@ -48,7 +48,7 @@ Here's to a thrilling Hacktoberfest voyage with us! 🎉
 # Decentralized Web Node (DWN) SDK <!-- omit in toc -->
 
 Code Coverage
-![Statements](https://img.shields.io/badge/statements-98.47%25-brightgreen.svg?style=flat) ![Branches](https://img.shields.io/badge/branches-95.61%25-brightgreen.svg?style=flat) ![Functions](https://img.shields.io/badge/functions-95.68%25-brightgreen.svg?style=flat) ![Lines](https://img.shields.io/badge/lines-98.47%25-brightgreen.svg?style=flat)
+![Statements](https://img.shields.io/badge/statements-98.47%25-brightgreen.svg?style=flat) ![Branches](https://img.shields.io/badge/branches-95.55%25-brightgreen.svg?style=flat) ![Functions](https://img.shields.io/badge/functions-95.7%25-brightgreen.svg?style=flat) ![Lines](https://img.shields.io/badge/lines-98.47%25-brightgreen.svg?style=flat)
 
 - [Introduction](#introduction)
 - [Installation](#installation)

diff --git a/package-lock.json b/package-lock.json
diff --git a/package.json b/package.json
@@ -72,7 +72,7 @@
     "ajv": "8.12.0",
     "blockstore-core": "4.2.0",
     "cross-fetch": "4.0.0",
-    "eciesjs": "0.4.0",
+    "eciesjs": "0.4.5",
     "flat": "5.0.2",
     "interface-blockstore": "5.2.3",
     "interface-store": "5.1.2",

diff --git a/src/utils/encryption.ts b/src/utils/encryption.ts
@@ -2,6 +2,9 @@ import * as crypto from 'crypto';
 import * as eciesjs from 'eciesjs';
 import { Readable } from 'readable-stream';
 
+// compress publicKey for message encryption
+eciesjs.ECIES_CONFIG.isEphemeralKeyCompressed = true;
+
 /**
  * Utility class for performing common, non-DWN specific encryption operations.
  */
@@ -67,18 +70,27 @@ export class Encryption {
    * with SECP256K1 for the asymmetric calculations, HKDF as the key-derivation function,
    * and AES-GCM for the symmetric encryption and MAC algorithms.
    */
-  public static async eciesSecp256k1Encrypt(uncompressedPublicKey: Uint8Array, plaintext: Uint8Array): Promise<EciesEncryptionOutput> {
+  public static async eciesSecp256k1Encrypt(publicKeyBytes: Uint8Array, plaintext: Uint8Array): Promise<EciesEncryptionOutput> {
     // underlying library requires Buffer as input
-    const publicKey = Buffer.from(uncompressedPublicKey);
+    const publicKey = Buffer.from(publicKeyBytes);
     const plaintextBuffer = Buffer.from(plaintext);
 
     const cryptogram = eciesjs.encrypt(publicKey, plaintextBuffer);
 
     // split cryptogram returned into constituent parts
-    const ephemeralPublicKey = cryptogram.subarray(0, 65);
-    const initializationVector = cryptogram.subarray(65, 81);
-    const messageAuthenticationCode = cryptogram.subarray(81, 97);
-    const ciphertext = cryptogram.subarray(97);
+    let start = 0;
+    let end = Encryption.isEphemeralKeyCompressed ? 33 : 65;
+    const ephemeralPublicKey = cryptogram.subarray(start, end);
+
+    start = end;
+    end += eciesjs.ECIES_CONFIG.symmetricNonceLength;
+    const initializationVector = cryptogram.subarray(start, end);
+
+    start = end;
+    end += 16; // eciesjs.consts.AEAD_TAG_LENGTH
+    const messageAuthenticationCode = cryptogram.subarray(start, end);
+
+    const ciphertext = cryptogram.subarray(end);
 
     return {
       ciphertext,
@@ -107,6 +119,13 @@ export class Encryption {
 
     return plaintext;
   }
+
+  /**
+   * Expose eciesjs library configuration
+   */
+  static get isEphemeralKeyCompressed():boolean {
+    return eciesjs.ECIES_CONFIG.isEphemeralKeyCompressed;
+  }
 }
 
 export type EciesEncryptionOutput = {

diff --git a/src/utils/secp256k1.ts b/src/utils/secp256k1.ts
@@ -67,15 +67,16 @@ export class Secp256k1 {
   }
 
   /**
-   * Creates a uncompressed key in raw bytes from the given SECP256K1 JWK.
+   * Creates a compressed key in raw bytes from the given SECP256K1 JWK.
    */
   public static publicJwkToBytes(publicJwk: PublicJwk): Uint8Array {
     const x = Encoder.base64UrlToBytes(publicJwk.x);
     const y = Encoder.base64UrlToBytes(publicJwk.y!);
 
-    // leading byte of 0x04 indicates that the public key is uncompressed
-    const publicKey = new Uint8Array([0x04, ...x, ...y]);
-    return publicKey;
+    return secp256k1.ProjectivePoint.fromAffine({
+      x : secp256k1.etc.bytesToNumberBE(x),
+      y : secp256k1.etc.bytesToNumberBE(y)
+    }).toRawBytes(true);
   }
 
   /**
@@ -129,20 +130,20 @@ export class Secp256k1 {
   }
 
   /**
-   * Generates key pair in raw bytes, where the `publicKey` is uncompressed.
+   * Generates key pair in raw bytes, where the `publicKey` is compressed.
    */
   public static async generateKeyPairRaw(): Promise<{publicKey: Uint8Array, privateKey: Uint8Array}> {
     const privateKey = secp256k1.utils.randomPrivateKey();
-    const publicKey = secp256k1.getPublicKey(privateKey, false); // `false` = uncompressed
+    const publicKey = secp256k1.getPublicKey(privateKey, true); // `true` = compressed
 
     return { publicKey, privateKey };
   }
 
   /**
-   * Gets the uncompressed public key of the given private key.
+   * Gets the compressed public key of the given private key.
    */
   public static async getPublicKey(privateKey: Uint8Array): Promise<Uint8Array> {
-    const publicKey = secp256k1.getPublicKey(privateKey, false); // `false` = uncompressed
+    const publicKey = secp256k1.getPublicKey(privateKey, true); // `true` = compressed
     return publicKey;
   }
 

diff --git a/tests/utils/encryption.spec.ts b/tests/utils/encryption.spec.ts
@@ -4,6 +4,7 @@ import { Encryption } from '../../src/utils/encryption.js';
 import { expect } from 'chai';
 import { Readable } from 'readable-stream';
 import { Secp256k1 } from '../../src/utils/secp256k1.js';
+import { etc as Secp256k1Etc } from '@noble/secp256k1';
 import { TestDataGenerator } from './test-data-generator.js';
 
 describe('Encryption', () => {
@@ -117,6 +118,21 @@ describe('Encryption', () => {
 
       expect(ArrayUtility.byteArraysEqual(originalPlaintext, decryptedPlaintext)).to.be.true;
     });
+
+    it('should be able to accept both compressed and uncompressed publicKeys', async () => {
+      const originalPlaintext = TestDataGenerator.randomBytes(32);
+      const h2b = Secp256k1Etc.hexToBytes;
+      // Following test vector was taken from @noble/secp256k1 test file.
+      // noble-secp256k1/main/test/vectors/secp256k1/privates.json
+      const privateKey = h2b('9c7fc36bc106fd7df5e1078d03e34b9a045892abdd053ec69bfeb22327529f6c');
+      const compressed = h2b('03936cb2bd56e681d360bbce6a3a7a1ccbf72f3ab8792edbc45fb08f55b929c588');
+      const uncompressed = h2b('04936cb2bd56e681d360bbce6a3a7a1ccbf72f3ab8792edbc45fb08f55b929c588529b8cee53f7eff1da5fc0e6050d952b37d4de5c3b85e952dfe9d9e9b2b3b6eb');
+      for (const publicKey of [compressed, uncompressed]) {
+        const encrypted = await Encryption.eciesSecp256k1Encrypt(publicKey, originalPlaintext);
+        const decrypted = await Encryption.eciesSecp256k1Decrypt({ privateKey, ...encrypted });
+        expect(ArrayUtility.byteArraysEqual(originalPlaintext, decrypted)).to.be.true;
+      }
+    });
   });
 });
 

diff --git a/tests/utils/secp256k1.spec.ts b/tests/utils/secp256k1.spec.ts
@@ -6,6 +6,13 @@ import { Secp256k1 } from '../../src/utils/secp256k1.js';
 import { TestDataGenerator } from './test-data-generator.js';
 
 describe('Secp256k1', () => {
+  describe('generateKeyPairRaw()', () => {
+    it('should generate compressed publicKey', async () => {
+      const { publicKey } = await Secp256k1.generateKeyPairRaw();
+      expect(publicKey.length).to.equal(33);
+    });
+  });
+
   describe('validateKey()', () => {
     it('should throw if key is not a valid SECP256K1 key', async () => {
       const validKey = (await Secp256k1.generateKeyPair()).publicJwk;