feat: implements convert mnemonic to privateKey (#64)

CHANGELOG.md

@@ -3,6 +3,8 @@
 ## Unreleased
 
 TBD
+- [\#64](https://github.com/medibloc/panacea-js/pull/64) feat: implement a function to convert a mnemonic to a secp256k1 private key
+
 
 ## [v2.0.1](https://github.com/medibloc/panacea-js/releases/tag/v2.0.1) - 2022-06-03
 

docs/examples.md

@@ -144,3 +144,16 @@ assertIsDeliverTxSuccess(result);
 const didDocumentWithSeq = await client.getPanaceaClient().getDid(didDocument.id);
 console.log(didDocumentWithSeq);
 ```
+
+## Convert mnemonic to Secp256k1 privateKey
+
+```ts
+import { Secp256k1 as CryptoSecp256k1, stringToPath } from "@cosmjs/crypto";
+import { Secp256k1 } from "./secp256k1";
+
+const mnemonic = "bulb rail ...";
+const hdPath = stringToPath("m/44'/371'/0'/0/0");
+
+const privateKey = await Secp256k1.parseMnemonicToPrivateKey(mnemonic, hdPath);
+const {pubkey} = await CryptoSecp256k1.makeKeypair(privateKey);
+```

src/crypto/secp256k1.spec.ts

@@ -0,0 +1,19 @@
+import { Secp256k1 as CryptoSecp256k1, stringToPath, sha256 } from "@cosmjs/crypto";
+import { panacead } from "../testutils";
+import { TextEncoder } from "util";
+import { Secp256k1 } from "./secp256k1";
+
+describe("Secp256k1", () => {
+
+  it("parseMnemonicToPrivateKey", async () => {
+    const body = "testBody";
+    const hashedBody = sha256(new TextEncoder().encode(body));
+    const hdPath = stringToPath("m/44'/371'/0'/0/0");
+
+    const privateKey = await Secp256k1.parseMnemonicToPrivateKey(panacead.mnemonic, hdPath);
+    const {pubkey} = await CryptoSecp256k1.makeKeypair(privateKey);
+
+    const signature = await CryptoSecp256k1.createSignature(hashedBody, privateKey)
+    expect(CryptoSecp256k1.verifySignature(signature, hashedBody, pubkey)).toBeTruthy()
+  });
+});

src/crypto/secp256k1.ts

@@ -1,5 +1,6 @@
 import ecc from "secp256k1";
 import { randomBytes } from "crypto";
+import { Bip39, EnglishMnemonic, Slip10, Slip10Curve, Slip10RawIndex } from "@cosmjs/crypto"
 
 export class Secp256k1 {
   static generatePrivateKey(): Uint8Array {
@@ -17,4 +18,10 @@ export class Secp256k1 {
   static sign(data32: Uint8Array, privKey: Uint8Array): Uint8Array {
     return ecc.ecdsaSign(data32, privKey).signature;
   }
+
+  static async parseMnemonicToPrivateKey(mnemonic: string, hdPath: readonly Slip10RawIndex[]): Promise<Uint8Array> {
+    const mnemonicChecked = new EnglishMnemonic(mnemonic);
+    const seed = await Bip39.mnemonicToSeed(mnemonicChecked, "");
+    return Slip10.derivePath(Slip10Curve.Secp256k1, seed, hdPath).privkey;
+  }
 }