Added functionality to work with extended keys

src/constants.ts

@@ -1,3 +1,3 @@
 export const PUBLIC_KEY_PREFIX = 'npub'
 export const SECRET_KEY_PREFIX = 'nsec'
-export const DERIVATION_PATH = `m/44'/1237'/0'/0/0`
+export const DERIVATION_PATH = `m/44'/1237'`

src/index.ts

@@ -17,7 +17,7 @@ export function privateKeyFromSeedWords(
   }: { mnemonic: string, passphrase?: string }
 ): { privateKey: string } {
   const root = HDKey.fromMasterSeed(mnemonicToSeedSync(mnemonic, passphrase))
-  const { privateKey } = root.derive(DERIVATION_PATH)
+  const { privateKey } = root.derive(`${DERIVATION_PATH}/0'/0/0`)
   if (!privateKey) {
     throw new Error('could not derive private key')
   }
@@ -55,6 +55,40 @@ export function getBech32PublicKey({ publicKey }: { publicKey: string }): { bech
   }
 }
 
+export function extendedPairFromSeedWords(mnemonic: string, passphrase?: string, extendedAccountIndex = 0): {
+  privateExtendedKey: string,
+  publicExtendedKey: string
+} {
+  let root = HDKey.fromMasterSeed(mnemonicToSeedSync(mnemonic, passphrase))
+  let seed = root.derive(`${DERIVATION_PATH}/${extendedAccountIndex}'`)
+  let privateExtendedKey = seed.privateExtendedKey
+  let publicExtendedKey = seed.publicExtendedKey
+  if (!privateExtendedKey) throw new Error('could not derive private extended key')
+  return { privateExtendedKey, publicExtendedKey }
+}
+
+export function accountFromExtendedKey(base58key: string, accountIndex = 0): {
+  privateKey?: { hex: string, bech32: string },
+  publicKey:  { hex: string, bech32: string }
+} {
+  let extendedKey = HDKey.fromExtendedKey(base58key)
+  let version = base58key.slice(0, 4)
+  let child = extendedKey.deriveChild(0).deriveChild(accountIndex)
+  let publicKeyHex = bytesToHex(child.publicKey!.slice(1))
+  if (!publicKeyHex) throw new Error('could not derive public key')
+  let publicKeyBech32 = hexToBech32(publicKeyHex, 'npub')
+  if (version === 'xprv') {
+    let privateKeyHex = bytesToHex(child.privateKey!)
+    if (!privateKeyHex) throw new Error('could not derive private key')
+    let privateKeyBech32 = hexToBech32(privateKeyHex, 'nsec')
+    return { 
+      privateKey: { hex: privateKeyHex, bech32: privateKeyBech32 },
+      publicKey: { hex: publicKeyHex, bech32: publicKeyBech32 } 
+    } 
+  }
+  return { publicKey: { hex: publicKeyHex, bech32: publicKeyBech32 } } 
+}
+
 export function generateSeedWords(): { mnemonic: string } {
   return {
     mnemonic: generateMnemonic(wordlist)

tests/accountFromExtendedKey.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from 'vitest'
+import { accountFromExtendedKey } from '../src/index'
+
+describe('accountFromExtendedKey', () => {
+  it('should get account from extended private key', () => {
+    const { privateKey, publicKey } = accountFromExtendedKey('xprv9z78fizET65qsCaRr1MSutTSGk1fcKfSt1sBqmuWShtkjRJJ4WCKcSnha6EmgNzFSsyom3MWtydHyPtJtSLZQUtictVQtM2vkPcguh6TQCH')
+
+    expect(privateKey?.hex).toBe('5f29af3b9676180290e77a4efad265c4c2ff28a5302461f73597fda26bb25731')
+    expect(privateKey?.bech32).toBe('nsec1tu567wukwcvq9y880f8045n9cnp07299xqjxrae4jl76y6aj2ucs2mkupq')
+    expect(publicKey.hex).toBe('e8bcf3823669444d0b49ad45d65088635d9fd8500a75b5f20b59abefa56a144f')
+    expect(publicKey.bech32).toBe('npub1az708q3kd9zy6z6f44zav5ygvdwelkzspf6mtusttx47lft2z38sghk0w7')
+  })
+
+  it('should get account from extended public key', () => {
+    const { privateKey, publicKey } = accountFromExtendedKey('xpub6D6V5EX8HTe95getx2tTH2QApmrA1nPJFEnneAK813RjcDdSc3WaAF7BRNpTF7o7zXjVm3DD3VMX66jhQ7wLaZ9sS6NzyfiwfzqDZbxvpDN')
+
+    expect(publicKey.hex).toBe('e8bcf3823669444d0b49ad45d65088635d9fd8500a75b5f20b59abefa56a144f')
+    expect(publicKey.bech32).toBe('npub1az708q3kd9zy6z6f44zav5ygvdwelkzspf6mtusttx47lft2z38sghk0w7')
+  })
+})

tests/extendedPairFromSeedWords.test.ts

@@ -0,0 +1,11 @@
+import { describe, expect, it } from 'vitest'
+import { extendedPairFromSeedWords } from '../src/index'
+
+describe('extendedPairFromSeedWords', () => {
+  it('should get extended keys pair from mnemonic', () => {
+    const { privateExtendedKey, publicExtendedKey } = extendedPairFromSeedWords('abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about')
+
+    expect(privateExtendedKey).toBe('xprv9z78fizET65qsCaRr1MSutTSGk1fcKfSt1sBqmuWShtkjRJJ4WCKcSnha6EmgNzFSsyom3MWtydHyPtJtSLZQUtictVQtM2vkPcguh6TQCH')
+    expect(publicExtendedKey).toBe('xpub6D6V5EX8HTe95getx2tTH2QApmrA1nPJFEnneAK813RjcDdSc3WaAF7BRNpTF7o7zXjVm3DD3VMX66jhQ7wLaZ9sS6NzyfiwfzqDZbxvpDN')
+  })
+})

tests/privateKeyFromSeedWords.test.ts

@@ -4,7 +4,7 @@ import { DERIVATION_PATH } from '../src/constants'
 
 describe('privateKeyFromSeedWords', () => {
   it('should use the NIP-06 derivation path', () => {
-    expect(DERIVATION_PATH).toBe(`m/44'/1237'/0'/0/0`)
+    expect(`${DERIVATION_PATH}/0'/0/0`).toBe(`m/44'/1237'/0'/0/0`)
   })
 
   it('should get a 64 bytes hex private key from mnemonic', () => {