NIP-06: Support multiple account private keys derived from seed words (#219)

Co-authored-by: fiatjaf_ <fiatjaf@gmail.com>

nip06.test.ts

@@ -6,9 +6,26 @@ test('generate private key from a mnemonic', async () => {
   expect(privateKey).toEqual('c26cf31d8ba425b555ca27d00ca71b5008004f2f662470f8c8131822ec129fe2')
 })
 
+test('generate private key for account 1 from a mnemonic', async () => {
+  const mnemonic = 'zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong'
+  const privateKey = privateKeyFromSeedWords(mnemonic, undefined, 1)
+  expect(privateKey).toEqual(
+    'b5fc7f229de3fb5c189063e3b3fc6c921d8f4366cff5bd31c6f063493665eb2b'
+  )
+})
+
 test('generate private key from a mnemonic and passphrase', async () => {
   const mnemonic = 'zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong'
   const passphrase = '123'
   const privateKey = privateKeyFromSeedWords(mnemonic, passphrase)
   expect(privateKey).toEqual('55a22b8203273d0aaf24c22c8fbe99608e70c524b17265641074281c8b978ae4')
 })
+
+test('generate private key for account 1 from a mnemonic and passphrase', async () => {
+  const mnemonic = 'zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong'
+  const passphrase = '123'
+  const privateKey = privateKeyFromSeedWords(mnemonic, passphrase, 1)
+  expect(privateKey).toEqual(
+    '2e0f7bd9e3c3ebcdff1a90fb49c913477e7c055eba1a415d571b6a8c714c7135'
+  )
+})

nip06.ts

@@ -3,9 +3,13 @@ import { wordlist } from '@scure/bip39/wordlists/english'
 import { generateMnemonic, mnemonicToSeedSync, validateMnemonic } from '@scure/bip39'
 import { HDKey } from '@scure/bip32'
 
-export function privateKeyFromSeedWords(mnemonic: string, passphrase?: string): string {
+export function privateKeyFromSeedWords(
+  mnemonic: string,
+  passphrase?: string,
+  accountIndex = 0
+): string {
   let root = HDKey.fromMasterSeed(mnemonicToSeedSync(mnemonic, passphrase))
-  let privateKey = root.derive(`m/44'/1237'/0'/0/0`).privateKey
+  let privateKey = root.derive(`m/44'/1237'/${accountIndex}'/0/0`).privateKey
   if (!privateKey) throw new Error('could not derive private key')
   return bytesToHex(privateKey)
 }