Function nip44Encrypt

src/utils/nip44.ts:97–110

(plaintext: string, conversationKey: Buffer, nonce: Buffer = randomBytes(32))

 * Output format: base64(0x02 || nonce[32] || ciphertext || mac[32])
 */
export function nip44Encrypt(plaintext: string, conversationKey: Buffer, nonce: Buffer = randomBytes(32)): string {
  const { chachaKey, chachaNonce, hmacKey } = getMessageKeys(conversationKey, nonce)
  const padded = pad(plaintext)

  // ChaCha20: OpenSSL expects a 16-byte IV = [counter_le32=0][nonce_96bit]
  const iv = Buffer.concat([Buffer.alloc(4), chachaNonce])
  const cipher = createCipheriv('chacha20', chachaKey, iv)
  const ciphertext = Buffer.concat([cipher.update(padded), cipher.final()])

  // MAC = HMAC-SHA256(hmacKey, nonce || ciphertext)
  const mac = createHmac('sha256', hmacKey).update(nonce).update(ciphertext).digest()

  return Buffer.concat([Buffer.from([0x02]), nonce, ciphertext, mac]).toString('base64')
}

/**
 * Decrypt a NIP-44 v2 payload.