packages/next/src/server/crypto-utils.ts

import crypto from 'crypto'

// Background:
// https://security.stackexchange.com/questions/184305/why-would-i-ever-use-aes-256-cbc-if-aes-256-gcm-is-more-secure

const CIPHER_ALGORITHM = `aes-256-gcm`,
  CIPHER_KEY_LENGTH = 32, // https://stackoverflow.com/a/28307668/4397028
  CIPHER_IV_LENGTH = 16, // https://stackoverflow.com/a/28307668/4397028
  CIPHER_TAG_LENGTH = 16,
  CIPHER_SALT_LENGTH = 64

const PBKDF2_ITERATIONS = 100_000 // https://support.1password.com/pbkdf2/

export function encryptWithSecret(secret: Buffer, data: string): string {
  const iv = crypto.randomBytes(CIPHER_IV_LENGTH)
  const salt = crypto.randomBytes(CIPHER_SALT_LENGTH)

  // https://nodejs.org/api/crypto.html#crypto_crypto_pbkdf2sync_password_salt_iterations_keylen_digest
  const key = crypto.pbkdf2Sync(
    secret,
    salt,
    PBKDF2_ITERATIONS,
    CIPHER_KEY_LENGTH,
    `sha512`
  )

  const cipher = crypto.createCipheriv(CIPHER_ALGORITHM, key, iv)
  const encrypted = Buffer.concat([cipher.update(data, `utf8`), cipher.final()])

  // https://nodejs.org/api/crypto.html#crypto_cipher_getauthtag
  const tag = cipher.getAuthTag()

  return Buffer.concat([
    // Data as required by:
    // Salt for Key: https://nodejs.org/api/crypto.html#crypto_crypto_pbkdf2sync_password_salt_iterations_keylen_digest
    // IV: https://nodejs.org/api/crypto.html#crypto_class_decipher
    // Tag: https://nodejs.org/api/crypto.html#crypto_decipher_setauthtag_buffer
    salt,
    iv,
    tag,
    encrypted,
  ]).toString(`hex`)
}

export function decryptWithSecret(
  secret: Buffer,
  encryptedData: string
): string {
  const buffer = Buffer.from(encryptedData, `hex`)

  const salt = buffer.slice(0, CIPHER_SALT_LENGTH)
  const iv = buffer.slice(
    CIPHER_SALT_LENGTH,
    CIPHER_SALT_LENGTH + CIPHER_IV_LENGTH
  )
  const tag = buffer.slice(
    CIPHER_SALT_LENGTH + CIPHER_IV_LENGTH,
    CIPHER_SALT_LENGTH + CIPHER_IV_LENGTH + CIPHER_TAG_LENGTH
  )
  const encrypted = buffer.slice(
    CIPHER_SALT_LENGTH + CIPHER_IV_LENGTH + CIPHER_TAG_LENGTH
  )

  // https://nodejs.org/api/crypto.html#crypto_crypto_pbkdf2sync_password_salt_iterations_keylen_digest
  const key = crypto.pbkdf2Sync(
    secret,
    salt,
    PBKDF2_ITERATIONS,
    CIPHER_KEY_LENGTH,
    `sha512`
  )

  const decipher = crypto.createDecipheriv(CIPHER_ALGORITHM, key, iv)
  decipher.setAuthTag(tag)

  return decipher.update(encrypted) + decipher.final(`utf8`)
}