passlib for go

Python's passlib is quite an amazing library. I'm not sure there's a password library in existence with more thought put into it, or with more support for obscure password formats.

This is a skeleton of a port of passlib to Go. It dogmatically adopts the modular crypt format, which passlib has excellent documentation for.

Currently, it supports:

  • Argon2i
  • scrypt-sha256
  • sha512-crypt
  • sha256-crypt
  • bcrypt
  • passlib's bcrypt-sha256 variant
  • pbkdf2-sha512 (in passlib format)
  • pbkdf2-sha256 (in passlib format)
  • pbkdf2-sha1 (in passlib format)

By default, it will hash using scrypt-sha256 and verify existing hashes using any of these schemes.

Example Usage

There's a default context for ease of use. Most people need only concern themselves with the functions Hash and Verify:

// Hash a plaintext, UTF-8 password.
func Hash(password string) (hash string, err error)

// Verifies a plaintext, UTF-8 password using a previously derived hash.
// Returns non-nil err if verification fails.
// Also returns an upgraded password hash if the hash provided is
// deprecated.
func Verify(password, hash string) (newHash string, err error)

Here's a rough skeleton of typical usage.

import ""

func RegisterUser() {

  password := get a (UTF-8, plaintext) password from somewhere

  hash, err := passlib.Hash(password)
  if err != nil {
    // couldn't hash password for some reason

  (store hash in database, etc.)

func CheckPassword() bool {
  password := get the password the user entered
  hash := the hash you stored from the call to Hash()

  newHash, err := passlib.Verify(password, hash)
  if err != nil {
    // incorrect password, malformed hash, etc.
    // either way, reject
    return false

  // The context has decided, as per its policy, that
  // the hash which was used to validate the password
  // should be changed. It has upgraded the hash using
  // the verified password.
  if newHash != "" {
    (store newHash in database, replacing old hash)

  return true

scrypt Modular Crypt Format

Since scrypt does not have a pre-existing modular crypt format standard, I made one. It's as follows:


...where N, r and p are the respective difficulty parameters to scrypt as positive decimal integers without leading zeroes, and salt and hash are base64-encoded binary strings. Note that the RFC 4648 base64 encoding is used (not the one used by sha256-crypt and sha512-crypt).


passlib is partially derived from Python's passlib and so maintains its BSD license.

© 2008-2012 Assurance Technologies LLC.  (Python passlib)  BSD License
© 2014 Hugo Landau <[email protected]>  BSD License