go-hmaccrypt provides very strong password digests using a combination of a
peppered hash-based message authentication code (HMAC) and a salted adaptive
key derivation function like bcrypt.

A digest of each password is generated using e.g. HMAC-SHA512 with a pepper--a
value stored separately from the final digests--after which a bcrypt digest
of the HMAC digest is generated. The bcrypt digest is saved in e.g. a database.

With this approach, you can ensure the safety of user passwords even if an
SQL injection compromises the contents of your database's users table, or if
a weakness is found in e.g. bcrypt.

This approach is described on
https://wiki.mozilla.org/WebAppSec/Secure_Coding_Guidelines#Password_Storage

go-hmaccrypt can be used safely by multiple goroutines.

== Installation

go get github.com/pmylund/go-hmaccrypt

== Documentation

go doc github.com/pmylund/go-hmaccrypt
or http://go.pkgdoc.org/github.com/pmylund/go-hmaccrypt

== Usage

import (
	"crypto/sha512"
	"github.com/pmylund/go-hmaccrypt"
)

pepper := []byte("randomly generated sequence stored on disk or in the source")
crypt := hmaccrypt.New(sha512.New, pepper)

password := []byte("f00b4r!")
digest, err := crypt.Bcrypt(password, 10)
if err != nil {
	...
}
// save the bcrypt digest in the database

if err := crypt.BcryptCompare(digest, password); err == nil {
	// the password is a match
	...
}