bcrypt — go-ruby-bcrypt

A pure-Go (no cgo) reimplementation of Ruby's bcrypt gem — BCrypt::Password and BCrypt::Engine — for hashing and verifying passwords with the OpenBSD bcrypt() algorithm. It produces and consumes the same $2a$ hashes the gem does, so a hash created here verifies under the gem's Password#== and a gem-created hash verifies here — without any Ruby runtime.

It is the password-hashing backend for go-embedded-ruby, but is a standalone, reusable module — a sibling of go-ruby-yaml (the Psych port), go-ruby-regexp (the Onigmo engine) and go-ruby-erb (the ERB compiler).

Cross-compatible with the gem, both directions

The crypto core is the OpenBSD bcrypt key schedule over golang.org/x/crypto/blowfish; there is no cgo and no C bcrypt.

• Our hash → gem. Create emits a $2a$NN$… hash the gem's BCrypt::Password.new(hash) == secret accepts.
• Gem hash → us. NewPassword(gemHash).EqualString(secret) accepts a hash the gem produced.
• 72-byte truncation. The gem truncates secrets to 72 bytes before hashing (staying compatible with the older C library). This port truncates identically, so a secret longer than 72 bytes hashes to the same value here and in the gem and cross-verifies at the edge in both directions.

Features

Faithful port of the gem's public surface, validated against the bcrypt gem on every platform that has it:

• Password — Create / CreateString (default cost 12, $2a$), NewPassword, constant-time Equal / EqualString, and Cost / Salt / Version / Checksum / String accessors, matching BCrypt::Password.
• Engine — HashSecret, GenerateSalt(cost), ValidSecret, ValidSalt, ValidHash, AutodetectCost, and the MinCost / MaxCost / DefaultCost / MaxSecretBytesize / MaxSaltLength bounds, matching BCrypt::Engine.
• Gem-faithful cost handling — a cost below MinCost (4) is raised to 4, a cost of 0 or below is rejected (ErrInvalidCost), and a cost above MaxCost (31) is rejected (ErrCostTooHigh, the gem's ArgumentError).
• Errors — sentinel errors mirroring BCrypt::Errors (ErrInvalidSecret, ErrInvalidCost, ErrInvalidSalt, ErrInvalidHash), matchable with errors.Is.

CGO-free, 100% test coverage, gofmt + go vet clean, and green across the six 64-bit Go targets (amd64, arm64, riscv64, loong64, ppc64le, s390x).

Install

go get github.com/go-ruby-bcrypt/bcrypt

Usage

package main

import (
	"fmt"

	"github.com/go-ruby-bcrypt/bcrypt"
)

func main() {
	// Hash a secret (default cost 12; WithCost overrides).
	pw, _ := bcrypt.CreateString("my grand secret", bcrypt.WithCost(12))
	fmt.Println(pw.String()) // $2a$12$C5.FIvVDS9W4AYZ/Ib37Yu…

	// Verify, in constant time.
	fmt.Println(pw.EqualString("my grand secret")) // true
	fmt.Println(pw.EqualString("a paltry guess"))  // false

	// Parse a stored hash back.
	stored, _ := bcrypt.NewPassword(pw.String())
	fmt.Println(stored.Cost(), stored.Version()) // 12 2a
	fmt.Println(stored.Salt())                   // $2a$12$C5.FIvVDS9W4AYZ/Ib37Yu

	// Low-level engine: hash a secret against a specific salt.
	salt, _ := bcrypt.GenerateSalt(10)
	h, _ := bcrypt.HashSecret([]byte("secret"), salt)
	fmt.Println(h)
}

API

// Password (BCrypt::Password)
func Create(secret []byte, opts ...CreateOption) (*Password, error)
func CreateString(secret string, opts ...CreateOption) (*Password, error)
func NewPassword(rawHash string) (*Password, error)
func WithCost(cost int) CreateOption

func (p *Password) Equal(secret []byte) bool
func (p *Password) EqualString(secret string) bool
func (p *Password) String() string   // to_s
func (p *Password) Version() string  // "2a"
func (p *Password) Cost() int
func (p *Password) Salt() string
func (p *Password) Checksum() string

// Engine (BCrypt::Engine)
func HashSecret(secret []byte, salt string) (string, error)
func GenerateSalt(cost int) (string, error)
func ValidSecret(secret []byte) bool
func ValidSalt(salt string) bool
func ValidHash(h string) bool
func AutodetectCost(salt string) int

const (
	DefaultCost       = 12 // DEFAULT_COST
	MinCost           = 4  // MIN_COST
	MaxCost           = 31 // MAX_COST
	MaxSecretBytesize = 72 // MAX_SECRET_BYTESIZE
	MaxSaltLength     = 16 // MAX_SALT_LENGTH
)

// Errors (BCrypt::Errors), matchable with errors.Is.
var ErrInvalidSecret, ErrInvalidCost, ErrInvalidSalt, ErrInvalidHash, ErrCostTooHigh error

Tests & coverage

The suite pairs deterministic, ruby-free golden vectors (fixed salt + secret → hash, captured from the gem; these alone hold coverage at 100%, so the qemu cross-arch and Windows lanes pass the gate) with a differential gem oracle gated on RUBY_VERSION >= "4.0": hashes made here are verified by the gem's Password#==, gem-made hashes are verified here, .cost / .salt / .version / .checksum parsing is compared against the gem, and the 72-byte truncation edge is crossed in both directions. The oracle scripts $stdout.binmode so Windows text-mode never pollutes the bytes, and skip themselves where ruby or the gem is absent.

COVERPKG=$(go list ./... | paste -sd, -)
go test -race -coverpkg="$COVERPKG" -coverprofile=cover.out ./...
go tool cover -func=cover.out | tail -1   # 100.0%

License

BSD-3-Clause — see LICENSE. Copyright the go-ruby-bcrypt/bcrypt authors.

WebAssembly

Being pure Go (CGO=0), this library also compiles to WebAssembly — both GOOS=js GOARCH=wasm (browser / Node.js) and GOOS=wasip1 GOARCH=wasm (WASI). CI builds both targets on every push, alongside the six 64-bit native/qemu arches.

GOOS=js     GOARCH=wasm go build ./...   # browser / Node
GOOS=wasip1 GOARCH=wasm go build ./...   # WASI (wasmtime, wasmer, wasmedge, …)