Password hashing and verification with Argon2id

main.go

package main

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"errors"
	"fmt"
	"log"
	"strings"

	"golang.org/x/crypto/argon2"
)

var (
	ErrInvalidHash         = errors.New("the encoded hash is not in the correct format")
	ErrIncompatibleVersion = errors.New("incompatible version of argon2")
)

type params struct {
	memory      uint32
	iterations  uint32
	parallelism uint8
	saltLength  uint32
	keyLength   uint32
}

func main() {
	p := &params{
		memory:      64 * 1024,
		iterations:  3,
		parallelism: 2,
		saltLength:  16,
		keyLength:   32,
	}

	encodedHash, err := generateFromPassword("password123", p)
	if err != nil {
		log.Fatal(err)
	}

	match, err := comparePasswordAndHash("pa$$word", encodedHash)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Match: %v\n", match)
}

func generateFromPassword(password string, p *params) (encodedHash string, err error) {
	// Generate a cryptographically secure random salt.
	salt, err := generateRandomBytes(p.saltLength)
	if err != nil {
		return "", err
	}

	// Pass the plaintext password, salt and parameters to the argon2.IDKey
	// function. This will generate a hash of the password using the Argon2id
	// variant.
	hash := argon2.IDKey([]byte(password), salt, p.iterations, p.memory, p.parallelism, p.keyLength)

	// Base64 encode the salt and hashed password.
	b64Salt := base64.RawStdEncoding.EncodeToString(salt)
	b64Hash := base64.RawStdEncoding.EncodeToString(hash)

	// Return a string using the standard encoded hash representation.
	encodedHash = fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s", argon2.Version, p.memory, p.iterations, p.parallelism, b64Salt, b64Hash)

	return encodedHash, nil
}

func generateRandomBytes(n uint32) ([]byte, error) {
	b := make([]byte, n)
	_, err := rand.Read(b)
	if err != nil {
		return nil, err
	}

	return b, nil
}

func comparePasswordAndHash(password, encodedHash string) (match bool, err error) {
	// Extract the parameters, salt and derived key from the encoded password
	// hash.
	p, salt, hash, err := decodeHash(encodedHash)
	if err != nil {
		return false, err
	}

	// Derive the key from the other password using the same parameters.
	otherHash := argon2.IDKey([]byte(password), salt, p.iterations, p.memory, p.parallelism, p.keyLength)

	// Check that the contents of the hashed passwords are identical. Note
	// that we are using the subtle.ConstantTimeCompare() function for this
	// to help prevent timing attacks.
	if subtle.ConstantTimeCompare(hash, otherHash) == 1 {
		return true, nil
	}
	return false, nil
}

func decodeHash(encodedHash string) (p *params, salt, hash []byte, err error) {
	vals := strings.Split(encodedHash, "$")
	if len(vals) != 6 {
		return nil, nil, nil, ErrInvalidHash
	}

	var version int
	_, err = fmt.Sscanf(vals[2], "v=%d", &version)
	if err != nil {
		return nil, nil, nil, err
	}
	if version != argon2.Version {
		return nil, nil, nil, ErrIncompatibleVersion
	}

	p = &params{}
	_, err = fmt.Sscanf(vals[3], "m=%d,t=%d,p=%d", &p.memory, &p.iterations, &p.parallelism)
	if err != nil {
		return nil, nil, nil, err
	}

	salt, err = base64.RawStdEncoding.Strict().DecodeString(vals[4])
	if err != nil {
		return nil, nil, nil, err
	}
	p.saltLength = uint32(len(salt))

	hash, err = base64.RawStdEncoding.Strict().DecodeString(vals[5])
	if err != nil {
		return nil, nil, nil, err
	}
	p.keyLength = uint32(len(hash))

	return p, salt, hash, nil
}

Just a minor refactor but you could replace lines 96-99 with:

return subtle.ConstantTimeCompare(hash, otherHash) == 1, nil

Hi!
How about to use argon2.Key() instead of argon2.IDKey()?
Seems like argon2i more suitable for server side password hashing and argon2id is more relevant to "proof-of-work" checks.

@AleksandrMakarenkov my understanding is that 2i should be preferred to 2d for password hashing --- not necessarily preferred to 2id. Using 2id is arguably better than just 2i in most cases as it provides some resistance to TMTO attacks.

@alexedwards Hey!
You were right :D
After investigating some posts i realized that argon2id is recommended as "primary algo" for most cases.
Here the link, https://crypto.stackexchange.com/questions/48935/why-use-argon2i-or-argon2d-if-argon2id-exists,
i hope it helps someone else!

great blog post, thank you