go-passwd

Its a multi password type checker. Using the PHC string format we can identify a password hashing format from the prefix $name$ and then dispatch the hashing or checking to its specific format.

Example

Here is an example of usage:

// Example of upgrading password hash to a greater complexity.
//
// Note: This example uses very unsecure hash functions to allow for predictable output. Use of argon2.Argon2id or scrypt.Scrypt2 for greater hash security is recommended.
func Example() {
	pass := []byte("my_pass")
	hash := []byte("$1$81ed91e1131a3a5a50d8a68e8ef85fa0")

	pwd := passwd.New(
		argon2.Argon2id, // first is preferred type.
		&unix.MD5{},
	)

	_, err := pwd.Passwd(pass, hash)
	if err != nil {
		fmt.Println("fail: ", err)
		return
	}

	// Check if we want to update.
	if !pwd.IsPreferred(hash) {
		newHash, err := pwd.Passwd(pass, nil)
		if err != nil {
			fmt.Println("fail: ", err)
			return
		}

		fmt.Println("new hash:", string(newHash)[:31], "...")
	}

	// Output:
	//  new hash: $argon2id$v=19,m=65536,t=1,p=4$ ...
}

https://github.com/sour-is/go-passwd/blob/main/passwd_test.go#L40-L68

This shows how one would set a preferred hashing type and if the current version of ones password is not the preferred type updates it to enhance the security of the hashed password when someone logs in.

Fallthrough

Hold up now, that example hash doesn’t have a $ prefix!

Well for this there is the option for a hash type to set itself as a fall through if a matching hash doesn’t exist. This is good for legacy password types that don’t follow the convention.

func (p *plainPasswd) ApplyPasswd(passwd *passwd.Passwd) {
	passwd.Register("plain", p)
	passwd.SetFallthrough(p)
}

https://github.com/sour-is/go-passwd/blob/main/passwd_test.go#L28-L31

Custom Preference Checks

Circling back to the IsPreferred method. A hasher can define its own IsPreferred method that will be called to check if the current hash meets the complexity requirements. This is good for updating the password hashes to be more secure over time.

func (p *Passwd) IsPreferred(hash []byte) bool {
	_, algo := p.getAlgo(hash)
	if algo != nil && algo == p.d {

		// if the algorithm defines its own check for preference.
		if ck, ok := algo.(interface{ IsPreferred([]byte) bool }); ok {
			return ck.IsPreferred(hash)
		}

		return true
	}
	return false
}

https://github.com/sour-is/go-passwd/blob/main/passwd.go#L62-L74

Example: https://github.com/sour-is/go-passwd/blob/main/pkg/argon2/argon2.go#L104-L133