Function Compare

coderd/userpassword/userpassword.go:75–110

Compare checks the equality of passwords from a hashed pbkdf2 string. This uses pbkdf2 to ensure FIPS 140-2 compliance. See: https://csrc.nist.gov/csrc/media/templates/cryptographic-module-validation-program/documents/security-policies/140sp2261.pdf

(hashed string, password string)

// uses pbkdf2 to ensure FIPS 140-2 compliance. See:
// https://csrc.nist.gov/csrc/media/templates/cryptographic-module-validation-program/documents/security-policies/140sp2261.pdf
func Compare(hashed string, password string) (bool, error) {
	// If the hashed password provided is empty, simulate comparing a real hash
	// to preserve timing. The simulated hash is derived from a random value, so
	// the comparison below can never succeed.
	if hashed == "" {
		hashed = simulatedHash.Load()
	}

	if len(hashed) < hashLength {
		return false, xerrors.Errorf("hash too short: %d", len(hashed))
	}
	parts := strings.SplitN(hashed, "$", 5)
	if len(parts) != 5 {
		return false, xerrors.Errorf("hash has too many parts: %d", len(parts))
	}
	if len(parts[0]) != 0 {
		return false, xerrors.Errorf("hash prefix is invalid")
	}
	if parts[1] != hashScheme {
		return false, xerrors.Errorf("hash isn't %q scheme: %q", hashScheme, parts[1])
	}
	iter, err := strconv.Atoi(parts[2])
	if err != nil {
		return false, xerrors.Errorf("parse iter from hash: %w", err)
	}
	salt, err := base64Encoding.DecodeString(parts[3])
	if err != nil {
		return false, xerrors.Errorf("decode salt: %w", err)
	}

	if subtle.ConstantTimeCompare([]byte(hashWithSaltAndIter(password, salt, iter)), []byte(hashed)) != 1 {
		return false, nil
	}

	return true, nil
}

// Hash generates a hash using pbkdf2.
// See the Compare() comment for rationale.