unipdf/core/security/handlers.go

/*
 * This file is subject to the terms and conditions defined in
 * file 'LICENSE.md', which is part of this source code package.
 */

package security

import "fmt"

// StdHandler is an interface for standard security handlers.
type StdHandler interface {
	// GenerateParams uses owner and user passwords to set encryption parameters and generate an encryption key.
	// It assumes that R, P and EncryptMetadata are already set.
	GenerateParams(d *StdEncryptDict, ownerPass, userPass []byte) ([]byte, error)

	// Authenticate uses encryption dictionary parameters and the password to calculate
	// the document encryption key. It also returns permissions that should be granted to a user.
	// In case of failed authentication, it returns empty key and zero permissions with no error.
	Authenticate(d *StdEncryptDict, pass []byte) ([]byte, Permissions, error)
}

// StdEncryptDict is a set of additional fields used in standard encryption dictionary.
type StdEncryptDict struct {
	R int // (Required) A number specifying which revision of the standard security handler shall be used.

	P               Permissions
	EncryptMetadata bool // Indicates whether the document-level metadata stream shall be encrypted.

	// set by security handlers:

	O, U   []byte
	OE, UE []byte // R=6
	Perms  []byte // An encrypted copy of P (16 bytes). Used to verify permissions. R=6
}

// checkAtLeast checks the size of the bytes field and returns a descriptive error if it doesn't.
func checkAtLeast(fnc, field string, exp int, b []byte) error {
	if len(b) < exp {
		return errInvalidField{Func: fnc, Field: field, Exp: exp, Got: len(b)}
	}
	return nil
}

type errInvalidField struct {
	Func  string
	Field string
	Exp   int
	Got   int
}

func (e errInvalidField) Error() string {
	return fmt.Sprintf("%s: expected %s field to be %d bytes, got %d", e.Func, e.Field, e.Exp, e.Got)
}