1/*
2 * Copyright (c) 2013-2014 Kurt Jung (Gmail: kurt.w.jung)
3 *
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
7 *
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 */
16
17// PDF protection is adapted from the work of Klemen VODOPIVEC for the fpdf
18// product.
19
20package gofpdf
21
22import (
23	"crypto/md5"
24	"crypto/rc4"
25	"encoding/binary"
26	"math/rand"
27)
28
29// Advisory bitflag constants that control document activities
30const (
31	CnProtectPrint      = 4
32	CnProtectModify     = 8
33	CnProtectCopy       = 16
34	CnProtectAnnotForms = 32
35)
36
37type protectType struct {
38	encrypted     bool
39	uValue        []byte
40	oValue        []byte
41	pValue        int
42	padding       []byte
43	encryptionKey []byte
44	objNum        int
45	rc4cipher     *rc4.Cipher
46	rc4n          uint32 // Object number associated with rc4 cipher
47}
48
49func (p *protectType) rc4(n uint32, buf *[]byte) {
50	if p.rc4cipher == nil || p.rc4n != n {
51		p.rc4cipher, _ = rc4.NewCipher(p.objectKey(n))
52		p.rc4n = n
53	}
54	p.rc4cipher.XORKeyStream(*buf, *buf)
55}
56
57func (p *protectType) objectKey(n uint32) []byte {
58	var nbuf, b []byte
59	nbuf = make([]byte, 8, 8)
60	binary.LittleEndian.PutUint32(nbuf, n)
61	b = append(b, p.encryptionKey...)
62	b = append(b, nbuf[0], nbuf[1], nbuf[2], 0, 0)
63	s := md5.Sum(b)
64	return s[0:10]
65}
66
67func oValueGen(userPass, ownerPass []byte) (v []byte) {
68	var c *rc4.Cipher
69	tmp := md5.Sum(ownerPass)
70	c, _ = rc4.NewCipher(tmp[0:5])
71	size := len(userPass)
72	v = make([]byte, size, size)
73	c.XORKeyStream(v, userPass)
74	return
75}
76
77func (p *protectType) uValueGen() (v []byte) {
78	var c *rc4.Cipher
79	c, _ = rc4.NewCipher(p.encryptionKey)
80	size := len(p.padding)
81	v = make([]byte, size, size)
82	c.XORKeyStream(v, p.padding)
83	return
84}
85
86func (p *protectType) setProtection(privFlag byte, userPassStr, ownerPassStr string) {
87	privFlag = 192 | (privFlag & (CnProtectCopy | CnProtectModify | CnProtectPrint | CnProtectAnnotForms))
88	p.padding = []byte{
89		0x28, 0xBF, 0x4E, 0x5E, 0x4E, 0x75, 0x8A, 0x41,
90		0x64, 0x00, 0x4E, 0x56, 0xFF, 0xFA, 0x01, 0x08,
91		0x2E, 0x2E, 0x00, 0xB6, 0xD0, 0x68, 0x3E, 0x80,
92		0x2F, 0x0C, 0xA9, 0xFE, 0x64, 0x53, 0x69, 0x7A,
93	}
94	userPass := []byte(userPassStr)
95	var ownerPass []byte
96	if ownerPassStr == "" {
97		ownerPass = make([]byte, 8, 8)
98		binary.LittleEndian.PutUint64(ownerPass, uint64(rand.Int63()))
99	} else {
100		ownerPass = []byte(ownerPassStr)
101	}
102	userPass = append(userPass, p.padding...)[0:32]
103	ownerPass = append(ownerPass, p.padding...)[0:32]
104	p.encrypted = true
105	p.oValue = oValueGen(userPass, ownerPass)
106	var buf []byte
107	buf = append(buf, userPass...)
108	buf = append(buf, p.oValue...)
109	buf = append(buf, privFlag, 0xff, 0xff, 0xff)
110	sum := md5.Sum(buf)
111	p.encryptionKey = sum[0:5]
112	p.uValue = p.uValueGen()
113	p.pValue = -(int(privFlag^255) + 1)
114}
115