From 7623736879a455dc7ecc2772992db61d53698afb Mon Sep 17 00:00:00 2001
From: Kurt Jung <kurt.w.jung@code.google.com>
Date: Tue, 15 Apr 2014 20:22:19 -0400
Subject: [PATCH] Protection file

---
 protect.go | 114 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 protect.go

diff --git a/protect.go b/protect.go
new file mode 100644
index 00000000..e934c2b3
--- /dev/null
+++ b/protect.go
@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2013-2014 Kurt Jung (Gmail: kurt.w.jung)
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+// PDF protection is adapted from the work of Klemen VODOPIVEC for the fpdf
+// product.
+
+package gofpdf
+
+import (
+	"crypto/md5"
+	"crypto/rc4"
+	"encoding/binary"
+	"math/rand"
+)
+
+// Advisory bitflag constants that control document activities
+const (
+	CnProtectPrint      = 4
+	CnProtectModify     = 8
+	CnProtectCopy       = 16
+	CnProtectAnnotForms = 32
+)
+
+type protectType struct {
+	encrypted     bool
+	uValue        []byte
+	oValue        []byte
+	pValue        int
+	padding       []byte
+	encryptionKey []byte
+	objNum        int
+	rc4cipher     *rc4.Cipher
+	rc4n          uint32 // Object number associated with rc4 cipher
+}
+
+func (p *protectType) rc4(n uint32, buf *[]byte) {
+	if p.rc4cipher == nil || p.rc4n != n {
+		p.rc4cipher, _ = rc4.NewCipher(p.objectKey(n))
+		p.rc4n = n
+	}
+	p.rc4cipher.XORKeyStream(*buf, *buf)
+}
+
+func (p *protectType) objectKey(n uint32) []byte {
+	var nbuf, b []byte
+	nbuf = make([]byte, 8, 8)
+	binary.LittleEndian.PutUint32(nbuf, n)
+	b = append(b, p.encryptionKey...)
+	b = append(b, nbuf[0], nbuf[1], nbuf[2], 0, 0)
+	s := md5.Sum(b)
+	return s[0:10]
+}
+
+func oValueGen(userPass, ownerPass []byte) (v []byte) {
+	var c *rc4.Cipher
+	tmp := md5.Sum(ownerPass)
+	c, _ = rc4.NewCipher(tmp[0:5])
+	cap := len(userPass)
+	v = make([]byte, cap, cap)
+	c.XORKeyStream(v, userPass)
+	return
+}
+
+func (p *protectType) uValueGen() (v []byte) {
+	var c *rc4.Cipher
+	c, _ = rc4.NewCipher(p.encryptionKey)
+	cap := len(p.padding)
+	v = make([]byte, cap, cap)
+	c.XORKeyStream(v, p.padding)
+	return
+}
+
+func (p *protectType) setProtection(privFlag byte, userPassStr, ownerPassStr string) {
+	privFlag = 192 | (privFlag & (CnProtectCopy | CnProtectModify | CnProtectPrint | CnProtectAnnotForms))
+	p.padding = []byte{
+		0x28, 0xBF, 0x4E, 0x5E, 0x4E, 0x75, 0x8A, 0x41,
+		0x64, 0x00, 0x4E, 0x56, 0xFF, 0xFA, 0x01, 0x08,
+		0x2E, 0x2E, 0x00, 0xB6, 0xD0, 0x68, 0x3E, 0x80,
+		0x2F, 0x0C, 0xA9, 0xFE, 0x64, 0x53, 0x69, 0x7A,
+	}
+	userPass := []byte(userPassStr)
+	var ownerPass []byte
+	if ownerPassStr == "" {
+		ownerPass = make([]byte, 8, 8)
+		binary.LittleEndian.PutUint64(ownerPass, uint64(rand.Int63()))
+	} else {
+		ownerPass = []byte(ownerPassStr)
+	}
+	userPass = append(userPass, p.padding...)[0:32]
+	ownerPass = append(ownerPass, p.padding...)[0:32]
+	p.encrypted = true
+	p.oValue = oValueGen(userPass, ownerPass)
+	var buf []byte
+	buf = append(buf, userPass...)
+	buf = append(buf, p.oValue...)
+	buf = append(buf, privFlag, 0xff, 0xff, 0xff)
+	sum := md5.Sum(buf)
+	p.encryptionKey = sum[0:5]
+	p.uValue = p.uValueGen()
+	p.pValue = -(int(privFlag^255) + 1)
+}