Erweiterung von Kurt Jungs gopdf, das leider nicht weiterentwickelt wird https://github.com/jung-kurt/gofpdf
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/*
* 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])
size := len(userPass)
v = make([]byte, size, size)
c.XORKeyStream(v, userPass)
return
}
func (p *protectType) uValueGen() (v []byte) {
var c *rc4.Cipher
c, _ = rc4.NewCipher(p.encryptionKey)
size := len(p.padding)
v = make([]byte, size, size)
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)
}