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