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| -rw-r--r-- | protect.go | 114 |
1 files changed, 114 insertions, 0 deletions
diff --git a/protect.go b/protect.go new file mode 100644 index 0000000..e934c2b --- /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) +} |