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-rw-r--r--protect.go114
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)
+}