From b7dcbc22deb5f04edd0fd47e9b2b0b9ffdb89101 Mon Sep 17 00:00:00 2001
From: Denys Smirnov <denys@sourced.tech>
Date: Wed, 19 Sep 2018 23:48:50 +0300
Subject: [PATCH] core: fix standard crypt filter name; resolves issues with
 Adobe Reader

---
 pdf/core/crypt.go      | 14 +++++++++-----
 pdf/core/crypt_test.go |  2 +-
 pdf/model/writer.go    |  2 +-
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/pdf/core/crypt.go b/pdf/core/crypt.go
index 211e3395..a1466d4b 100644
--- a/pdf/core/crypt.go
+++ b/pdf/core/crypt.go
@@ -77,6 +77,9 @@ const padding = "\x28\xBF\x4E\x5E\x4E\x75\x8A\x41\x64\x00\x4E\x56\xFF" +
 	"\xFA\x01\x08\x2E\x2E\x00\xB6\xD0\x68\x3E\x80\x2F\x0C" +
 	"\xA9\xFE\x64\x53\x69\x7A"
 
+// StandardCryptFilter is a default name for a standard crypt filter.
+const StandardCryptFilter = "StdCF"
+
 // CryptFilter represents information from a CryptFilter dictionary.
 // TODO (v3): Unexport.
 type CryptFilter struct {
@@ -230,6 +233,7 @@ func (crypt *PdfCrypt) SaveCryptFilters(ed *PdfObjectDictionary) error {
 		cf.Set(PdfObjectName(name), v)
 
 		v.Set("Type", MakeName("CryptFilter"))
+		v.Set("AuthEvent", MakeName("DocOpen"))
 		v.Set("CFM", MakeName(string(filter.Cfm)))
 		v.Set("Length", MakeInteger(int64(filter.Length)))
 	}
@@ -280,7 +284,7 @@ func PdfCryptMakeNew(parser *PdfParser, ed, trailer *PdfObjectDictionary) (PdfCr
 			crypter.V = int(*V)
 			// Default algorithm is V2.
 			crypter.CryptFilters = CryptFilters{}
-			crypter.CryptFilters["Default"] = CryptFilter{Cfm: "V2", Length: crypter.Length}
+			crypter.CryptFilters[StandardCryptFilter] = CryptFilter{Cfm: "V2", Length: crypter.Length}
 		} else if *V >= 4 && *V <= 5 {
 			crypter.V = int(*V)
 			if err := crypter.LoadCryptFilters(ed); err != nil {
@@ -766,7 +770,7 @@ func (crypt *PdfCrypt) Decrypt(obj PdfObject, parentObjNum, parentGenNum int64)
 
 		dict := so.PdfObjectDictionary
 
-		streamFilter := "Default" // Default RC4.
+		streamFilter := StandardCryptFilter // Default RC4.
 		if crypt.V >= 4 {
 			streamFilter = crypt.StreamFilter
 			common.Log.Trace("this.StreamFilter = %s", crypt.StreamFilter)
@@ -821,7 +825,7 @@ func (crypt *PdfCrypt) Decrypt(obj PdfObject, parentObjNum, parentGenNum int64)
 	if s, isString := obj.(*PdfObjectString); isString {
 		common.Log.Trace("Decrypting string!")
 
-		stringFilter := "Default"
+		stringFilter := StandardCryptFilter
 		if crypt.V >= 4 {
 			// Currently only support Identity / RC4.
 			common.Log.Trace("with %s filter", crypt.StringFilter)
@@ -1016,7 +1020,7 @@ func (crypt *PdfCrypt) Encrypt(obj PdfObject, parentObjNum, parentGenNum int64)
 
 		dict := so.PdfObjectDictionary
 
-		streamFilter := "Default" // Default RC4.
+		streamFilter := StandardCryptFilter // Default RC4.
 		if crypt.V >= 4 {
 			// For now.  Need to change when we add support for more than
 			// Identity / RC4.
@@ -1073,7 +1077,7 @@ func (crypt *PdfCrypt) Encrypt(obj PdfObject, parentObjNum, parentGenNum int64)
 	if s, isString := obj.(*PdfObjectString); isString {
 		common.Log.Trace("Encrypting string!")
 
-		stringFilter := "Default"
+		stringFilter := StandardCryptFilter
 		if crypt.V >= 4 {
 			common.Log.Trace("with %s filter", crypt.StringFilter)
 			if crypt.StringFilter == "Identity" {
diff --git a/pdf/core/crypt_test.go b/pdf/core/crypt_test.go
index 0852354f..ca9b4af3 100644
--- a/pdf/core/crypt_test.go
+++ b/pdf/core/crypt_test.go
@@ -149,7 +149,7 @@ func TestDecryption1(t *testing.T) {
 	crypter.DecryptedObjects = map[PdfObject]bool{}
 	// Default algorithm is V2 (RC4).
 	crypter.CryptFilters = CryptFilters{}
-	crypter.CryptFilters["Default"] = CryptFilter{Cfm: "V2", Length: crypter.Length}
+	crypter.CryptFilters[StandardCryptFilter] = CryptFilter{Cfm: "V2", Length: crypter.Length}
 	crypter.V = 2
 	crypter.R = 3
 	crypter.P = -3904
diff --git a/pdf/model/writer.go b/pdf/model/writer.go
index 83ff8698..edc0cc4c 100644
--- a/pdf/model/writer.go
+++ b/pdf/model/writer.go
@@ -527,7 +527,7 @@ func (this *PdfWriter) Encrypt(userPass, ownerPass []byte, options *EncryptOptio
 		return fmt.Errorf("unsupported algorithm: %v", options.Algorithm)
 	}
 	const (
-		defaultFilter = "Default"
+		defaultFilter = StandardCryptFilter
 	)
 	crypter.CryptFilters[defaultFilter] = cf
 	if crypter.V >= 4 {