Add optional /Length key in crypt filter dictionary

ChangeLog

@@ -1,5 +1,9 @@
 2013-06-14  Jay Berkenbilt  <ejb@ql.org>
 
+	* Add /Length key to crypt filter dictionary for encrypted files.
+	This key is optional, but some version of MacOS reportedly fail to
+	open encrypted PDF files without this key.
+
 	* Bug fix: properly handle object stream generation when the
 	original file has some compressible objects with generation != 0.
 

libqpdf/QPDFWriter.cc

@@ -726,8 +726,12 @@ QPDFWriter::setEncryptionParametersInternal(
 	std::string method = (this->encrypt_use_aes
                               ? ((V < 5) ? "/AESV2" : "/AESV3")
                               : "/V2");
+        // The PDF spec says the /Length key is optional, but the PDF
+        // previewer on some versions of MacOS won't open encrypted
+        // files without it.
 	encryption_dictionary["/CF"] =
-	    "<< /StdCF << /AuthEvent /DocOpen /CFM " + method + " >> >>";
+	    "<< /StdCF << /AuthEvent /DocOpen /CFM " + method +
+            " /Length " + std::string((V < 5) ? "16" : "32") + " >> >>";
     }
 
     this->encrypted = true;

qpdf/qtest/qpdf/V4-aes-clearmeta.pdf

@@ -327,7 +327,7 @@ endobj
 << /Dest [ 30 0 R /XYZ null null null ] /Parent 73 0 R /Title <0e1c2a38465462707e8c9aa8b6c4d2e04e0071f73ffb55e63fee8c296c57a5116ad91676f573b1c2fe59aca102ad3421cc50bd84f88f518cd8bbd9962c7a59d0> /Type /Outline >>
 endobj
 79 0 obj
-<< /CF << /StdCF << /AuthEvent /DocOpen /CFM /AESV2 >> >> /EncryptMetadata false /Filter /Standard /Length 128 /O <36451bd39d753b7c1d10922c28e6665aa4f3353fb0348b536893e3b1db5c579b> /P -4 /R 4 /StmF /StdCF /StrF /StdCF /U <e4d8eb0d7c43579866926fec0eab59020122456a91bae5134273a6db134c87c4> /V 4 >>
+<< /CF << /StdCF << /AuthEvent /DocOpen /CFM /AESV2 /Length 16 >> >> /EncryptMetadata false /Filter /Standard /Length 128 /O <36451bd39d753b7c1d10922c28e6665aa4f3353fb0348b536893e3b1db5c579b> /P -4 /R 4 /StmF /StdCF /StrF /StdCF /U <e4d8eb0d7c43579866926fec0eab59020122456a91bae5134273a6db134c87c4> /V 4 >>
 endobj
 xref
 0 80
@@ -413,5 +413,5 @@ xref
 0000014817 00000 n 
 trailer << /Info 2 0 R /Root 1 0 R /Size 80 /ID [<66d36a30a97e0f16f39955c6221e0c2a><31415926535897932384626433832795>] /Encrypt 79 0 R >>
 startxref
-15129
+15140
 %%EOF

qpdf/qtest/qpdf/V4-aes.pdf

@@ -306,7 +306,7 @@ endobj
 << /Dest [ 30 0 R /XYZ null null null ] /Parent 73 0 R /Title <0e1c2a38465462707e8c9aa8b6c4d2e0a57e63f459f8a8428dfc859f799038f972379574e01ef823841a76dbefaa14665223960437217436968f6261cc32feb9> /Type /Outline >>
 endobj
 79 0 obj
-<< /CF << /StdCF << /AuthEvent /DocOpen /CFM /AESV2 >> >> /Filter /Standard /Length 128 /O <36451bd39d753b7c1d10922c28e6665aa4f3353fb0348b536893e3b1db5c579b> /P -4 /R 4 /StmF /StdCF /StrF /StdCF /U <32c27288b9ec6a4fab94e6188828595c0122456a91bae5134273a6db134c87c4> /V 4 >>
+<< /CF << /StdCF << /AuthEvent /DocOpen /CFM /AESV2 /Length 16 >> >> /Filter /Standard /Length 128 /O <36451bd39d753b7c1d10922c28e6665aa4f3353fb0348b536893e3b1db5c579b> /P -4 /R 4 /StmF /StdCF /StrF /StdCF /U <32c27288b9ec6a4fab94e6188828595c0122456a91bae5134273a6db134c87c4> /V 4 >>
 endobj
 xref
 0 80
@@ -392,5 +392,5 @@ xref
 0000014404 00000 n 
 trailer << /Info 2 0 R /Root 1 0 R /Size 80 /ID [<66d36a30a97e0f16f39955c6221e0c2a><31415926535897932384626433832795>] /Encrypt 79 0 R >>
 startxref
-14693
+14704
 %%EOF