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PDF Encyrpt using AES 256

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#6983
Posted: 07/17/2008 16:57:55
by Rob Stephens (Basic support level)
Joined: 07/17/2008
Posts: 1

I am attempting to use the sample TinyEncryptor project to encrypt a PDF file using password encryption using 256 AES encryption. I modified the sample code to add a new choice "AES/256 bits (Acrobat 9)" along with setting "Alg = SBConstants.Unit.SB_ALGORITHM_CNT_AES256;" when that choice is selected. However I receive an exception: "Unsupported algorithm: 28679". I have tried the 40 and 128 bit AES choices and they work fine. I am using SecureBlackBox for .NET version 6.0.0.144 and have version 9 of both Adobe Reader and Acrobat installed on the same system. Is the 256 bit AES encryption not yet supported even though SBConstants.Unit.SB_ALGORITHM_CNT_AES256 is part of the code base?
#6986
Posted: 07/18/2008 00:57:47
by Ken Ivanov (EldoS Corp.)

SecureBlackbox is implemented in the accordance with PDF specification, published by the Adobe Systems, Inc. The latest available revision of the reference (1.7) says nothing about possibilities of encrypting the document with AES256, that's why AES256 support is not available in SBB.

Actually, PDF reference allows using AES256 with a public key (certificate) security handler to encrypt session key information, but *the document* is always encrypted with either RC4 or AES128.

Anyway, we will investigate the details of support for AES256 provided by Acrobat 9. If it uses AES256 to encrypt the session key (as I mentioned above), there will be no problem in publishing a corresponding property, however, I see no actual sense in it, as the document is still encrypted with a weaker cipher.

Quote
Is the 256 bit AES encryption not yet supported even though SBConstants.Unit.SB_ALGORITHM_CNT_AES256 is part of the code base?

SBConstants.Unit.SB_ALGORITHM_CNT_AES256 is a global constant, which can be used with other components of the library.

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