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Issues with using .NET MD5

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  7 months ago

  by jwood381

  j wood

  nunya, United States

  Joined 7 months ago
  Hello, I am working on implementing some parts of the PDF spec. Currently I am working on getting decryption working Most all of the code I have seen is similiar too pseudocode: Md5 m = new MD5(); m.Init(); m.Update(OwnerPasswordHash); m.Update(Permssions); m.Update(Id[0]); Hash returnHash = m.Finalize(); I have tried doing this with C# in several ways here is the last thing I have tried. MD5 m = new MD5CryptoServiceProvider(); m.Initialize(); int return1 = m.TransformBlock(Padding,0,Padding.Length,Padding,0); byte[] o = Encoding.UTF8.GetBytes(((PdfLiteralString)(encryptionDictionary["O"])).Value); int return2 = m.TransformBlock(o,0, o.Length, o, 0); UInt32 p = (UInt32)((PdfInteger)(encryptionDictionary["P"])).Value; byte[] pBytes = BitConverter.GetBytes(p); int return3 = m.TransformBlock(BitConverter.GetBytes(p),0,BitConverter.GetBytes(p).Length,BitConverter.GetBytes(p),0); byte[] idbytes = Utility.ConvertCharArrayToByteArray(((PdfHexString)id[0]).Value.ToCharArray()); byte[] hash = m.TransformFinalBlock(idbytes, 0, idbytes.Length); but the hash comes back 32 bytes long ... should be 128 and beyond that it may still have other problems as there are still steps remaining to get the key. Any help would be greatly appreciated
  Post was edited on 08/04/2009 23:03:04 Report abuse
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  7 months ago

  by jwood381

  j wood

  nunya, United States

  Joined 7 months ago
  Figured out the key size issue but still having problems with the md5 not being accurate. I would still welcome any pointers from anyone who has implemented this before, but this specific issue is taken care of. J
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  7 months ago

  by jwood381

  j wood

  nunya, United States

  Joined 7 months ago
  Alright could still use some help so heres an update: Ok so here is how the first part of pdf encryption/decryption works in PERL ... (i have verified that this code works); my $md5 = new MD5(); $md5->add($upass); $md5->add($owner_hash); $md5->add($something else...) #after a few more you get my $digest = md5->digest(); so heres the current relevent c# code MD5 m = MD5.Create("MD5"); m.Initialize(); int return1 = m.TransformBlock(Padding,0,Padding.Length,Padding,0); int return2 = m.TransformBlock(o,0, o.Length, o, 0); int return3 = m.TransformBlock(pBytes,0,pBytes.Length,pBytes,0); byte[] hash = m.TransformFinalBlock(idbytes, 0, idbytes.Length); I have check and made sure all the values being used are the same as those in Perl. I even went so far as to do MD5 checksums on each value individually in both perl and c# and they match. Any thoughts ???
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  6 months ago

  by jwood381

  j wood

  nunya, United States

  Joined 7 months ago
  Problem solved. If anyone is interested in seeing the code...just let me know.
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