If you upload an encrypted PDF file, the additional Java files needed for encryption will be added and the user will need a password to open it.To secure a PDF document with password protection and adjusting permissions on the document. Password encryption is now automatically supported in JPedal PDF Library. The main issue is the no-technical one of how to keep the passwords secure. So this makes PDF a secure medium – the file cannot be opened and the data is securely hidden so it is very hard to get it out of the raw file. If you want to decipher something, the longer the example you have, the easier it is. The key is calculated for each PDFObject in the PDF file using local data for each object and the password – that makes it much harder to crack because all the key keeps changing in the data. A key with 128 bits has far more possible values than one with 32 bits, so it is much more secure. They only make sense if altered back using the correct value. All the bytes are changed using the key – unless they are altered back using the same key, they are rubbish and the file cannot be opened. The only way to work it out is to try random combinations – and there are a lot of them…Įncryption is actually done using a key-value (usually 32 or 128 bits in size). But it is much harder to have some data and workout the password from it.
Encryption works in a similar way – given a password, it is easy to encode and decode some data. But it is much harder to do in reverse – given 42 as a value, there is an infinite number of sums. For example, the question ‘what is 6 times 7?’ is easy – it’s 42 (indeed the answer to life, the Universe and Everything according to the writer Douglas Adams).
PDF Encryption relies on the fact that some mathematical functions are much harder to reverse than to do. If you do not have the password, you can still copy the file but not open it. So Acrobat files can be protected with 2 passwords – an Owner password which also allows the user to alter the file and a more limited User password. One of the many reasons people do not put their content online is worries about security – they worry that the material can be repeatedly copied and they will have no control over it. He has an MA in Medieval History and a passion for reading. Mark Stephens Mark has been working with Java and PDF since 1999 and is a big NetBeans fan.
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