Password pdf recover1/17/2024 ![]() ![]() Subsequent versions of the Adobe PDF format used the RC4 128-bit and the AES 128-bit algorithm for encryption. The major improvement of these encryption algorithms was that the length of the encryption key was increased to 128 bits. Another improvement was the key stretching algorithm, MD5 + RC4 were replaced with 50xMD5 + 20xRC4.Īdobe Acrobat 9 introduced a new format, Adobe PDF 1.7 Extension Level 3, with improved security. The encryption key was increased to 256 bits and the MD5 hash algorithm was replaced with SHA-256. Table 1: Encryption type used by different Adobe PDF versions.Īs can be seen in table 1, early versions of the Adobe PDF format used the RC4 40-bit algorithm for encryption.īy today’s standards, RC4 40-bit encryption algorithm has a short 40-bit key, this weakness allows a direct attack on the encryption key. As a result of this, the RC4 40-bit encryption key of a password protected PDF can be recovered within a day. Although the encryption key collection is finite, a direct key attack is only feasible for PDF files created in Acrobat 2-4 (RC4 40-bit key length). The password recovery tool discussed in this article does not use a direct key attack to access a password protected PDF. Instead, it compares the hashed user and owner password extracted from the PDF with potential passwords supplied by the application user. The algorithm to validate potential passwords depends on the encryption type of the PDF file. Table 1 shows an overview of all the different Adobe PDF formats and their corresponding encryption type. Hence, in order to access a password protected PDF all you have to do is find the encryption key. The maximum number of keys that must be tested in order to find the correct encryption key can be calculated using the formula 2 key length. If an invalid password is entered, the key generated will also be wrong and the file cannot be decrypted. PDF securityīefore discussing the application architecture, I will discuss some PDF security features that are used by this recovery tool. PDF files are decrypted using an encryption key that is generated from the user's password. When the correct password is entered, a program like Adobe Reader calculates the key and uses it to decrypt and display the PDF file. Several print screens of the application are shown below. You can click the pictures to enlarge them.įigure 3: The brute force editor. It uses the itextsharp library to retrieve the hashed user and owner password, after which they are used to validate potential passwords. The application user can supply potential passwords in four different ways, manually by clicking the lock icon, using dictionaries, regular expressions and using a brute force approach. This password recovery tool is a Windows 10 desktop application which provides a way of recovering PDF passwords. The most recent code can be found in my Github repository here, the ClickOnce deployment can be launched here. Furthermore this article should give you insight on how to better protect your PDF documents. The main purpose of this tool is to recover lost PDF passwords. ![]() Before I go further, I want to emphasize that the PDF password recovery tool is not intended to hack anyone's PDF password. ![]() In this article, I will discuss a PDF password recovery tool that I created in WPF using Visual Studio 2015. Unit tests with NUnit parameterized testing.Extract encryption dictionary from PDF using itextsharp.Download EasyPasswordRecoveryPDF.zip - 296.2 KB.
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