Decompiling Java 221
| Decompiling Java | |
| author | Godfrey Nolan |
| pages | 264 |
| publisher | apress |
| rating | 8/10 |
| reviewer | Richard Rodger |
| ISBN | 1590592654 |
| summary | Learn how decompilation works in order to properly protect your intellectual property. |
If you are interested in Decompiling Java, then this book tell you exactly how to do that. There's no fluff and every chapter counts. I can safely concur that Fiachra's observations are indeed correct. You'd better be prepared for some serious hard core details, but then that's what you'd paid for. It is really great to read a book that doesn't end each chapter with a few links to the real material because the author couldn't be bothered to write it up.
So what do you get? As a battle-hardened Java coder of not a few years programming, I wanted to find out about the gory details of bytecodes and how to get at them. Now it's a subject I always knew I should know about, but never took the time to read up on it. Decompiling Java puts all that knowledge into one place.
Here's a quick run-through of the chapters so you know what you're getting:
Ch.1 IntroductionDecompilation isn't just another coding tool - there are other, real world issues like ending up in jail to think about. Godfrey proposes a sort of code-of-honour for decompilers. This book could so easily have been positioned for the fr33ky kod3r skript kiddie market, and I'm glad that the author and publishers took a mature and sensible approach to the subject. I have had to decompile purchased code because of bugs and I'm glad that someone took the time to think about an ethical framework for doing this.
Ch.2 Ghost in the Machine
A good and solid introduction to the JVM and the classfile format. If you're in the market for this book, you probably already know most of this, but a refresher course is always good. For me, it definitely sorted out a lot on internal hand-waving on the subject. Just remember kids, the only thing to fear is fear itself - it's only binary data after all.
Ch.3 Tools of the Trade
Although the author builds his only decompiler later in the book, it nice to get a chapter devoted to the existing toolset and the Java decompiler scene.
Ch. 4 Protecting your Source
For the honest developer, knowing how to decompile code is more about protecting your own source code than breaking someone else's (who wants to read other people's smelly code anyway!). This chapter is one of the most directly practical. I had always assumed that obfuscation was a magic fix that I could apply if necessary. In reality, good obfuscation is just like good encryption (that is, uncommon, difficult to verify, and still subject to lateral attacks). Even compiled bytecode has relatively low entropy, so the value of obfuscation must be considered carefully.
Ch.5 Decompiler Design
This is were it starts getting a wee bit technical. Decompilation, as you can imagine, is a bit of a black art, and there are many ways of doing it. Some of them involve scary maths and some involve scary coding and the rest both. But that's why you don't meet many people who can write decompilers. Godfrey does a great job of taking you on a practical run through this fog of decompilers. At the end of this chapter you will be able to decide for yourself what approach is best suited to your problem domain. Again, this material can be challenging but it's like boot camp: You just gotta.
Ch.6 Decompiler Implementation
If the previous chapter hurt your brain and scared you silly then this chapter will have you weeping for joy. The author takes a practical, effective, and most importantly, understandable approach to actually implementing a compiler. Now, as he freely admits, his design may encounter difficulties with edge effects and infrequently used idioms, but it will take you to the point where you can solve them yourself. I really had to smile at how simple and effective the approach taken here is - instead of the expected multiple passes and mind bending parse tree manipulation, we have a single-pass, source-generating decompiler for Java. You won't follow it all first time, but it does work and you can verify it for yourself. Like I said at the start, you don't get that empty feeling from this book, and this chapter is pretty much why. I bought a book about decompiling Java, and now I can.
Ch.7 Case Studies
This chapter addresses the "why" of decompiling, returning again to the moral questions raised at the start. It's more food for thought than prescriptive preaching though, which again is refreshing. I have admit to dipping into this chapter while reading the rest of the book - the human interest angle always works a treat!
Of course, no book is perfect. What I think could have helped a bit overall would have been a introductory chapter to bytecode. But it's not a great loss and bytecode is actually pretty simple once you get your head around it. Still it might have lessened the learning curve somewhat.
Decompiling Java is a great addition to that section of your bookshelf dedicated to serious books that will be around for a while. The JVM specification and Java bytecode are not going to change that much, so this book is something you'll be able to use for a long time. Personally the best thing about this book for me was that it took me to the next level. Not many books can do this. As a working coder, I pretty much put things like decompilation into the "too hard, just for academics, and I could never grok it", category. It's great when a book comes along that can can you out of that comfort zone.
You can purchase Decompiling Java from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, carefully read the book review guidelines, then visit the submission page.
no bytecode intro? (Score:4, Interesting)
Re:no bytecode intro? (Score:5, Funny)
Re:no bytecode intro? (Score:2)
A good and solid introduction to the JVM and the classfile format. If you're in the market for this book, you probably already know most of this, but a refresher course is always good. For me, it definitely sorted out a lot on internal hand-waving on the subject. Just remember kids, the only thing to fear is fear itself - it's only binary data after all.**
maybe that one has the bytecode covered in short?
btw.. for everyone thinking that obfuscators do a good job.. THEY DON'T! es
Re:no bytecode intro? (Score:2)
obfuscators don't work? (Score:3, Insightful)
I'm not talking about tiny programs; but who even bothers decompiling tiny midlets? Isn't it obvious what they're doing? With tiny programs, if you know enough to be cracking Java programs, you might as well just write the thing out yourself. It's not magic.
But for larger applications, any decent obfuscator can make it very time-consuming to decompile and edit the programs.
Re:no bytecode intro? (Score:4, Informative)
Better Java Book (Score:4, Informative)
Re:Better Java Book (Score:4, Informative)
Decompiling Java:
Writing for those who want to learn Java by decompilation, Nolan, a specialist in web site optimization, explains how to turn partially compiled Java bytecodes back into source code so that readers can see what the original programmer was thinking. Early chapters unravel the Java classfile format and show how Java code is stored as bytecode and executed by the JVM. Later chapters focus on how to write a Java decompiler, and a final chapter offers case studies.
Both Java and
For example, how secure is your code after you run an obfuscator? The book will answer questions like this, and provide more thorough information about Java byte codes and the Java Virtual Machine (JVM) than any other book on the market. This book redresses the imbalance by providing insights into the features and limitations of today's decompilers and obfuscators, and offering a detailed look at what JVM's actually do.
This is a fantastic in-depth book on decompilers and code obfuscation tools for Java. It covers the structure of Java code files, the opcodes, and the all of the tools required to decompile classes, and to obfuscate existing code. It's an invaluable reference for anyone who has to deploy Java in a non-secure environment, or for those that want to learn how the language really works.
There is a lot of code to pour though, and there are no illustrations. I think the text could have used some illustrations, but that's not a big sticking point for me.
If you are a serious Java gearhead you should have a look at this book. And if you have a specific interest in either de-compiling some Java or obscuring your deployed Java bytecode then this is a must have.
Covert Java:
"Covert Java" provides a fascinating and look at behind the scenes Java development tactics that are usually the domain of seasoned veterans. Definitely a read for those who want to master Java.
--Floyd Marinescu, Author, EJB Design Patterns; General Manager & founder of TheServerSide Communities.
As a Java developer, you may find yourself in a situation where you have to maintain someone else's code or use a third-party's library for your own application without documentation of the original source code. Rather than spend hours feeling like you want to bang your head against the wall, turn to Covert Java: Techniques for Decompiling, Patching, and Reverse Engineering. These techniques will show you how to better understand and work with third-party applications. Each chapter focuses on a technique to solve a specific problem, such as obfuscation in code or scalability vulnerabilities, outlining the issue and demonstrating possible solutions. Summaries at the end of each chapter will help you double check that you understood the crucial points of each lesson. You will also be able to download all code examples and sample applications for future reference from the publisher's website. Let Covert Java help you crack open mysterious codes!
Been decompiling Java for awhile now... (Score:5, Funny)
Better watch it... (Score:2)
another alternative = encrypted class files (Score:5, Interesting)
the details of the paper are:
1999 - Security in Set-Top boxes
European Multimedia, Embedded Systems and Electronic Commerce
EMMSEC '99, Stockholm, SWEDEN
June 21-23, 1999
COPY: (pdf)
http://www.ardiri.com/publications/emmsec9
there was a lot of interest on this topic back in the time
Re:another alternative = encrypted class files (Score:4, Informative)
Doesn't work (Score:5, Informative)
There are a number of papers and articles detailing why this type of approach to "IP security" is so misguided. One such article is here: http://www.javaworld.com/javaworld/javaqa/2003-05
The crux is that at some point in time, you have to deliver the encrypted class to the JVM in an unencrypted format. Intercepting this delivery is incredibly easy (no expert knowledge required, the details for doing so are detailed in the article above), at which time someone can just write the unecrypted class file out to disk (or wherever they wish). Voila! All your IP are belong to us.
Re:Doesn't work (Score:4, Informative)
Are you confusing encryption with obfuscation? If not I agree that class-level encryption has no ROI.
Obfuscation, on the other hand, is an excellent tool for protecting IP. I use Proguard http://proguard.sourceforge.net/ [sourceforge.net] via Ant and am happy with the result, having tried to grok the resulting byte code (using jad...) Good luck trying to work with that!
R7
Obfuscation issues (Score:2)
Though obfuscation comes with its own array of potential issues, especially in remote applications or those that rely on reflection
Obfuscators pretty much all offer you enough flexibility to exclude classes that will need to be used via reflection or with RMI... or to
Re:Doesn't work (Score:2)
until JVM architecture changes to, say, support class decoding inside native code...
This is already possible and I have implemented it. It involves making direct calls to the jvm libraries from JNI rather than callbacks to java from JNI. There is still a way to get the bytes, but it invo
What ethical problems? (Score:5, Insightful)
What ethical problems? Decompiling is perfectly moral and ethical. Whether it is illegal is a seperate and, for me, almost irelevant issue. If I legally own a copyrighted work I am allowed to read it, period and end of story. Corporate licences excepted, software is SOLD, not licensed despite the scary words on the box and the dread click through EULA.
Hell, I learned assembly by writing a disassembler (in BASIC) and reading the Microsoft BASIC roms, then later reading the commented listings that ran in Color Computer Magazine. (TO avoid a copyright fight, and because M$ refused to grant them permission, CCM ran only the comments and memory locations, leaving the reader to run their own dissassembly for the opcodes.)
The only ethical problem would be lifting the code and reusing it without permission and I think we all know that is wrong.
Re:What ethical problems? (Score:3, Insightful)
I disagree here. I am a strong believer that people should be able to trade goods/services for prices/conditions they mutually agree upon. If I write software and say I will sell it to you for $x on condition that you do Y
Re:What ethical problems? (Score:5, Interesting)
While you are welcome to your delusions, but out here in the real world we have some things called laws. Specifically the Uniform Commercial Code and the Copyright laws.
You will note that I excepted commercial licenses, since those are actual signed contracts and are legally binding.
According to the Uniform Commercial Code if goods are exchanged in regular trade there can't be strings attached; i.e. if it looks like a sale it IS a sale. If I buy a copy of Microsoft Windows from Newegg.com I did just that, I BOUGHT a copy of Windows. That means I can do anything with that copy, including read it. I can even copy it in whole or in part so long as such activity falls under the backup exception written into the law or by Fair Use. Of course any other reproduction is forbidden by the artifical monopoly rights granted to the author by copyright. While I have a lot of problems with how copyrights are currently operated (eternal instead of "limited times" as prescribed by the Constituition) I don't have a major problem with that limitation.
But think about it, what you are saying is that you can sell me a copyrighted work that I am forbidden to read myself. What a load of fetid dingos kidneys! Ford can't forbid me from taking apart a Caddy and not only making, but SELLING plans; but you think your algorithms are so freaking special that you want the government to put me in jail for the crime of reading them? What are you smoking?
Re:What ethical problems? (Score:2, Interesting)
Sure. I was thinking of this as an example when I wrote my last post. I could write a book, and say to you, "Here's my book, it's $5, but if you buy it you can't read chapters 3, 7, or 9." And I'd have no problem with that. If you don't want to pay money for a book whose full contents I say you can't read, then fine - don't buy it. But don't buy it, knowing what terms I've laid out, and
Re:What ethical problems? (Score:2)
You can certainly restrict your customers such terms -- as long as you convince the buyer to read and sign a legally binding contract prior to the sale.
If you don't get a signature, you can't expect any restrictions.
Re:What ethical problems? (Score:2)
Why do you think I am for hiding or "tricking" people? I said in my original post, in very clear terms, that conditions are only valid if the buyer understands and agrees to them.
Re:What ethical problems? (Score:3, Insightful)
Very.
I just don't understand people with your greedy, assbackwards, mindset.
I don't understand people with your mindset, a mindset that strips individuals of their rights. Listen, if I have created something, and want to sell it to you with conditions, why shouldn't I be able to do that? If you don't want to abide by those conditions: DON'T FREAKING BUY WHAT I'M SELLING. Have a little restraint, Mr. Consumer. Jebus.
I am 100% for free trade between people. You, on the othe
Re:What ethical problems? (Score:2)
Wow. Your talking about copyright law, which is an artificial monopoly. Your 100% free trade would work just fine if copyright did not create an artificial monopoly which is why there are laws spelling out what can and can't be done with copyrighted works If people enter in
Re:What ethical problems? (Score:3, Interesting)
Re:What ethical problems? (Score:2, Funny)
Re:What ethical problems? (Score:2)
So if I write some material and I state that part of our agreement is that you cannot read certain sections of it - by purchasing it you are agreeing to my terms and can be held liable in a civil court. Remember - in term
Re:What ethical problems? (Score:2)
Re:What ethical problems? (Score:2)
First you imply that the actual laws are irrelevant to your views on morality:
Then when someone argues on moral grounds:
Re:What ethical problems? (Score:2)
> morality:
When a society is correctly operating, laws codify morals. In our current dystopia of the Law divorced from Truth and Justice that isn't always the case. It is the Right, nay it is the Duty, of every citizen in a free society to violate an unjust law as an act of civil disobiedience.
And yes, I have done so publicly, specifically by confessing to violating the DMCA by viewing DVDs on my laptop in a letter to President
Re:What ethical problems? (Score:2)
You're talking about specific laws here. The grandparent post was merely saying that violating an a
Re:What ethical problems? (Score:2)
> immoral.
True enough but this whole matter revolves around whether an agreement exists. When people disagree on such matters, that is where the Law comes into the discussion and it is very clear on the point.
The original poster holds that as the creator and owner of a work he has absolute power to dictate the terms and conditions it can be USED under, and that by purchasing his work I MUST agree to those terms. I hold that he
Re:What ethical problems? (Score:2)
> buying Windows XP, you're buying a LICENSE to use Windows XP in binary
> form. Huge difference.
Still hung up on that misconception. No, a license is only in effect if I sign a contract changing the sale into a limited license. They can print "By buying this hammer you agree you will ONLY drive our brand of nails and strike no other object with this tool." on the side, stock the shelves of Home Depot with them and get exact
Re:What ethical problems? (Score:2)
> you a LICENSE to use their products.
Nope. on the rare occasion I buy software, I BUY it. You do not need a license to use software anymore than you need one to read a book, or even to check one out of a public library.
> Then the GPL, the MPL, and every other open source license, is invalid.
> That makes WhiteBox Linux illegal.
Again, you are quite mistaken. You may download as many copies of WhiteBox from whereever you p
Re:What ethical problems? (Score:2)
Er, because if you distribute it, you're distributing someone else's copyrighted works. *DISTRIBUTING*. Not copying/modifying/studying for your own private use, *DISTRIBUTING*. The only way you could do that is with the copyright holder's permission, which happens to be spelled out in the GPL. That's how copyright law works, and that's the whole
Re:What ethical problems? (Score:3, Insightful)
> anything to use GPL'd software, or copy it, or distribute it, as long
> as they meet its conditions. So if I don't have to sign anything, then
> the GPL isn't binding.
Exactly correct. If you copy a GNU program and distribute it you do not have to accept the GPL. However when RMS and his squadron of elite attack lawyer ninjas descend upon you for violating their copyright, smiting thee with their rightous fury, only saying "I
Re:What ethical problems? (Score:2)
If it's a unidirectional causality, then a moral assessment should never depend on any particular laws. The original poster claimed that unapproved decompilation was immoral. Then jmorris42 came around and started citing specific laws to prove that he had the legal right to do so.
What's wors
Re:What ethical problems? (Score:2)
> and proceeded to draw further conclusions from that assumption
No, read up the thread, in the very first post I excluded the case of corporate site licensing and other such real signed contract sort of software licensing it should be clear I am discussing consumer EULAs.
I assert that since EULAs are wrong on both moral and legal grounds, either of which alone is cause for ignoring them. I claim that I have as much right to r
Re:What ethical problems? (Score:2)
Especially seeing how Cadillac is a GM brand.
Re:What ethical problems? (Score:5, Insightful)
Re:What ethical problems? (Score:2)
I agree with you fully. Burying what you can and can't do in a EULA, one that you can't read until you take the software home and start installing it, is not what I have in mind. If they wanted to impose such conditions on the software's use, it would behoove them to have on
Re:What ethical problems? (Score:2)
Re:What ethical problems? (Score:2)
Re:What ethical problems? (Score:3, Insightful)
Re:What ethical problems? (Score:2)
Re:What ethical problems? (Score:2)
Regardless of the ethics... (Score:2)
Regardless of the ethics, reading other people's code is, IMHO, the single best way to learn how coding works. And decompiling from objec
This is one of the features of Java (Score:2, Insightful)
As systems get more open/advanced, the sources are more difficult to hide. In case of web apps, there is no need to decompile anything, the javascripts are
Re:This is one of the features of Java (Score:2)
I'm not sure why you think of NTFS file streams. That's a complete different issue. How would your trick work if the ASP pages are on a FAT file system? NTFS streams are interesting: I once used them in a pratical joke to consume all of somebody's disk space. They couldn't see in Explorer where it went! Incidentally, it's too bad that Macs can't make use of them for their resource forks when browsing
Re:This is one of the features of Java (Score:2)
Re:This is one of the features of Java (Score:2, Interesting)
Why? Well, Java bytecode is a lot more flexible than the Java language. Take exceptions for example. In the language we handle exceptions with try-catch-finally grammar productions. But in the bytecode we have a table that specifes ranges of bytecode addresses that mapped via an exception to a exception handler. The cute thing is that a "range of bytecodes" has nothing t
Re:This is one of the features of Java (Score:3, Insightful)
Web applications are typically implemented server-side. Javascript is client-side code.
Javascript != web applications
Perhaps what you are referring to is the source for ASP and JSP/servlets. There have been bugs in servlet containers (specifically, I bel
Re:This is one of the features of Java (Score:4, Insightful)
Even more advanced applications that use ASP pages that execute on the server, can be seen by changing the URL to list the source rather than execute them
Are you smoking crack?
You can't arbitrarily get at source code on someone's web server. Do you think eBay would want you seeing the passwords to their database servers?
Web apps aren't written in JavaScript. Sure, there might be some to drive calendar selection or something, but pretty much all real apps (shopping carts, etc.) are done server side.
Please get a clue and stop spreading your FUD around.
Additionally, this isn't a "feature" of Java. It's just a side-effect of its machine-independent bytecode. You could argue that it's not all that hard to reverse engineer compiled C - if you step it through a debugger you can see what it does fairly easily.
Systems being more "advanced" (let's wave our hands a little bit more) won't make it any more difficult to hide the source. Many many people run Java on the server side of web apps. It will always be impossible to view the source for such applications (unless the developers put it up for the world to see, of course). As for being "open", what do you mean? If you mean, "open source" then, well, duh...
Re:This is one of the features of Java (Score:2, Informative)
I think he's referring to an old bug on IIS that would allow you to view the contents of a file on the server. I believe it was a sample ASP that MS included to demonstrate come capability of ASPs.
I'm sure there are a few servers around that still have that enabled, but I'm sure most had that thing fixed 3-4 years ago.
DJ Decompiler and JAD (Score:3, Informative)
Oh, and obfuscation, blah, any good IDE (like IntelliJ IDEA) is able to help you work around this junk.
Being able to decompile code.... (Score:5, Interesting)
Anyhow, decompiling the classfile with "javap -c" shows that a couple of instructions get eliminated by dropping the explicit comparison to "true". So the classfile gets smaller, it loads faster, and (unless the JIT compiler is smart enough to do constant propagation on that conditional) it'll run faster, too.
Which is really surprising to me (Score:4, Insightful)
who, as a compiler hacker, would have expected an optimization pass to transform the first form into the second form before generating the bytecode.
Or more precisely, to understand that both forms are testing for the same thing, and to produce identical simplified bytecode.
Re:Which is really surprising to me (Score:2)
Yeah. Another result - this code results in the "if" statement body being optimized away:
but this doesn't:
But who knows - the JIT compiler may discard those bytecodes at runtime. Hard to say...
Re:Which is really surprising to me (Score:2)
Re:Which is really surprising to me (Score:2)
Almost all of the Java compilers out there do little to no optimizations while generating bytecode. Rather, the focus of the compilers is to generate bytecode that is easily understood and optimized by the virtual machine.
Since the bytecode for Java is a well-defined standard, there are many more bytecode processors for Java compared to say object-code proc
Re:Which is really surprising to me (Score:2)
On the other hand, also speaking as a compiler hacker, I should point out that just because an optimisation is possible, doesn't mean it's a good idea. When you add more optimisation, it costs. It's extra code that you have to write, test and maintain over the life of the compiler. If its entire purpose is to make the rare case of badly written code go faster, then you could quite legitimately turn around to the compiler user and say "don't do that".
As an example, a compiler could quite easily optimise
Re:Being able to decompile code.... (Score:4, Informative)
mov eax, isLoggable
cmp eax, 0
jnz skip_if
skip_if:
A check to true only changes the cmp to 1 instead of 0. It won't run any faster.
Re:Being able to decompile code.... (Score:2)
> machine level.
Yup, for assembler, that makes sense. But for Java bytecode, the explicit comparison is resulting in this:vsSo there's a least one extra instruction in there. Of course, again, what the JIT compiler might do with this is something else entirely.
Re:Being able to decompile code.... (Score:2)
The Java Language spec requires that a conforming compiler (not JIT, but source to bytecode compiler) do constant propagation.
Re:Being able to decompile code.... (Score:2)
Hm. I knew that the JLS required that in some circumstances - i.e., so that a switch statement can switch on a static final. What's the actual requirement, though? For example:Is a conforming compiler also required to make that transformation?
Re:Being able to decompile code.... (Score:2)
Re:Being able to decompile code.... (Score:3, Informative)
The Java compiler does some optimization - for example, when given this code:
it does algebraic simplification to reduce that assignment to an aload followed by a iconst_4 instruction. And it does some constant propagation so that this:
also gets simplified to the aload/const sequence. I guess it's just some choices the compile designers made on which things wer
You didn't sell it. (Score:5, Insightful)
>knowing how to decompile code is more about protecting your own source code.
There are many reasons to learn about, implement and use decompilers, but I don't think "to properly protect your intellectual property" should be one of them.
I'm got somewhat interested in this book (never heard about it before), but I think I'm going to pass. Sounds like the decompiling described is too much of a one-trick pony -- which is fine, it's about decompiling java after all -- but I'd really like something like an extension and update of Cifuentes work in book form, with the lessons from the IDA team too.
You know, from the beginning; starting with machine descriptions and disassembly for a generic front-end, efficent IR, and on up through the back end.
Now that'd be a tome [worth paying for].
In Soviet Russia... (Score:3, Funny)
Er... um...
the compiler decompiles you!
Er...
the java decompiles itself!
Ah, whatever.
- Kevin
You're getting it wrong (Score:2)
Maintainance nightmare (Score:2, Insightful)
Let me get this straight: the author recommends that 'honest' developers obfuscate their code?
I've read programs that I thought were obfuscated, but later found out were just poorly written. Other times I've run into programmers who, tin hats firmly affixed, went to great lengths to make sure no one learned their Merlinesque techniques for getting the most out of BASIC.
In context, the author seems to be talkin
Re:Maintainance nightmare (Score:5, Insightful)
Re:Maintainance nightmare (Score:5, Informative)
Re:Maintainance nightmare (Score:2)
>byte code, not source code
>feature of the language...
My comments were intended to be more general than the Java language. Whether done with a command line switch, on an IDE checkbox at packaging time, or by writing a quickie program to do it yourself (which amortized is on the same order of time), doing anything to seal up your object code is counterproductive.
Work to improve the code by revealing it, not by hiding it.
Unstated and implicit was: what if you lose the sour
Re:Maintainance nightmare (Score:2)
Normally, you would only do this after debugging your code. Obviously, it m
Re:Maintainance nightmare (Score:3, Interesting)
I had to decompile and patch a ridiculously buggy JDBC driver for a commercial database which had been run through an obfuscator, and ran into that issue. Renaming was rather a hassle, I must say.
I came to the conclusion that they had obfuscated their driver out of shame at the embarrasingly bad code, rather than to protect any intellectual property therein.
Re:Maintainance nightmare (Score:2)
Opposite of debugging (Score:4, Funny)
Hat tip to Jebediah Springfield.
Disagree (Score:2)
Re:Maintainance nightmare (Score:2)
Some user has in their
"That's not encrypted - that's a perl script I'm
working on." from crObar's now defunct matrix parody.
Consti-what? (Score:2, Funny)
I might have gone the bathroom, or perhaps had a snack. Maybe a nap.
Books online (Score:4, Informative)
And so I suggest a service like O'Reilly's Safari Bookshelf [oreilly.com]. It includes the full text of over 2,000 technical books, many not published by them. No killing trees, far less money than buying books, plus full text search.
Jad... (Score:5, Informative)
I have yet to try it on byte-code produced by non-Java languages, but I'd be interested to see the results...
(It sucks that it's no longer free. The version I've got I installed through Debian, for goodness sake, years ago. Does anyone know any free alternatives that work as well?)
Re:Jad... (Score:5, Informative)
Re:Jad... (Score:2)
It's the best java decompiler I have found.
Re:Jad... (Score:2, Informative)
Re:Jad... (Score:2)
Sun has this info for free... (Score:4, Informative)
Reverse engineering in Java is as simple as the compile process itself. Besides there are already free tools available so why bother??
Links to books on Amazon (Score:2)
Decompiling Java by Godfrey Nolan [amazon.com] on Amazon.
Another book on the subject is Covert Java : Techniques for Decompiling, Patching, and Reverse Engineering by Alex Kalinovsky [amazon.com]... probably more targetted at those who are already pretty familiar with things and want a more in-depth look.
(Yes, Slashbots, those are affiliate links... that doesn't make them any less useful though, does it?)
Re:Links to books on Amazon (Score:2, Insightful)
Yes, it does make them less useful. Because now it is impossible to tell whether you are saying things like "a more in-depth look" because you really mean it, or because you stand to make a quick buck by making bogus claims about the book.
Nothing personal, of course; you can probably see yourself why the rest of us simply can't know if you are being honest or running an astroturf con.
Nothing beats decompiling hacker code... (Score:3, Informative)
Its starts off with public variable names like:
public int YOU_DECOMPILING_NOOB =-1;
public int NO_SKILLZ_4U=100;
and then the obfusticator kicks in:
where a1 and al(with an L) are switched around.
The variable and method names look similar.
if (a1.b1.x.y == al.b1.xl.y2){
a1.v1.x.y &= al.b1.x1.y2 >> 0x4c;
a1.b1.x( al.b1.x2 );
}
Ouch! Also, I think every decompiler has some weaknesses and isn't able to undo all code. I know Jad has some limitations. Unfortunately, I wasn't able to get the source of the code that broke the decompilers
Why read a book. Just download Jode (Score:3, Informative)
on this topic, does anyone know how to: (Score:2)
By which I mean, there is a java applet running in my web browser. I'd like to decompile it and look over the source code. It's small enough I believe this would be informative. Is there a good way to do this?
Re:on this topic, does anyone know how to: (Score:2)
hmm (Score:2)
Want to keep your code to yourself? Use C++. (Score:3, Funny)
The books about decompiling Java are excellent advertisements for C++.
Or, another way to say it: (Score:2)
Advertisement: Want J. Random Hacker to fiddle with your code? Use Java.
Re:Want to keep your code to yourself? Use C++. (Score:3, Funny)
Enough obfuscation is equivalent to encryption. (Score:2)
The answer to Java decompilation is a write-once, read-whaaa? language.
Good obfuscation WORKS (Score:4, Informative)
Most obfuscators will make this track impossible, by doing things like using language keywords (while, for, if, and so on) for class/method/variable names, so that when you decompile the thing it cannot be recompiled. They also mix stuff around in the classfile enough so that figuring out what method is doing what becomes non-trivial -- stupid things mostly (like naming methods l1(), ll(), I1(), Il(), etc.), plus a few tricks to stop JAD from fully decompiling the class.
Enough of these little things add up to make the work involved in altering the decompiled class excessive and difficult.
The more sophisticated Java cracker doesn't bother. They decompile enough source to get their bearings, then edit the appropriate bytecode directly, with a classfile editor. Fortunately, most people with this level of experience can just pay for the frickin software they want.
I'm actually not obfuscating my Java code yet, but I'm going to start... it's just too easy to crack Java code without it. yGuard obfuscator [yworks.com] is pretty decent LGPL one, that can run as an Ant task.