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{{Short description|Process of extracting design information from anything artificial}}
{{More footnotes|date=January 2018}}
{{use dmy dates|date=November 2024}}
[[File:Tupolev Tu-4, Russia - Air Force AN0189663.jpg|thumb|The [[Tupolev Tu-4]], a [[Soviet Union|Soviet]] [[bomber]] built by reverse engineering captured [[Boeing B-29 Superfortress]]es]]
'''Reverse engineering''' (also known as '''backwards engineering''' or '''back engineering''') is a process or method through which one attempts to understand through [[deductive reasoning]] how a previously made device, process, system, or piece of [[software]] accomplishes a task with very little (if any) insight into exactly how it does so. Depending on the system under consideration and the technologies employed, the knowledge gained during reverse engineering can help with repurposing obsolete objects, doing security analysis, or learning how something works.<ref name=":0">{{Cite web |title=What is Reverse-engineering? How Does It Work |url=https://www.techtarget.com/searchsoftwarequality/definition/reverse-engineering |access-date=2022-07-27 |website=SearchSoftwareQuality |language=en}}</ref><ref>{{Cite web |title=Reverse Engineering |url=https://ethics.csc.ncsu.edu/intellectual/reverse/study.php |access-date=2022-07-27 |website=ethics.csc.ncsu.edu}}</ref><ref>{{Cite web |last=Garcia |first=Jorge |date=December 2015 |title=Un-building blocks: a model of reverse engineering and applicable heuristics |url=https://core.ac.uk/download/pdf/36740023.pdf |access-date=2023-06-04 |website=Core.ac.uk}}</ref>

Although the process is specific to the object on which it is being performed, all reverse engineering processes consist of three basic steps: information extraction, modeling, and review. Information extraction is the practice of gathering all relevant information for performing the operation. Modeling is the practice of combining the gathered information into an abstract model, which can be used as a guide for designing the new object or system. Review is the testing of the model to ensure the validity of the chosen abstract.<ref name=":0" /> Reverse engineering is applicable in the fields of [[computer engineering]], [[mechanical engineering]], [[design]], [[Electrical engineering|electrical]] and [[Electronic engineering|electronic]] engineering, [[civil engineering]], [[nuclear engineering]], [[aerospace engineering]], [[software engineering]], [[chemical engineering]],<ref>{{cite web |last1=Thayer |first1=Ken |title=How Does Reverse Engineering Work? |url=https://insights.globalspec.com/article/7367/how-does-reverse-engineering-work |website=globalspec |publisher=IEEE Global Spec |access-date=26 February 2018}}</ref> [[systems biology]]<ref>{{cite journal |last1=Villaverde |first1=Alejandro F. |last2=Banga |first2=Julio R. |title=Reverse engineering and identification in systems biology: strategies, perspectives and challenges |journal=Journal of the Royal Society Interface |date=6 February 2014 |volume=11 |issue=91 |page=20130505 |doi=10.1098/rsif.2013.0505 |pmid=24307566 |pmc=3869153}}</ref> and more.

==Overview==
There are many reasons for performing reverse engineering in various fields. Reverse engineering has its origins in the analysis of hardware for commercial or military advantage.<ref name="Chikofsky">{{cite journal |last1=Chikofsky |first1=E.J. |last2=Cross |first2=J.H. II |name-list-style=amp |title=Reverse Engineering and Design Recovery: A Taxonomy |journal=IEEE Software |volume=7 |issue=1 |pages=13–17 |year=1990 |doi=10.1109/52.43044|s2cid=16266661 }}</ref>{{rp|13}} However, the reverse engineering process may not always be concerned with creating a copy or changing the artifact in some way. It may be used as part of an [[analysis]] to [[Deductive reasoning|deduce]] design features from products with little or no additional knowledge about the procedures involved in their original production.<ref name="Chikofsky"/>{{rp|15}}

In some cases, the goal of the reverse engineering process can simply be a [[documentation|redocumentation]] of [[legacy systems]].<ref name="Chikofsky"/>{{rp|15}}<ref name="Nelson96">A Survey of Reverse Engineering and Program Comprehension. Michael L. Nelson, April 19, 1996, ODU CS 551&nbsp;– Software Engineering Survey.{{arxiv|cs/0503068v1}}</ref> Even when the reverse-engineered product is that of a competitor, the goal may not be to copy it but to perform [[competitor analysis]].<ref name="RajaFernandes2007">{{cite book |author1=Vinesh Raja |author2=Kiran J. Fernandes |title=Reverse Engineering: An Industrial Perspective |publisher=Springer Science & Business Media |year=2007 |page=3 |isbn=978-1-84628-856-2}}</ref> Reverse engineering may also be used to create [[interoperability|interoperable products]] and despite some narrowly-tailored United States and European Union legislation, the legality of using specific reverse engineering techniques for that purpose has been hotly contested in courts worldwide for more than two decades.<ref name="BandKatoh2011">{{cite book |author1=Jonathan Band |author2=Masanobu Katoh |title=Interfaces on Trial 2.0 |publisher=MIT Press |year=2011 |page=136 |isbn=978-0-262-29446-1}}</ref>

[[Software]] reverse engineering can help to improve the understanding of the underlying source code for the maintenance and improvement of the software. Relevant information can be extracted to make a decision for software development and graphical representations of the code can provide alternate views regarding the source code, which can help to detect and fix a [[software bug]] or vulnerability. Frequently, as some software develops, its design information and improvements are often lost over time, but that lost information can usually be recovered with reverse engineering. The process can also help to cut down the time required to understand the source code, thus reducing the overall cost of the software development.<ref name="IEEE 1990"/> Reverse engineering can also help to detect and to eliminate a malicious code written to the software with better code detectors. Reversing a source code can be used to find alternate uses of the source code, such as detecting the unauthorized replication of the source code where it was not intended to be used, or revealing how a competitor's product was built.<ref name="Eilam">{{cite book|author=Eilam, Eldad|title=Reversing: secrets of reverse engineering|publisher=John Wiley & Sons|year=2005|isbn=978-0-7645-7481-8}}</ref> That process is commonly used for [[Software cracking|"cracking" software and media]] to remove their [[copy protection]],<ref name="Eilam"/>{{rp|7}} or to create a possibly-improved [[copying|copy]] or even a [[Dupes|knockoff]], which is usually the goal of a competitor or a hacker.<ref name="Eilam"/>{{rp|8}}

[[Malware]] developers often use reverse engineering techniques to find vulnerabilities in an [[operating system]] to build a [[computer virus]] that can exploit the system vulnerabilities.<ref name="Eilam"/>{{rp|5}} Reverse engineering is also being used in [[cryptanalysis]] to find vulnerabilities in [[substitution cipher]], [[symmetric-key algorithm]] or [[public-key cryptography]].<ref name="Eilam"/>{{rp|6}}

There are other uses to reverse engineering:
*'''Games.''' Reverse engineering in the context of games and game engines is often used to understand underlying mechanics, data structures, and proprietary protocols, allowing developers to create [[Video game modding|mods]], custom tools, or to enhance compatibility. This practice is particularly useful when interfacing with existing systems to improve interoperability between different game components, engines, or platforms. Platforms like [https://Reshax.com Reshax] provide tools and resources that assist in analyzing game binaries, dissecting game engine behavior, thus contributing to a deeper understanding of game technology and enabling community-driven enhancements.
* '''Interfacing.''' Reverse engineering can be used when a system is required to interface to another system and how both systems would negotiate is to be established. Such requirements typically exist for [[interoperability]].
* '''Military or [[Industrial espionage|commercial]] [[espionage]].''' Learning about an enemy's or competitor's latest research by stealing or capturing a prototype and dismantling it may result in the development of a similar product or a better countermeasure against it.
* '''Obsolescence.''' [[Integrated circuits]] are often designed on proprietary systems and built on production lines, which become obsolete in only a few years. When systems using those parts can no longer be maintained since the parts are no longer made, the only way to incorporate the functionality into new technology is to reverse-engineer the existing chip and then to [[remake (computing)|redesign]] it using newer tools by using the understanding gained as a guide. Another obsolescence originated problem that can be solved by reverse engineering is the need to support (maintenance and supply for continuous operation) existing legacy devices that are no longer supported by their [[original equipment manufacturer]]. The problem is particularly critical in military operations.
* '''Product security analysis.''' That examines how a product works by determining the specifications of its components and estimate costs and identifies potential [[patent infringement]]. Also part of product security analysis is acquiring sensitive data by disassembling and analyzing the design of a system component.<ref name="rfc2828">Internet Engineering Task Force RFC 2828 Internet Security Glossary</ref> Another intent may be to remove [[copy protection]] or to circumvent access restrictions.
* '''Competitive technical intelligence.''' That is to understand what one's competitor is actually doing, rather than what it says that it is doing.
* '''Saving money.''' Finding out what a piece of electronics can do may spare a user from purchasing a separate product.
* '''[[Repurposing]].''' Obsolete objects are then reused in a different-but-useful manner.
* '''[[Design]].''' Production and design companies applied Reverse Engineering to practical craft-based manufacturing process. The companies can work on "historical" manufacturing collections through 3D scanning, 3D re-modeling and re-design. In 2013 Italian manufactures Baldi and [[Savio Firmino]] together with [[University of Florence]] optimized their innovation, design, and production processes.<ref>{{cite book|first1=Waldemar |last1=Karwowski|first2= Stefan |last2=Trzcielinski|first3=Beata|last3=Mrugalsk|first4=Massimo |last4=DiNicolantonio|first5=Emilio |last5=Rossi |title=Advances in Manufacturing, Production Management and Process Control|pages=287–288 |year=2018}}</ref>

== Common uses ==
===Machines===
As [[computer-aided design]] (CAD) has become more popular, reverse engineering has become a viable method to create a 3D virtual model of an existing physical part for use in 3D [[Computer-aided design|CAD]], [[Computer-aided manufacturing|CAM]], [[computer-aided engineering|CAE]], or other [[software]].<ref>{{cite journal |last1=Varady |first1=T |last2=Martin |first2=R |last3=Cox |first3=J |title=Reverse engineering of geometric models–an introduction |journal=Computer-Aided Design |doi=10.1016/S0010-4485(96)00054-1 |volume=29 |issue=4 |year=1997 |pages=255–268}}</ref> The reverse-engineering process involves measuring an object and then reconstructing it as a 3D model. The physical object can be measured using [[3D scanner|3D scanning]] technologies like [[coordinate-measuring machine|CMMs]], [[3D scanner#Triangulation|laser scanners]], [[3D scanner#Structured light|structured light digitizers]], or [[industrial CT scanning]] (computed tomography). The [[Measurement|measured]] [[data]] alone, usually represented as a [[point cloud]], lacks [[Topology|topological]] [[information]] and design intent. The former may be recovered by converting the point cloud to a triangular-faced [[mesh]]. Reverse engineering aims to go beyond producing such a mesh and to recover the design intent in terms of simple analytical surfaces where appropriate ([[Euclidean plane|planes]], [[cylinder]]s, etc.) as well as possibly [[Nonuniform rational B-spline|NURBS]] surfaces to produce a [[Boundary representation|boundary-representation]] CAD model. Recovery of such a model allows a design to be modified to meet new requirements, a manufacturing plan to be generated, etc.

Hybrid modeling is a commonly used term when NURBS and [[solid modeling|parametric modeling]] are implemented together. Using a combination of geometric and freeform surfaces can provide a powerful method of [[3D modeling]]. Areas of freeform data can be combined with exact geometric surfaces to create a hybrid model. A typical example of this would be the reverse engineering of a cylinder head, which includes freeform cast features, such as water jackets and high-tolerance machined areas.<ref>{{Cite web|url=http://www.physicaldigital.com/services/reverse-engineering/|title=Reverse Engineering|work=Physical Digital }}</ref>

Reverse engineering is also used by businesses to bring existing physical geometry into digital product development environments, to make a digital 3D record of their own products, or to assess competitors' products. It is used to analyze how a product works, what it does, what components it has; estimate costs; identify potential [[patent]] infringement; etc.

[[Value engineering]], a related activity that is also used by businesses, involves deconstructing and analyzing products. However, the objective is to find opportunities for cost-cutting.

===Printed circuit boards===
{{Main|PCB reverse engineering}}

Reverse engineering of [[printed circuit board]]s involves recreating fabrication data for a particular circuit board. This is done primarily to identify a design, and learn the functional and structural characteristics of a design. It also allows for the discovery of the design principles behind a product, especially if this design information is not easily available. 

Outdated PCBs are often subject to reverse engineering, especially when they perform highly critical functions such as powering machinery, or other electronic components. Reverse engineering these old parts can allow the reconstruction of the PCB if it performs some crucial task, as well as finding alternatives which provide the same function, or in upgrading the old PCB.<ref>{{Cite web |last=Patel |first=Suresh |date=2022-08-25 |title=Reverse Engineering a Printed Circuit Board |url=https://www.electronicdesign.com/markets/automation/article/21249478/mer-mar-electronics-reverse-engineering-a-printed-circuit-board |access-date=2024-02-01 |website=Electronic Design}}</ref>

Reverse engineering PCBs largely follow the same series of steps. First, images are created by drawing, scanning, or taking photographs of the PCB. Then, these images are ported to suitable reverse engineering software in order to create a rudimentary design for the new PCB. The quality of these images that is necessary for suitable reverse engineering is proportional to the complexity of the PCB itself. More complicated PCBs require well lighted photos on dark backgrounds, while fairly simple PCBs can be recreated simply with just basic dimensioning. Each layer of the PCB is carefully recreated in the software with the intent of producing a final design as close to the initial. Then, the schematics for the circuit are finally generated using an appropriate tool.<ref>{{Cite web |last=Patel |first=Suresh |date=2022-08-25 |title=Reverse Engineering a Printed Circuit Board |url=https://www.electronicdesign.com/markets/automation/article/21249478/mer-mar-electronics-reverse-engineering-a-printed-circuit-board |access-date=2024-02-01 |website=Electronic Design}}</ref>

===Software===
In 1990, the [[Institute of Electrical and Electronics Engineers]] (IEEE) defined (software) reverse engineering (SRE) as "the process of analyzing a
subject system to identify the system's components and their interrelationships and to create representations of the system in another form or at a higher
level of abstraction" in which the "subject system" is the end product of software development. Reverse engineering is a process of examination only, and the software system under consideration is not modified, which would otherwise be [[reengineering (software)|re-engineering]] or restructuring. Reverse engineering can be performed from any stage of the product cycle, not necessarily from the functional end product.<ref name="IEEE 1990"/>

There are two components in reverse engineering: redocumentation and design recovery. Redocumentation is the creation of new representation of the computer code so that it is easier to understand. Meanwhile, design recovery is the use of deduction or reasoning from general knowledge or personal experience of the product to understand the product's functionality fully.<ref name="IEEE 1990">{{Cite journal | last1 = Chikofsky | first1 = E. J. | last2 = Cross | first2 = J. H. | doi = 10.1109/52.43044 | title = Reverse engineering and design recovery: A taxonomy | journal = IEEE Software | volume = 7 | pages = 13–17 | date = January 1990 | s2cid = 16266661 | url = http://win.ua.ac.be/~lore/Research/Chikofsky1990-Taxonomy.pdf | access-date = 2012-07-02 | archive-url = https://web.archive.org/web/20180417124021/http://win.ua.ac.be/~lore/Research/Chikofsky1990-Taxonomy.pdf | archive-date = 2018-04-17  }}</ref> It can also be seen as "going backwards through the development cycle".<ref>{{cite book | last=Warden | first=R. | title=Software Reuse and Reverse Engineering in Practice | year=1992 | publisher=Chapman & Hall | location=London, England | pages=283–305}}</ref> In this model, the output of the implementation phase (in source code form) is reverse-engineered back to the analysis phase, in an inversion of the traditional [[waterfall model]]. Another term for this technique is [[program comprehension]].<ref name="Nelson96"/> The Working Conference on Reverse Engineering (WCRE) has been held yearly to explore and expand the techniques of reverse engineering.<ref name="Eilam"/><ref>{{cite web|title=Working Conference on Reverse Engineering (WCRE)|url=http://dblp.uni-trier.de/db/conf/wcre/index.html|website=uni-trier.de|publisher=Computer Science bibliography|access-date=22 February 2018|archive-url=https://web.archive.org/web/20170314150255/http://dblp.uni-trier.de/db/conf/wcre/index.html|archive-date=14 March 2017}}</ref> [[Computer-aided software engineering]] (CASE) and automated code generation have contributed greatly in the field of reverse engineering.<ref name="Eilam"/>

[[Software anti-tamper]] technology like [[obfuscation (software)|obfuscation]] is used to deter both reverse engineering and re-engineering of proprietary software and software-powered systems. In practice, two main types of reverse engineering emerge. In the first case, source code is already available for the software, but higher-level aspects of the program, which are perhaps poorly documented or documented but no longer valid, are discovered. In the second case, there is no source code available for the software, and any efforts towards discovering one possible source code for the software are regarded as reverse engineering. The second usage of the term is more familiar to most people. Reverse engineering of software can make use of the [[clean room design]] technique to avoid copyright infringement.

On a related note, [[black box testing]] in [[software engineering]] has a lot in common with reverse engineering. The tester usually has the [[application programming interface|API]] but has the goals to find bugs and undocumented features by bashing the product from outside.<ref>{{cite book | title=Reverse Engineering and Testing of Black-Box Software Components: by Grammatical Inference techniques | publisher=LAP LAMBERT Academic Publishing | author=Shahbaz, Muzammil | year=2012 | isbn=978-3-659-14073-0}}</ref>

Other purposes of reverse engineering include security auditing, removal of copy protection ("[[software cracking|cracking]]"), circumvention of access restrictions often present in [[consumer electronics]], customization of [[embedded systems]] (such as engine management systems), in-house repairs or retrofits, enabling of additional features on low-cost "crippled" hardware (such as some graphics card chip-sets), or even mere satisfaction of curiosity.

====Binary software====
Binary reverse engineering is performed if source code for a software is unavailable.<ref name="Eilam"/> This process is sometimes termed ''reverse code engineering'', or RCE.<ref>{{cite book | last=Chuvakin | first=Anton |author2=Cyrus Peikari | edition=1st | title=Security Warrior | url=http://www.oreilly.com/catalog/swarrior/reviews.html | access-date=2006-05-25 | publisher=O'Reilly | date=January 2004  | archive-url=https://web.archive.org/web/20060522102255/http://www.oreilly.com/catalog/swarrior/reviews.html | archive-date=2006-05-22}}</ref> For example, decompilation of binaries for the [[Java platform]] can be accomplished by using Jad. One famous case of reverse engineering was the first non-[[IBM]] implementation of the [[IBM PC|PC]] [[BIOS]], which launched the historic [[IBM PC compatible]] industry that has been the overwhelmingly-dominant [[computer hardware]] platform for many years. Reverse engineering of software is protected in the US by the [[fair use]] exception in [[copyright law]].<ref>{{Cite journal |doi=10.2307/797533 |author-link=Pamela Samuelson |first1=Pamela |last1=Samuelson |name-list-style=amp |first2=Suzanne |last2=Scotchmer |title=The Law and Economics of Reverse Engineering |volume=111 |journal=[[Yale Law Journal]] |issue=7 |pages=1575–1663 |year=2002 |url=http://www.yalelawjournal.org/the-yale-law-journal/content-pages/the-law-and-economics-of-reverse-engineering/ |jstor=797533 |access-date=2011-10-31 |archive-url=https://web.archive.org/web/20100715135359/http://yalelawjournal.org/the-yale-law-journal/content-pages/the-law-and-economics-of-reverse-engineering/ |archive-date=2010-07-15  }}</ref> The [[Samba software]], which allows systems that do not run [[Microsoft Windows]] systems to share files with systems that run it, is a classic example of software reverse engineering<ref>{{cite web | title=Samba: An Introduction | url=http://www.samba.org/samba/docs/SambaIntro.html | date=2001-11-27 | access-date=2009-05-07}}</ref> since the Samba project had to reverse-engineer unpublished information about how Windows file sharing worked so that non-Windows computers could emulate it. The [[Wine (software)|Wine]] project does the same thing for the [[Windows API]], and [[OpenOffice.org]] is one party doing that for the [[Microsoft Office]] file formats. The [[ReactOS]] project is even more ambitious in its goals by striving to provide binary (ABI and API) compatibility with the current Windows operating systems of the NT branch, which allows software and drivers written for Windows to run on a clean-room reverse-engineered [[free software]] ([[GPL]]) counterpart.

=====Binary software techniques=====
Reverse engineering of software can be accomplished by various methods.
The three main groups of software reverse engineering are
#Analysis through observation of information exchange, most prevalent in protocol reverse engineering, which involves using [[bus analyzer]]s and [[packet sniffer]]s, such as for accessing a [[computer bus]] or [[computer network]] connection and revealing the traffic data thereon. Bus or network behavior can then be analyzed to produce a standalone implementation that mimics that behavior. That is especially useful for reverse engineering [[device driver]]s. Sometimes, reverse engineering on [[embedded system]]s is greatly assisted by tools deliberately introduced by the manufacturer, such as [[JTAG]] ports or other debugging means. In [[Microsoft Windows]], low-level debuggers such as [[SoftICE]] are popular.
#[[Disassembly]] using a [[disassembler]], meaning the raw [[machine language]] of the program is read and understood in its own terms, only with the aid of machine-language [[mnemonic]]s. It works on any computer program but can take quite some time, especially for those who are not used to machine code. The [[Interactive Disassembler]] is a particularly popular tool.
#Decompilation using a [[decompiler]], a process that tries, with varying results, to recreate the source code in some high-level language for a program only available in machine code or [[bytecode]].

====Software classification====
Software classification is the process of identifying similarities between different software binaries (such as two different versions of the same binary) used to detect code relations between software samples. The task was traditionally done manually for several reasons (such as patch analysis for vulnerability detection and [[copyright infringement]]), but it can now be done somewhat automatically for large numbers of samples.

This method is being used mostly for long and thorough reverse engineering tasks (complete analysis of a complex algorithm or big piece of software). In general, [[statistical classification]] is considered to be a hard problem, which is also true for software classification, and so few solutions/tools that handle this task well.

===Source code===
A number of [[Unified Modeling Language|UML]] tools refer to the process of importing and analysing source code to generate UML diagrams as "reverse engineering" {{xref|(see: [[List of Unified Modeling Language tools]])}}.

Although UML is one approach in providing "reverse engineering" more recent advances in international standards activities have resulted in the development of the [[Knowledge Discovery Metamodel]] (KDM). The standard delivers an ontology for the intermediate (or abstracted) representation of programming language constructs and their interrelationships. An [[Object Management Group]] standard (on its way to becoming an ISO standard as well),{{citation needed|date=July 2023}} KDM has started to take hold in industry with the development of tools and analysis environments that can deliver the extraction and analysis of source, binary, and byte code. For source code analysis, KDM's granular standards' architecture enables the extraction of software system flows (data, control, and call maps), architectures, and business layer knowledge (rules, terms, and process). The standard enables the use of a common data format (XMI) enabling the correlation of the various layers of system knowledge for either detailed analysis (such as root cause, impact) or derived analysis (such as business process extraction). Although efforts to represent language constructs can be never-ending because of the number of languages, the continuous evolution of software languages, and the development of new languages, the standard does allow for the use of extensions to support the broad language set as well as evolution. KDM is compatible with UML, BPMN, RDF, and other standards enabling migration into other environments and thus leverage system knowledge for efforts such as software system transformation and enterprise business layer analysis.

===Protocols===
[[Communications protocol|Protocols]] are sets of rules that describe message formats and how messages are exchanged: the protocol [[finite-state machine|state machine]]. Accordingly, the problem of protocol reverse-engineering can be partitioned into two subproblems: message format and state-machine reverse-engineering.

The message formats have traditionally been reverse-engineered by a tedious manual process, which involved analysis of how protocol implementations process messages, but recent research proposed a number of automatic solutions.<ref>W. Cui, J. Kannan, and H. J. Wang. Discoverer: Automatic protocol reverse engineering from network traces. In Proceedings of 16th USENIX Security Symposium on USENIX Security Symposium, pp. 1–14.</ref><ref>W. Cui, M. Peinado, K. Chen, H. J. Wang, and L. Irún-Briz. Tupni: Automatic reverse engineering of input formats. In Proceedings of the 15th ACM Conference on Computer and Communications Security, pp. 391–402. ACM, Oct 2008.</ref><ref name="M. Comparetti, G. Wondracek pages 110-125">P. M. Comparetti, G. Wondracek, C. Kruegel, and E. Kirda. Prospex: Protocol specification extraction. In Proceedings of the 2009 30th IEEE Symposium on Security and Privacy, pp. 110–125, Washington, 2009. IEEE Computer Society.</ref> Typically, the automatic approaches group observe messages into clusters by using various [[cluster analysis|clustering analyses]], or they emulate the protocol implementation tracing the message processing.

There has been less work on reverse-engineering of state-machines of protocols. In general, the protocol state-machines can be learned either through a process of [[offline learning]], which passively observes communication and attempts to build the most general state-machine accepting all observed sequences of messages, and [[online machine learning|online learning]], which allows interactive generation of probing sequences of messages and listening to responses to those probing sequences. In general, offline learning of small state-machines is known to be [[NP-complete]],<ref>{{cite journal|doi=10.1016/S0019-9958(78)90562-4|title=Complexity of automaton identification from given data|year=1978|last1=Gold|first1=E|journal=Information and Control|volume=37|issue=3|pages=302–320 |doi-access=free}}</ref> but online learning can be done in polynomial time.<ref>{{cite journal|author=D. Angluin|title= Learning regular sets from queries and counterexamples|doi=10.1016/0890-5401(87)90052-6|journal= Information and Computation|volume= 75|issue=2|pages=87–106|year=1987|doi-access=free}}</ref> An automatic offline approach has been demonstrated by Comparetti et al.<ref name="M. Comparetti, G. Wondracek pages 110-125"/> and an online approach by Cho et al.<ref>C.Y. Cho, D. Babic, R. Shin, and D. Song. {{usurped|1=[https://web.archive.org/web/20101028102651/http://www.domagoj-babic.com/index.php/Pubs/CCS10botnets Inference and Analysis of Formal Models of Botnet Command and Control Protocols]}}, 2010 ACM Conference on Computer and Communications Security.</ref>

Other components of typical protocols, like encryption and hash functions, can be reverse-engineered automatically as well. Typically, the automatic approaches trace the execution of protocol implementations and try to detect buffers in memory holding unencrypted packets.<ref>[http://bitblaze.cs.berkeley.edu/papers/polyglot_ccs07_av.pdf Polyglot: automatic extraction of protocol message format using dynamic binary analysis]. J. Caballero, H. Yin, Z. Liang, and D. Song. Proceedings of the 14th ACM conference on Computer and communications security, pp. 317–329.</ref>

===Integrated circuits/smart cards===
Reverse engineering is an invasive and destructive form of analyzing a [[smart card]]. The attacker uses chemicals to etch away layer after layer of the smart card and takes pictures with a [[scanning electron microscope]] (SEM). That technique can reveal the complete hardware and software part of the smart card. The major problem for the attacker is to bring everything into the right order to find out how everything works. The makers of the card try to hide keys and operations by mixing up memory positions, such as by bus scrambling.<ref>Wolfgang Rankl, Wolfgang Effing, Smart Card Handbook (2004)</ref><ref>T. Welz: [http://www.crypto.rub.de/its_seminar_ws0708.html Smart cards as methods for payment]{{dead link|date=May 2023|bot=medic}}{{cbignore|bot=medic}} (2008), Seminar ITS-Security Ruhr-Universität Bochum</ref>

In some cases, it is even possible to attach a probe to measure voltages while the smart card is still operational. The makers of the card employ sensors to detect and prevent that attack.<ref>David C. Musker: [http://www.jenkins.eu/articles-general/reverse-engineering.asp Protecting & Exploiting Intellectual Property in Electronics] {{Webarchive|url=https://web.archive.org/web/20110709001411/http://www.jenkins.eu/articles-general/reverse-engineering.asp |date=2011-07-09 }}, IBC Conferences, 10 June 1998</ref> That attack is not very common because it requires both a large investment in effort and special equipment that is generally available only to large chip manufacturers. Furthermore, the payoff from this attack is low since other security techniques are often used such as shadow accounts. It is still uncertain whether attacks against chip-and-PIN cards to replicate encryption data and then to crack PINs would provide a cost-effective attack on multifactor authentication.

Full reverse engineering proceeds in several major steps.

The first step after images have been taken with a SEM is stitching the images together, which is necessary because each layer cannot be captured by a single shot. A SEM needs to sweep across the area of the circuit and take several hundred images to cover the entire layer. Image stitching takes as input several hundred pictures and outputs a single properly-overlapped picture of the complete layer.

Next, the stitched layers need to be aligned because the sample, after etching, cannot be put into the exact same position relative to the SEM each time. Therefore, the stitched versions will not overlap in the correct fashion, as on the real circuit. Usually, three corresponding points are selected, and a transformation applied on the basis of that.

To extract the circuit structure, the aligned, stitched images need to be segmented, which highlights the important circuitry and separates it from the uninteresting background and insulating materials.

Finally, the wires can be traced from one layer to the next, and the netlist of the circuit, which contains all of the circuit's information, can be reconstructed.

===Military applications===
{{more citations needed section|date=July 2014}}
Reverse engineering is often used by people to copy other nations' technologies, devices, or information that have been obtained by regular troops in the fields or by [[military intelligence|intelligence]] operations. It was often used during the [[Second World War]] and the [[Cold War]]. Following are some well known examples from the Second World War and afterward:
* [[Jerry can]]: British and American forces in [[WW2]] noticed that the Germans had gasoline cans with an excellent design. They reverse-engineered copies of those cans, which were popularly known as "Jerry cans".
* [[Nakajima G5N]]: In 1939, the U.S. [[Douglas Aircraft Company]] sold its [[Douglas DC-4E|DC-4E]] airliner prototype to [[Imperial Japanese Airways]], which was secretly acting as a front for the [[Imperial Japanese Navy]], which wanted a long-range [[strategic bomber]] but had been hindered by the Japanese aircraft industry's inexperience with heavy long-range aircraft. The DC-4E was transferred to the [[Nakajima Aircraft Company]] and dismantled for study; as a cover story, the Japanese press reported that it had crashed in [[Tokyo Bay]].<ref>{{cite book |last=Francillon |first=René J. |title=McDonnell Douglas Aircraft since 1920 |volume=1 |location=Annapolis, Maryland |publisher=Naval Institute Press |edition=2nd |date=1988 |orig-date=1979 |pages=265–268|isbn=0-87021-428-4 }}</ref><ref>{{cite journal |last=Westell |first=Freeman |title=Big Iron, big engines & bigger headaches: Building the first experimental strategic bombers|journal=Airpower |volume=29 |issue=6 |date=November 1999 |pages=18, 49–50}}</ref> The wings, engines, and [[landing gear]] of the G5N were copied directly from the DC-4E.<ref>{{cite book |last1=Angelucci |first1=Enzo |last2=Matricardi |first2=Paolo |title=-World War II Airplanes: Volume 2 |location=Chicago |publisher=Rand McNally & Company |date=1978 |isbn=0-528-88171-X |page=127}}</ref>
*[[Panzerschreck]]: The Germans captured an American [[bazooka]] during the Second World War and reverse engineered it to create the larger Panzerschreck.
* [[Tupolev Tu-4]]: In 1944, three American [[B-29 Superfortress|B-29]] bombers on missions over [[Japan]] were forced to land in the [[Soviet Union]]. The Soviets, who did not have a similar strategic bomber, decided to copy the B-29. Within three years, they had developed the Tu-4, a nearly-perfect copy.<ref>Yeam Gordon and Vladimir Rigmant, Tupolev Tu-4: Soviet Superfortress (Hinckley, U.K.: Midland, 2002).</ref>
* [[SCR-584 radar]]: copied by the Soviet Union after the Second World War, it is known for a few modifications - СЦР-584, Бинокль-Д.
* [[V-2]] rocket: Technical documents for the V-2 and related technologies were captured by the Western Allies at the end of the war. The Americans focused their reverse engineering efforts via [[Operation Paperclip]], which led to the development of the [[PGM-11 Redstone]] rocket.<ref>{{cite web|url=http://www.centennialofflight.net/essay/Dictionary/REDSTONE/DI149.htm |title=Redstone rocket |publisher=centennialofflight.net |access-date=2010-04-27}}</ref> The Soviets used captured German engineers to reproduce technical documents and plans and worked from captured hardware to make their clone of the rocket, the [[R-1 (missile)|R-1]]. Thus began the postwar Soviet rocket program, which led to the [[R-7 Semyorka|R-7]] and the beginning of the [[space race]].
* [[Vympel K-13|K-13/R-3S]] missile ([[NATO reporting name]] AA-2 Atoll), a Soviet reverse-engineered copy of the [[AIM-9 Sidewinder]], was made possible after a Taiwanese (ROCAF) AIM-9B hit a Chinese PLA [[MiG-17]] without exploding in September 1958.<ref>"The Chinese Air Force: Evolving Concepts, Roles, and Capabilities", Center for the Study of Chinese Military Affairs (U.S), by National Defense University Press, p. 277</ref> The missile became lodged within the airframe, and the pilot returned to base with what Soviet scientists would describe as a university course in missile development.
* [[BGM-71 TOW|Toophan]] missile: In May 1975, negotiations between Iran and Hughes Missile Systems on co-production of the [[BGM-71 TOW]] and Maverick missiles stalled over disagreements in the pricing structure, the subsequent [[1979 revolution]] ending all plans for such co-production. Iran was later successful in reverse-engineering the missile and now produces its own copy, the Toophan.
* China has [[intellectual property in the People's Republic of China|reverse engineered many examples]] of Western and Russian hardware, from fighter aircraft to missiles and [[HMMWV]] cars, such as the MiG-15,17,19,21 (which became the J-2,5,6,7) and the Su-33 (which became the J-15).<ref>Chandrashekar, S., R. Nagappa, L. Sundaresan, and N. Ramani. 2011. Technology & Innovation in China: A Case Study of Single Crystal Superalloy Development for Aircraft Turbine Blades, R4–11. ISSSP National Institute of Advanced Studies, Bangalore. http://isssp.in/wp-content/uploads/2013/01/Technology-and-Innovation-in-China-A-case-Study-of-Single-Crystal4.pdf; and Dillon Zhou, "China J-15 Fighter Jet: Chinese Officials Defend New Fighter As Chinese Original, but Questions Remain," Mic, December 16, 2012, https://mic.com/articles/20270/china-j-15-fighter-jet-chinese-officials-defend-new-fighter-{{Dead link|date=December 2022 |bot=InternetArchiveBot |fix-attempted=yes }} as-chinese-original-but-questions-remain</ref>
* During the Second World War, Polish and British cryptographers studied captured German "[[cryptanalysis of the Enigma|Enigma]]" message encryption machines for weaknesses. Their operation was then simulated on electromechanical devices, "[[bombe]]s", which tried all the possible scrambler settings of the "Enigma" machines that helped the breaking of coded messages that had been sent by the Germans.
* Also during the Second World War, British scientists analyzed and defeated a [[Battle of the Beams|series of increasingly-sophisticated radio navigation systems]] used by the [[Luftwaffe]] to perform guided bombing missions at night. The British countermeasures to the system were so effective that in some cases, German aircraft were led by signals to land at [[RAF]] bases since they believed that they had returned to German territory.

===Gene networks ===
Reverse engineering concepts have been applied to [[biology]] as well, specifically to the task of understanding the structure and function of [[gene regulatory network]]s. They regulate almost every aspect of biological behavior and allow cells to carry out physiological processes and responses to perturbations. Understanding the structure and the dynamic behavior of gene networks is therefore one of the paramount challenges of systems biology, with immediate practical repercussions in several applications that are beyond basic research.<ref name="Giorgi2020">{{cite journal|last1=Giorgi|first1=Federico M.|title=Gene network reverse engineering: The Next Generation|journal=Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms|volume=1863|issue=6|year=2020|page=194523|issn=1874-9399|doi=10.1016/j.bbagrm.2020.194523|pmid=32145356|hdl=11585/753853 |s2cid=212629142}}</ref>

There are several methods for reverse engineering gene regulatory networks by using molecular biology and data science methods. They have been generally divided into six classes:<ref name="Mercatelli_2020">{{cite journal|last1=Mercatelli|first1=Daniele|last2=Scalambra|first2=Laura|last3=Triboli|first3=Luca|last4=Ray|first4=Forest|last5=Giorgi|first5=Federico M.|title=Gene regulatory network inference resources: A practical overview|journal=Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms|volume=1863|issue=6|year=2020|page=194430|issn=1874-9399|doi=10.1016/j.bbagrm.2019.194430|pmid=31678629|s2cid=207895066}}</ref>

[[File:Gene network inference classes.png|thumb|The six classes of gene network inference methods, according to<ref name="Mercatelli_2020" />]]
* Coexpression methods are based on the notion that if two genes exhibit a similar expression profile, they may be related although no causation can be simply inferred from coexpression.
* Sequence motif methods analyze gene promoters to find specific [[transcription factor]] [[binding domain]]s. If a transcription factor is predicted to bind a promoter of a specific gene, a regulatory connection can be hypothesized.
* [[Chromatin immunoprecipitation|Chromatin ImmunoPrecipitation]] (ChIP) methods investigate the [[genome]]-wide profile of [[DNA-binding domain|DNA binding]] of chosen transcription factors to infer their downstream gene networks.
* Orthology methods transfer gene network knowledge from one species to another.
* Literature methods implement [[text mining]] and manual research to identify putative or experimentally-proven gene network connections.
* Transcriptional complexes methods leverage information on protein-protein interactions between transcription factors, thus extending the concept of gene networks to include transcriptional regulatory complexes.

Often, gene network reliability is tested by genetic perturbation experiments followed by dynamic modelling, based on the principle that removing one network node has predictable effects on the functioning of the remaining nodes of the network.<ref name="TegnerYeung2003">{{cite journal|last1=Tegner|first1=J.|last2=Yeung|first2=M. K. S.|last3=Hasty|first3=J.|last4=Collins|first4=J. J.|title=Reverse engineering gene networks: Integrating genetic perturbations with dynamical modeling|journal=Proceedings of the National Academy of Sciences|volume=100|issue=10|year=2003|pages=5944–5949|issn=0027-8424|doi=10.1073/pnas.0933416100|pmid=12730377|pmc=156306|bibcode=2003PNAS..100.5944T|doi-access=free}}</ref>
Applications of the reverse engineering of gene networks range from understanding mechanisms of plant physiology<ref name="FriedelUsadel2012">{{cite journal|last1=Friedel|first1=Swetlana|last2=Usadel|first2=Björn|last3=von Wirén|first3=Nicolaus|last4=Sreenivasulu|first4=Nese|title=Reverse Engineering: A Key Component of Systems Biology to Unravel Global Abiotic Stress Cross-Talk|journal=Frontiers in Plant Science|volume=3|year=2012|page=294|issn=1664-462X|doi=10.3389/fpls.2012.00294|pmid=23293646|pmc=3533172|doi-access=free}}</ref> to the highlighting of new targets for anticancer therapy.<ref name="LefebvreRieckhof2012">{{cite journal|last1=Lefebvre|first1=Celine|last2=Rieckhof|first2=Gabrielle|last3=Califano|first3=Andrea|title=Reverse-engineering human regulatory networks|journal=Wiley Interdisciplinary Reviews: Systems Biology and Medicine|volume=4|issue=4|year=2012|pages=311–325|issn=1939-5094|doi=10.1002/wsbm.1159|pmid=22246697|pmc=4128340}}</ref>

===Overlap with patent law===
Reverse engineering applies primarily to gaining understanding of a process or artifact in which the manner of its construction, use, or internal processes has not been made clear by its creator.

[[Patent]]ed items do not of themselves have to be reverse-engineered to be studied, for the essence of a patent is that inventors provide a detailed public disclosure themselves, and in return receive [[Intellectual property rights|legal protection]] of the [[invention]] that is involved. However, an item produced under one or more patents could also include other technology that is not patented and not disclosed. Indeed, one common motivation of reverse engineering is to determine whether a competitor's product contains [[patent infringement]] or [[copyright infringement]].

==Legality==
===United States===
In the United States, even if an artifact or process is protected by [[trade secrets]], reverse-engineering the artifact or process is often lawful if it has been legitimately obtained.<ref>[https://www.asme.org/career-education/articles/management-professional-practice/trade-secrets-101 "Trade Secrets 101", Feature Article, March 2011]. ASME. Retrieved on 2013-10-31.</ref>

Reverse engineering of [[computer software]] often falls under both [[contract law]] as a [[breach of contract]] as well as any other relevant laws. That is because most [[EULA|end-user license agreements]] specifically prohibit it, and US courts have ruled that if such terms are present, they override the copyright law that expressly permits it (see ''[[Bowers v. Baystate Technologies]]''<ref>[http://www.utsystem.edu/ogc/intellectualproperty/baystatevbowersdiscussion.htm Baystate v. Bowers Discussion]. Utsystem.edu. Retrieved on 2011-05-29.</ref><ref>Gross, Grant. (2003-06-26) [http://www.infoworld.com/d/developer-world/contract-case-could-hurt-reverse-engineering-337 Contract case could hurt reverse engineering {{!}} Developer World]. InfoWorld. Retrieved on 2011-05-29.</ref>). According to Section 103(f) of the [[Digital Millennium Copyright Act]] ([https://www.law.cornell.edu/uscode/text/17/1201- 17 U.S.C. § 1201 (f)]), a person in legal possession of a program may reverse-engineer and circumvent its protection if that is necessary to achieve "interoperability", a term that broadly covers other devices and programs that can interact with it, make use of it, and to use and transfer data to and from it in useful ways. A limited exemption exists that allows the knowledge thus gained to be shared and used for interoperability purposes.{{efn|The section states:<br />(f) Reverse Engineering.—<br />(1) Notwithstanding the provisions of subsection (a)(1)(A), a person who has lawfully obtained the right to use a copy of a computer program may circumvent a technological measure that effectively controls access to a particular portion of that program for the sole purpose of identifying and analyzing those elements of the program that are necessary to achieve interoperability of an independently created computer program with other programs, and that have not previously been readily available to the person engaging in the circumvention, to the extent any such acts of identification and analysis do not constitute infringement under this title.<br />(2) Notwithstanding the provisions of subsections (a)(2) and (b), a person may develop and employ technological means to circumvent a technological measure, or to circumvent protection afforded by a technological measure, in order to enable the identification and analysis under paragraph (1), or for the purpose of enabling interoperability of an independently created computer program with other programs, if such means are necessary to achieve such interoperability, to the extent that doing so does not constitute infringement under this title.<br />(3) The information acquired through the acts permitted under paragraph (1), and the means permitted under paragraph (2), may be made available to others if the person referred to in paragraph (1) or (2), as the case may be, provides such information or means solely for the purpose of enabling interoperability of an independently created computer program with other programs, and to the extent that doing so does not constitute infringement under this title or violate applicable law other than this section.<br />(4) For purposes of this subsection, the term 「interoperability」 means the ability of computer programs to exchange information, and of such programs mutually to use the information which has been exchanged.}}

===European Union===
[[Computer Programs Directive|EU Directive 2009/24]] on the legal protection of computer programs, which superseded an earlier (1991) directive,<ref>{{CELEX|id=01991L0250-19931119|text=Council Directive 91/250/EEC of 14 May 1991 on the legal protection of computer programs}}</ref> governs reverse engineering in countries of the [[European Union]].<ref>{{CELEX|id=32009L0024|text=Directive 2009/24/EC of the European Parliament and of the Council of 23 April 2009 on the legal protection of computer programs (Codified version)}}</ref>{{efn|The directive states:{{quote|The unauthorised reproduction, translation, adaptation or transformation of the form of the code in which a copy of a computer program has been made available constitutes an infringement of the exclusive rights of the author. Nevertheless, circumstances may exist when such a reproduction of the code and translation of its form are indispensable to obtain the necessary information to achieve the interoperability of an independently created program with other programs. It has therefore to be considered that, in these limited circumstances only, performance of the acts of reproduction and translation by or on behalf of a person having a right to use a copy of the program is legitimate and compatible with fair practice and must therefore be deemed not to require the authorisation of the rightholder. An objective of this exception is to make it possible to connect all components of a computer system, including those of different manufacturers, so that they can work together. Such an exception to the author's exclusive rights may not be used in a way which prejudices the legitimate interests of the rightholder or which conflicts with a normal exploitation of the program.}}}}

== See also ==
* {{annotated link|AI-assisted reverse engineering}}
* {{annotated link|Antikythera mechanism}}
* {{annotated link|Backward induction}}
* {{annotated link|Benchmarking}}
* {{annotated link|Bus analyzer}}
* {{annotated link|Chonda}}
* {{annotated link|Clone (computing)}}
* {{annotated link|Clean room design}}
* {{annotated link|coordinate-measuring machine|Coordinate-measuring machine (CMM)}}
* {{annotated link|Code morphing}}
* [[Connectix Virtual Game Station]]
* {{annotated link|Counterfeiting}}
* {{annotated link|Cryptanalysis}}
* {{annotated link|Decompile}}
* {{annotated link|Deformulation}}
* {{annotated link|Digital Millennium Copyright Act|Digital Millennium Copyright Act (DMCA)}}
* {{annotated link|Disassembler}}
* {{annotated link|Dongle}}
* {{annotated link|Forensic engineering}}
* {{annotated link|Industrial CT scanning}}
* {{annotated link|Interactive Disassembler}}
* {{annotated link|Knowledge Discovery Metamodel}}
* {{annotated link|3D scanner#Triangulation|Laser scanner}}
* [[List of production topics]]
* {{annotated link|Listeroid#Listeroid engines|Listeroid Engines}}
* {{annotated link|Logic analyzer}}
* {{annotated link|Paycheck (film)|''Paycheck'' (film)}}
* {{annotated link|Repurposing}}
* {{annotated link|Thought experiment#Retrodiction|Retrodiction (Thought experimentation)}}
* {{annotated link|Reverse architecture}}
* {{annotated link|Round-trip engineering}}
* {{annotated link|Sega v. Accolade|''Sega v. Accolade''}}
* {{annotated link|Software archaeology}}
* {{annotated link|Software cracking}}
* {{annotated link|Value engineering}}

== Notes ==
{{notes}}

== References ==
{{reflist}}

==Sources==
{{div col|colwidth=30em}}
* {{cite book |title=Reversing: Secrets of Reverse Engineering |last=Eilam |first=Eldad |year=2005 |publisher=[[Wiley Publishing]] |isbn=978-0-7645-7481-8 |page=595 |title-link=Reversing: Secrets of Reverse Engineering}}
* Elvidge, Julia, "Using Reverse Engineering to Discover Patent Infringement," Chipworks, Sept. 2010. Online: http://www.photonics.com/Article.aspx?AID=44063
* {{cite web |url=http://www.reversingproject.info |author=Cipresso, Teodoro |title=Software Reverse Engineering Education |access-date=2009-08-22 |work=SJSU Master's Thesis |year=2009}}
* [[Hausi A. Muller|Hausi A. Müller]] and Holger M. Kienle, "A Small Primer on Software Reverse Engineering," Technical Report, University of Victoria, 17 pages, March 2009. Online: http://holgerkienle.wikispaces.com/file/view/MK-UVic-09.pdf
* Heines, Henry, "Determining Infringement by X-Ray Diffraction," ''Chemical Engineering Process'', Jan. 1999 (example of reverse engineering used to detect IP infringement)
* {{Cite book |title=Hacking the Xbox: An Introduction to Reverse Engineering | last=Huang | first=Andrew |year=2003 |publisher=[[No Starch Press]] |isbn=978-1-59327-029-2}}
* {{cite web |url=http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=11966 |author=James, Dick |title=Reverse Engineering Delivers Product Knowledge; Aids Technology Spread |access-date=2009-02-03 |work=Electronic Design |publisher=Penton Media, Inc |date=January 19, 2006}}
* {{Cite book |title=Reverse Engineering: Mechanisms, Structures, Systems & Materials | last=Messler | first=Robert |year=2013 |publisher=[[McGraw Hill]] |isbn=978-0-07-182516-0}} (introduction to hardware teardowns, including methodology, goals)
* {{Cite book |title=Reverse Engineering – An Industrial Perspective |last=Raja |first=Vinesh |author2=Fernandes, Kiran J. |year=2008 |publisher = [[Springer Science+Business Media|Springer]] |isbn=978-1-84628-855-5 |page=242}}
* [[Pamela Samuelson|Samuelson, Pamela]] and Scotchmer, Suzanne, "The Law and Economics of Reverse Engineering," 111 Yale L.J. 1575 (2002). Online: http://people.ischool.berkeley.edu/~pam/papers/l&e%20reveng3.pdf
* {{cite book |author-first1=Andrew |author-last1=Schulman |author-first2=Ralf D. |author-last2=Brown |author-link2=Ralf D. Brown |author-first3=David |author-last3=Maxey |author-first4=Raymond J. |author-last4=Michels |author-first5=Jim |author-last5=Kyle |title=Undocumented DOS: A programmer's guide to reserved MS-DOS functions and data structures - expanded to include MS-DOS 6, Novell DOS and Windows 3.1 |publisher=[[Addison Wesley]] |edition=2 |date=1994 |orig-date=November 1993<!-- first printing --> |isbn=0-201-63287-X |location=Reading, Massachusetts |pages=[https://archive.org/details/undocumenteddosp00andr_0/page/229 229–241] |url-access=registration |url=https://archive.org/details/undocumenteddosp00andr_0/page/229}} (xviii+856+vi pages, 3.5"-floppy) Errata: {{usurped|1=[https://web.archive.org/web/20190417215556/http://www.cs.cmu.edu/afs/cs/user/ralf/pub/books/UndocumentedDOS/errata.ud2]}}{{usurped|1=[https://web.archive.org/web/20190417212906/https://www.pcjs.org/pubs/pc/programming/Undocumented_DOS/#errata-2nd-edition]}} (NB. On general methodology of reverse engineering, applied to mass-market software: a program for exploring DOS, disassembling DOS.)
* {{Cite book |title=Undocumented Windows: A Programmer's Guide to Reserved Microsoft Windows API Functions |last1=Schulman |first1=Andrew |display-authors=et al. |year=1992 |publisher=[[Addison Wesley]] |isbn=978-0-201-60834-2 |url-access=registration |url=https://archive.org/details/undocumentedwind00schu}} (pp.&nbsp;59–188 on general methodology of reverse engineering, applied to mass-market software: examining Windows executables, disassembling Windows, tools for exploring Windows)
* Schulman, Andrew, "Hiding in Plain Sight: Using Reverse Engineering to Uncover Software Patent Infringement," ''Intellectual Property Today'', Nov. 2010. Online: http://www.iptoday.com/issues/2010/11/hiding-in-plain-sight-using-reverse-engineering-to-uncover-software-patent-infringement.asp
* Schulman, Andrew, "Open to Inspection: Using Reverse Engineering to Uncover Software Prior Art," ''New Matter'' (Calif. State Bar IP Section), Summer 2011 (Part 1); Fall 2011 (Part 2). Online: http://www.SoftwareLitigationConsulting.com
*{{cite web |url=https://ewh.ieee.org/r5/denver/sscs/References/2007_09_Torrance.pdf |author=Thumm, Mike |title=Talking Tactics |access-date=2009-02-03 |work=IEEE 2007 Custom Integrated Circuits Conference (CICC) |publisher=IEEE, Inc |year=2007}}
{{div col end}}

{{Engineering fields}}
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[[Category:Reverse engineering| ]]
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