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The document discusses software and hardware security. It describes the Digital Security group at Radboud University which uses rigorous and formal methods to design and analyze secure ICT systems, considering their societal impact especially on privacy. The group also looks at concrete applications of their research in areas like software security, hardware security, online privacy, and cybercrime.

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Software & Hardware Security Erik Poll Digital Security group Radboud University Nijmegen The Netherlands
Nijmegen 2
Digital Security group Rigorous & formal methods to design & analyse secure ICT systems Incl. societal impact, esp. on privacy Also looking at concrete applications
software security hardware security attacks • buffer overflows in C(++) • web problems: SQL inj, XSS, CSRF,.. defenses • security testing • static analysis for Java & C • smartcards & RFID • attacks • bank cards • e-passport 4 online privacy & cybercrime
The problem
pre-history of hacking In 1950s, Joe Engressia showed the telephone network could be hacked by phone phreaking: ie. whistling at right frequencies http://www.youtube.com/watch?v=vVZm7I1CTBs In 1970s, before founding Apple together with Steve Jobs, Steve Wozniak sold Blue Boxes for phone phreaking at university sw s1 6
Slammer Worm (2003) Pictures taken from The Spread of the Sapphire/Slammer Worm, by David Moore, Vern Paxson, Stefan Savage, Colleen Shannon, Stuart Staniford, Nicholas Weaver 7
Slammer Worm (2003) Pictures taken from The Spread of the Sapphire/Slammer Worm, by David Moore, Vern Paxson, Stefan Savage, Colleen Shannon, Stuart Staniford, Nicholas Weaver 8
9
Top secret NSA slides leaked by Edward Snowden More info at http:// leaksource.info and http:// www.theguardian.com/us-news/the-nsa-files 10
11
12
Security problems of past days… To get an impression of the scale of the problem, have a look at http://www.securityfocus.com/vulnerabilities http://www.us-cert.gov/ncas/alerts http://www.us-cert.gov/ncas/bulletins http://www.securitytracker.com/ 13
Quiz What do laptops, tablets, mobile phones, wifi access points, network routers, bank cards, e-passports, eID cards, smartphone apps, web sites, web browsers, web servers, operating systems, firewalls, intrusion detection systems, cars, and airplanes have in common? Why can all these things be hacked, if we are not very careful? There is SOFTWARE inside them! 14
Software (in)security • Software is the main source of security problems. – Software is the weakest link in the security chain, with the possible exception of “the human factor” • Software security does (did?) not get much attention – in other security courses, or – in programming courses, or indeed, in much of the security literature! Computer security courses traditionally focus on cryptography…f be solve by cryptography, you do not understand cryptography and you do not understand your problem” [Bruce Schneier] 15
“if you think your problem can be solved by cryptography, then you do not understand cryptography and you do not understand your problem” [Bruce Schneier] 16
Superficial analysis of the problem 17
Observation 1 All these problems are due to (bad) software Namely software in • the Linux/Windows/Mac operating system (OS) • web servers • web browsers • the router software • ... Because of these software bugs constant patching of system is needed to keep them secure 18
Observation 2 All these problems are due to bad software that • can be executed/addressed over the network – eg. in case of Slammer worm • executes on (untrusted) input obtained over the network or both With ever more network connectivity, ever more software can be attacked. 19
Changing target of attacks • Traditionally, focus of attacks was on operating system and network “Solutions” – regular patching of OS – firewalls – virus scanners • Increasingly, focus on • web applications • web browser • mobile devices • smartphones, tablet, that pass through firewalls • embedded software • software in cars, factories, infrastructure... and targetted attacks on specific organisation or person (known as ATP = Advanced Persistent Threat) 20
Changing nature of attackers Traditionally, hackers were amateurs motivated by fun • publishing attacks for fame & glory • attacks creating lots of publicity Increasingly, hackers are professional • attackers go underground • zero-day exploits are worth a lot of money Attackers increasingly include • organized crime with lots of money and (hired) expertise • government agencies: with even more money & in-house expertise 21
stuxnet attack Malware (by US and Israel?) attacking nuclear enrichment facility in Iran http://www.ted.com/talks/ralph_langner_cracking_stuxnet_a_21st_century_cyberweapon.html 22
Software (in)security: crucial facts • No silver bullets! crypto or special security features do not magically solve all problems • Security is emergent property of entire system – just like quality • (Non-functional) security aspects should be integral part of the design, right from the start 23
We focus on software security now, but don’t forget that security is about people (users, employees, sys-admins, programmers,...), and their laziness, mistakes, stupidity, incompetence, confusion, software, bugs, verification, hackers, viruses, testing, operating systems, networks, databases, hardware, access control, passwords, smartcards, biometrics, cryptology, security protocols, security policies & their enforcement, monitoring, auditing, risk management, complexity, legislation, persecution, liability, public relations public perception, conventions, standards, ….. 24
The causes of the problem 25
Quick audience poll • How many of you learned to program in C or C++? • How many had it as a first programming language? • How many of your C(++) courses • warned you about buffer overflows? • explained how to avoid them? Major causes of problems are • lack of awareness • lack of knowledge • irresponsible teaching of dangerous programming languages 26
Quick audience poll • How many of you have built a web-application? – in which programming languages? • What is the secure way of doing a SQL query in this language? (to avoid SQL injection flaws) Major causes of problems are • lack of awareness • lack of knowledge 27
1. Security is always a secondary concern • Security is always a secondary concern – primary goal of software is to provide some functionality or services; – managing associated risks is a derived/secondary concern • There is often a trade-off/conflict between – security – functionality & convenience where security typically looses out • more examples of this later... 28
29
Functionality vs security • Functionality is about what software should do, security is (also) about what it should not do Unless you think like an attacker, you will be unaware of any potential threats 30
Functionality vs security: Lost battles? • operating systems (OSs) – with huge OS, with huge attack surface • programming languages – with easy to use, efficient, but very insecure and error-prone mechanisms • web browsers – with plug-ins for various formats, javascript, ActiveX, Ajax ... • email clients – which automatically cope with all sorts of formats & attachments.. 31
Functionality vs security : PHP "After writing PHP forum software for three years now, I've come to the conclusion that it is basically impossible for normal programmers to write secure PHP code. It takes far too much effort. .... PHP's raison d'etre is that it is simple to pick up and make it do something useful. There needs to be a major push ... to make it safe for the likely level of programmers - newbies. Newbies have zero chance of writing secure software unless their language is safe. ... " [Source http://www.greebo.cnet/?p=320] 32
2. Weakness in depth programming languages hardware (incl network card & peripherals) application operating system webbrowser with plugins platform eg Java or .NET system APIs middleware libraries interpretable or executable input eg paths, filenames, .doc, .xls, .pdf, .js,... sql data base 33
2. Weakness in depth Software • runs on a huge, complicated infrastructure – OS, platforms, webbrowser, lots of libraries & APIs, ... • is built using complicated languages & formats – programming languages, but also SQL, HTML, XML, ... • using various tools – compilers, IDEs, preprocessors, dynamic code downloads These may have security holes, or may make the introduction of security holes very easy & likely 34
Recap Problems are due to • lack of awareness – of threats, but also of what should be protected • lack of knowledge – of potential security problems, but also of solutions • compounded by complexity – software written in complicated languages, using large APIs , and running on huge infrastructure • people choosing functionality over security 35
Security concepts & goals
Security • Security is about regulating access to assets – assets can be information, functionality, or physical assets – • Software provides functionality – eg on-line exam results • This functionality comes with certain risks – eg what are risks of on-line exam results? • (Software) security is about managing these risks 37
Starting point for ensuring security • Any discussion of security should start with an inventory of – the stakeholders – ie. who is involved – their assets, and – the threats to these assets by possible attackers – employees, clients, script kiddies, criminals Any discussion of security without understanding these issues is meaningless: You have to know what you want to secure, against what type of attacks, and against who 38
Security concepts Goal of security is to reduce risks to acceptable levels, • Security is never 100% So you have to know what you want to secure, against what type of attacks, against who, and at what cost 39
Security Objectives: CIA • Confidentiality – unauthorised users cannot read information • Integrity – unauthorised users cannot alter information • Availability – authorised users can access information – ie. preventing DoS (Denial of Service) attacks • Non-repudiation or accountability – authorised users cannot deny actions 40
Security objectives • Integrity nearly always more important than confidentiality Eg think of – your bank account information – your medical records – all the software you use, incl. the entire OS 41
How to realise security objectives? AAAA • Authentication – who are you? • Access control/Authorisation – control who is allowed to do what – this requires a specification of who is allowed to do what • Auditing – check if anything went wrong • Action – if so, take action 42
How to realise security objectives? Other names for the last three A's • Prevention – measures to stop breaches of security goals • Detection – measures to detect breaches of security goals • Reaction – measures to recover assets, repair damage, and persecute (and deter) offenders 43
Try to prevent, but also detect and react Never think that good prevention makes detection & reaction superfluous. Eg. breaking into house or office is often easy; only detection & reaction seriously deters burglars. Detection of digital break-in is harder who noticed a break-in on his computer recently? Reaction (incl. prosecution) is even harder how to find the person responsible, somewhere on the internet?
Software security
warning: confusing terminology Common use of terminology can be very confused & confusing: (security) weakness, flaw, vulnerability, bug, error, coding defect... We can make a distinction between • a security weakness/flaw: something that is wrong or could be better • a security vulnerability a weakness/flaw that can actually be exploited by an attacker, which requires the flaw to be - accessible: attacker has to be able to get at it - exploitable: attacker has to be able to do some damage with it Eg by unplugging your network connection, some (many?) vulnerabilities become flaws. 46
software vulnerabilities Software vulnerabilities can be introduced at two “levels” • design flaws vulnerability in the design • bugs aka implementation flaws or code-level defects vulnerability in the software introduced when implementing a system Rough consensus: bugs and design flaws are equally common Vulnerabilities also arise on other levels (out of scope for now) • configuration flaw when installing software on a machine • the user • unforeseen consequence of the intended functionality (eg. spam) 47
Typical software security vulnerabilities Security bugs found in Microsoft bug fix month (2002) 37% 20% 26% 17% 0% buffer overflow input validation code defect design defect crypto 48
bugs aka implementation flaws aka code-level defects There are roughly two kinds of implementation flaws 1. bugs that can be understood looking at the program itself (and understanding what it is meant to do!) – eg. , simple typos, confusing two program variables, off-by-one error in array access, ... – sometimes called logic errors, as opposed to syntax errors, or an errors in the program logic 2. lower-level problems that can only be spotted if you understand the underlying platform of the program in execution, eg – buffer overflow,integer overflow,... in binaries compiled from C(++) – SQL injection, XSS, CSRF,.... in web-applications 49
The big problem of software security The bad news people keep making the same (types of) mistakes The good news people keep making the same (types of) mistakes …… so we can do something about it! “Every advantage has its disadvantage ” -- Johan Cruijff 50
security in the software development life cycle
Tackling Software Insecurity • Knowledge about standard mistakes is crucial in preventing them – these depends on the programming language, the “platform” (OS, database systems, web-application framework,…), and the type of application – lots of info available on this now • But this is not enough: security to be taken into account from the start, throughout software development life cycle – several ideas & methodologies to do this 52
Security in Software Development Life Cycle [Gary McGraw, Software security, Security & Privacy Magazine, IEEE, Vol 2, No. 2, pp. 80-83, 2004. ] McGraw’s Touchpoints 53
Methodologies for security in development life cycle Common/best practices, with methods for assessments, and roadmaps for improvement • McGraw’s Touchpoints BSIMM Building Security In – Maturity Model http://bsimm.com • Microsoft SDL Security Development Lifecycle • OpenSAMM Software Assurance Maturity Model http://opensamm.org 54
Microsoft’s SDL Optimisation Model 55
BSIMM Based on data collected from large enterprises 56
Spot the (security) flaws in electronic_purse.c int balance; void decrease(int amount) { if (balance <= amount) { balance = balance – amount; } else { printf(“Insufficient fundsn”); } } void increase(int amount) { balance = balance + amount; } <= should be >= what if this sum is too large for an int? what if amount is negative? 57
Different kinds of implementation flaws • lack of input validation of (untrusted) user input – could be a design flaw rather than an implementation flaw? – more “fundamental” than the flaws below • simple mistake in the program logic • potential problem depending on how the underlying platform work, eg. in case of an integer overflow; – “lower level” than the flaws above <= should be >= what if amount is negative? what if this sum is too large for an int? 58
More info • Gary McGraw, Software security, Security & Privacy Magazine, IEEE, Vol 2, No. 2, pp. 80-83, 2004. • Check out websites http://www.us-cert.gov/ncas/alerts/ http://www.us-cert.gov/ncas/bulletins/ http://www.securitytracker.com/ http://www.securityfocus.com/vulnerabilities for security alerts in the past week 59

More Related Content

1_Introduction.pdf

  • 1. Software & Hardware Security Erik Poll Digital Security group Radboud University Nijmegen The Netherlands
  • 3. Digital Security group Rigorous & formal methods to design & analyse secure ICT systems Incl. societal impact, esp. on privacy Also looking at concrete applications
  • 4. software security hardware security attacks • buffer overflows in C(++) • web problems: SQL inj, XSS, CSRF,.. defenses • security testing • static analysis for Java & C • smartcards & RFID • attacks • bank cards • e-passport 4 online privacy & cybercrime
  • 6. pre-history of hacking In 1950s, Joe Engressia showed the telephone network could be hacked by phone phreaking: ie. whistling at right frequencies http://www.youtube.com/watch?v=vVZm7I1CTBs In 1970s, before founding Apple together with Steve Jobs, Steve Wozniak sold Blue Boxes for phone phreaking at university sw s1 6
  • 7. Slammer Worm (2003) Pictures taken from The Spread of the Sapphire/Slammer Worm, by David Moore, Vern Paxson, Stefan Savage, Colleen Shannon, Stuart Staniford, Nicholas Weaver 7
  • 8. Slammer Worm (2003) Pictures taken from The Spread of the Sapphire/Slammer Worm, by David Moore, Vern Paxson, Stefan Savage, Colleen Shannon, Stuart Staniford, Nicholas Weaver 8
  • 9. 9
  • 10. Top secret NSA slides leaked by Edward Snowden More info at http:// leaksource.info and http:// www.theguardian.com/us-news/the-nsa-files 10
  • 11. 11
  • 12. 12
  • 13. Security problems of past days… To get an impression of the scale of the problem, have a look at http://www.securityfocus.com/vulnerabilities http://www.us-cert.gov/ncas/alerts http://www.us-cert.gov/ncas/bulletins http://www.securitytracker.com/ 13
  • 14. Quiz What do laptops, tablets, mobile phones, wifi access points, network routers, bank cards, e-passports, eID cards, smartphone apps, web sites, web browsers, web servers, operating systems, firewalls, intrusion detection systems, cars, and airplanes have in common? Why can all these things be hacked, if we are not very careful? There is SOFTWARE inside them! 14
  • 15. Software (in)security • Software is the main source of security problems. – Software is the weakest link in the security chain, with the possible exception of “the human factor” • Software security does (did?) not get much attention – in other security courses, or – in programming courses, or indeed, in much of the security literature! Computer security courses traditionally focus on cryptography…f be solve by cryptography, you do not understand cryptography and you do not understand your problem” [Bruce Schneier] 15
  • 16. “if you think your problem can be solved by cryptography, then you do not understand cryptography and you do not understand your problem” [Bruce Schneier] 16
  • 17. Superficial analysis of the problem 17
  • 18. Observation 1 All these problems are due to (bad) software Namely software in • the Linux/Windows/Mac operating system (OS) • web servers • web browsers • the router software • ... Because of these software bugs constant patching of system is needed to keep them secure 18
  • 19. Observation 2 All these problems are due to bad software that • can be executed/addressed over the network – eg. in case of Slammer worm • executes on (untrusted) input obtained over the network or both With ever more network connectivity, ever more software can be attacked. 19
  • 20. Changing target of attacks • Traditionally, focus of attacks was on operating system and network “Solutions” – regular patching of OS – firewalls – virus scanners • Increasingly, focus on • web applications • web browser • mobile devices • smartphones, tablet, that pass through firewalls • embedded software • software in cars, factories, infrastructure... and targetted attacks on specific organisation or person (known as ATP = Advanced Persistent Threat) 20
  • 21. Changing nature of attackers Traditionally, hackers were amateurs motivated by fun • publishing attacks for fame & glory • attacks creating lots of publicity Increasingly, hackers are professional • attackers go underground • zero-day exploits are worth a lot of money Attackers increasingly include • organized crime with lots of money and (hired) expertise • government agencies: with even more money & in-house expertise 21
  • 22. stuxnet attack Malware (by US and Israel?) attacking nuclear enrichment facility in Iran http://www.ted.com/talks/ralph_langner_cracking_stuxnet_a_21st_century_cyberweapon.html 22
  • 23. Software (in)security: crucial facts • No silver bullets! crypto or special security features do not magically solve all problems • Security is emergent property of entire system – just like quality • (Non-functional) security aspects should be integral part of the design, right from the start 23
  • 24. We focus on software security now, but don’t forget that security is about people (users, employees, sys-admins, programmers,...), and their laziness, mistakes, stupidity, incompetence, confusion, software, bugs, verification, hackers, viruses, testing, operating systems, networks, databases, hardware, access control, passwords, smartcards, biometrics, cryptology, security protocols, security policies & their enforcement, monitoring, auditing, risk management, complexity, legislation, persecution, liability, public relations public perception, conventions, standards, ….. 24
  • 25. The causes of the problem 25
  • 26. Quick audience poll • How many of you learned to program in C or C++? • How many had it as a first programming language? • How many of your C(++) courses • warned you about buffer overflows? • explained how to avoid them? Major causes of problems are • lack of awareness • lack of knowledge • irresponsible teaching of dangerous programming languages 26
  • 27. Quick audience poll • How many of you have built a web-application? – in which programming languages? • What is the secure way of doing a SQL query in this language? (to avoid SQL injection flaws) Major causes of problems are • lack of awareness • lack of knowledge 27
  • 28. 1. Security is always a secondary concern • Security is always a secondary concern – primary goal of software is to provide some functionality or services; – managing associated risks is a derived/secondary concern • There is often a trade-off/conflict between – security – functionality & convenience where security typically looses out • more examples of this later... 28
  • 29. 29
  • 30. Functionality vs security • Functionality is about what software should do, security is (also) about what it should not do Unless you think like an attacker, you will be unaware of any potential threats 30
  • 31. Functionality vs security: Lost battles? • operating systems (OSs) – with huge OS, with huge attack surface • programming languages – with easy to use, efficient, but very insecure and error-prone mechanisms • web browsers – with plug-ins for various formats, javascript, ActiveX, Ajax ... • email clients – which automatically cope with all sorts of formats & attachments.. 31
  • 32. Functionality vs security : PHP "After writing PHP forum software for three years now, I've come to the conclusion that it is basically impossible for normal programmers to write secure PHP code. It takes far too much effort. .... PHP's raison d'etre is that it is simple to pick up and make it do something useful. There needs to be a major push ... to make it safe for the likely level of programmers - newbies. Newbies have zero chance of writing secure software unless their language is safe. ... " [Source http://www.greebo.cnet/?p=320] 32
  • 33. 2. Weakness in depth programming languages hardware (incl network card & peripherals) application operating system webbrowser with plugins platform eg Java or .NET system APIs middleware libraries interpretable or executable input eg paths, filenames, .doc, .xls, .pdf, .js,... sql data base 33
  • 34. 2. Weakness in depth Software • runs on a huge, complicated infrastructure – OS, platforms, webbrowser, lots of libraries & APIs, ... • is built using complicated languages & formats – programming languages, but also SQL, HTML, XML, ... • using various tools – compilers, IDEs, preprocessors, dynamic code downloads These may have security holes, or may make the introduction of security holes very easy & likely 34
  • 35. Recap Problems are due to • lack of awareness – of threats, but also of what should be protected • lack of knowledge – of potential security problems, but also of solutions • compounded by complexity – software written in complicated languages, using large APIs , and running on huge infrastructure • people choosing functionality over security 35
  • 37. Security • Security is about regulating access to assets – assets can be information, functionality, or physical assets – • Software provides functionality – eg on-line exam results • This functionality comes with certain risks – eg what are risks of on-line exam results? • (Software) security is about managing these risks 37
  • 38. Starting point for ensuring security • Any discussion of security should start with an inventory of – the stakeholders – ie. who is involved – their assets, and – the threats to these assets by possible attackers – employees, clients, script kiddies, criminals Any discussion of security without understanding these issues is meaningless: You have to know what you want to secure, against what type of attacks, and against who 38
  • 39. Security concepts Goal of security is to reduce risks to acceptable levels, • Security is never 100% So you have to know what you want to secure, against what type of attacks, against who, and at what cost 39
  • 40. Security Objectives: CIA • Confidentiality – unauthorised users cannot read information • Integrity – unauthorised users cannot alter information • Availability – authorised users can access information – ie. preventing DoS (Denial of Service) attacks • Non-repudiation or accountability – authorised users cannot deny actions 40
  • 41. Security objectives • Integrity nearly always more important than confidentiality Eg think of – your bank account information – your medical records – all the software you use, incl. the entire OS 41
  • 42. How to realise security objectives? AAAA • Authentication – who are you? • Access control/Authorisation – control who is allowed to do what – this requires a specification of who is allowed to do what • Auditing – check if anything went wrong • Action – if so, take action 42
  • 43. How to realise security objectives? Other names for the last three A's • Prevention – measures to stop breaches of security goals • Detection – measures to detect breaches of security goals • Reaction – measures to recover assets, repair damage, and persecute (and deter) offenders 43
  • 44. Try to prevent, but also detect and react Never think that good prevention makes detection & reaction superfluous. Eg. breaking into house or office is often easy; only detection & reaction seriously deters burglars. Detection of digital break-in is harder who noticed a break-in on his computer recently? Reaction (incl. prosecution) is even harder how to find the person responsible, somewhere on the internet?
  • 46. warning: confusing terminology Common use of terminology can be very confused & confusing: (security) weakness, flaw, vulnerability, bug, error, coding defect... We can make a distinction between • a security weakness/flaw: something that is wrong or could be better • a security vulnerability a weakness/flaw that can actually be exploited by an attacker, which requires the flaw to be - accessible: attacker has to be able to get at it - exploitable: attacker has to be able to do some damage with it Eg by unplugging your network connection, some (many?) vulnerabilities become flaws. 46
  • 47. software vulnerabilities Software vulnerabilities can be introduced at two “levels” • design flaws vulnerability in the design • bugs aka implementation flaws or code-level defects vulnerability in the software introduced when implementing a system Rough consensus: bugs and design flaws are equally common Vulnerabilities also arise on other levels (out of scope for now) • configuration flaw when installing software on a machine • the user • unforeseen consequence of the intended functionality (eg. spam) 47
  • 48. Typical software security vulnerabilities Security bugs found in Microsoft bug fix month (2002) 37% 20% 26% 17% 0% buffer overflow input validation code defect design defect crypto 48
  • 49. bugs aka implementation flaws aka code-level defects There are roughly two kinds of implementation flaws 1. bugs that can be understood looking at the program itself (and understanding what it is meant to do!) – eg. , simple typos, confusing two program variables, off-by-one error in array access, ... – sometimes called logic errors, as opposed to syntax errors, or an errors in the program logic 2. lower-level problems that can only be spotted if you understand the underlying platform of the program in execution, eg – buffer overflow,integer overflow,... in binaries compiled from C(++) – SQL injection, XSS, CSRF,.... in web-applications 49
  • 50. The big problem of software security The bad news people keep making the same (types of) mistakes The good news people keep making the same (types of) mistakes …… so we can do something about it! “Every advantage has its disadvantage ” -- Johan Cruijff 50
  • 51. security in the software development life cycle
  • 52. Tackling Software Insecurity • Knowledge about standard mistakes is crucial in preventing them – these depends on the programming language, the “platform” (OS, database systems, web-application framework,…), and the type of application – lots of info available on this now • But this is not enough: security to be taken into account from the start, throughout software development life cycle – several ideas & methodologies to do this 52
  • 53. Security in Software Development Life Cycle [Gary McGraw, Software security, Security & Privacy Magazine, IEEE, Vol 2, No. 2, pp. 80-83, 2004. ] McGraw’s Touchpoints 53
  • 54. Methodologies for security in development life cycle Common/best practices, with methods for assessments, and roadmaps for improvement • McGraw’s Touchpoints BSIMM Building Security In – Maturity Model http://bsimm.com • Microsoft SDL Security Development Lifecycle • OpenSAMM Software Assurance Maturity Model http://opensamm.org 54
  • 56. BSIMM Based on data collected from large enterprises 56
  • 57. Spot the (security) flaws in electronic_purse.c int balance; void decrease(int amount) { if (balance <= amount) { balance = balance – amount; } else { printf(“Insufficient fundsn”); } } void increase(int amount) { balance = balance + amount; } <= should be >= what if this sum is too large for an int? what if amount is negative? 57
  • 58. Different kinds of implementation flaws • lack of input validation of (untrusted) user input – could be a design flaw rather than an implementation flaw? – more “fundamental” than the flaws below • simple mistake in the program logic • potential problem depending on how the underlying platform work, eg. in case of an integer overflow; – “lower level” than the flaws above <= should be >= what if amount is negative? what if this sum is too large for an int? 58
  • 59. More info • Gary McGraw, Software security, Security & Privacy Magazine, IEEE, Vol 2, No. 2, pp. 80-83, 2004. • Check out websites http://www.us-cert.gov/ncas/alerts/ http://www.us-cert.gov/ncas/bulletins/ http://www.securitytracker.com/ http://www.securityfocus.com/vulnerabilities for security alerts in the past week 59