David Wachtfogel

2,911 reputation

119

bio	website	goodenoughsecurity.blogspot.c…
	location	Jerusalem, Israel
	age	39
visits	member for	9 months
	seen	Mar 13 at 7:51
stats	profile views	47

Digital security professional and manager. Work on chip hardware security (smart cards, USB tokens, consumer electronics), DRM, proprietary cryptography and protocols, embedded software security, end-to-end system security and security policy.

IT security (especially password security) is a hobby.

	2,911 reputation	bio	website	goodenoughsecurity.blogspot.c…	visits	member for	9 months
119 badges		location	Jerusalem, Israel		seen	Mar 13 at 7:51

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Nov 23	comment	anomaly detection: feature calculation problem @makerofthings7 In this case Google - but it's generally a good site for finding papers
Nov 21	comment	anomaly detection: feature calculation problem Try here: hal.archives-ouvertes.fr/docs/00/73/62/78/PDF/…
Nov 21	comment	Reset password - should I prevent abusing it? Security questions are a very weak form of user identification and shouldn't be used in lieu of a password - i.e. you should never grant access to a resource based only on a security question. But security questions are probably good enough to prevent false password resetting (which isn't much of a hack - it's just a nuisance) and you can't do much better than them for this purpose. CAPTCHAs aren't very good for this purpose since the attack can be done manually (you only need to do it once an hour to be very annoying).
Nov 7	comment	Encryption in an embeddded system If you assume that the attacker cannot modify the firmware then all you need to do is sign the file using RSA with PKCS#1 padding (which is good enough for your needs). sourceforge.net/projects/tplockbox has Delphi code for this; OpenSSL has C code. Since the information in the file (prices) is not secret there's no reason to encrypt the file.
Nov 5	comment	Potential consequences of using “Everyone” to manage permissions? This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post.
Nov 4	comment	Should Stack Exchange be more obscure in its systems' structure? As @RoryMcCune wrote in his response to security.stackexchange.com/questions/2430/…, obscurity shouldn't be relied on for security but there are situations where obscurity is good as an extra layer on an otherwise properly secured system. Obscurity isn't bad in itself - it's bad only if it is used to hide the fact that the system is otherwise not secure.
Nov 4	comment	What is SHA-3 and why did we change it? @PaŭloEbermann Sure.
Oct 31	comment	How can I encrypt a file with .NET and have the same file size of the original file? @Thomas - is this clearer now?
Oct 31	comment	How can I encrypt a file with .NET and have the same file size of the original file? @Thomas - which is why I wrote the two conditions above. I'll edit the post to clarify this point.
Oct 30	comment	How does syskey in Windows increase the security in a domain? You can +1 the answers :)
Oct 30	comment	How does syskey in Windows increase the security in a domain? As long as syskey is not stored on the Windows machine but in a removable storage device you should be OK. Graham Hill wrote in his response that if you map a USB drive to A:\ syskey will be written to that drive. If so that's probably you're best bet.
Oct 25	comment	How to suspend a user from my website and prevent them from creating a second account? See security.stackexchange.com/questions/19251/…
Oct 22	comment	Can someone detect the URL an android app uses? @CodesInChaos Good comment - made a small edit to clarify this point
Oct 16	comment	Do Client Nonces enhance the security of HTTP Digest Auth? Correct, but this would require the attacker to redo the exhaustive search for each password the attacker wants to crack. If it wasn't for the client nonce the attacker could do the exhaustive search operation once per username and build a hash table which could be used to attack the same username on many servers.
Oct 15	comment	Doing a dictionary attack on RSA if you have the public key? Take a look at Thomas Pornin's response at stackoverflow.com/a/7568183/1616145
Oct 15	comment	Base64 encode diffences in BCrypt implemenations Don't you mean "as long as $c2 is an 8-bit value"?
Oct 14	comment	Known password length, brute force character in place? @OlegV.Volkov That quote is taken out of context. Their analysis was done on a customer application but is based on simulated real world applications. I know for a fact that this attack is possible in the real world because I've actually done it on a test system.
Oct 14	comment	Known password length, brute force character in place? @OlegV.Volkov please read rdist.root.org/2010/07/19/exploiting-remote-timing-attacks - this exact attack was done by them. The paper talks about 20 microseconds - not milliseconds.
Oct 13	comment	Known password length, brute force character in place? @OlegV.Volkov Besides Nate Lawson's work I linked to in my previous comment, there's also this paper, cs.rice.edu/~dwallach/pub/crosby-timing2009.pdf, which states that time differences as small as 20 microseconds can be detected over the Internet.
Oct 13	comment	Known password length, brute force character in place? That's why I wrote you would need to try each multiple times - to cancel out the noise. This has been done succesfully by many reseachers - for example, please see rdist.root.org/2010/07/19/exploiting-remote-timing-attacks.