Ethan Heilman

959 reputation

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bio	website	ethanheilman.tumblr.com
	location	Cambridge, MA
	age	30
visits	member for	1 year, 10 months
	seen	Apr 22 at 21:43
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Security Hobbyist

Github: Ethan Heilman
Twitter: Ethan Heilman

Play FlipIt:

http://ethanheilman.github.com/flipIt/playable_with_instructions.html

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	959 reputation	bio	website	ethanheilman.tumblr.com	visits	member for	1 year, 10 months
416 badges		location	Cambridge, MA		seen	Apr 22 at 21:43

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Nov 22	comment	Could one construct a cipher that is secure for friendly parties to use but insecure for hostile parties? @user11342 Where did your answer get moved? I can't seem to find it.
Nov 2	comment	How to deduce enigma settings given a partial plaintext? Yeah, my bad, I redid my calculations and ended up with the same answer as you.
Oct 28	comment	How to deduce enigma settings given a partial plaintext? Nice try, time traveling Alan Turing.
Oct 12	comment	Why has the RSA factoring challenge been withdrawn? Thanks Thomas! Someone should turn this into a question.
Oct 12	comment	Why has the RSA factoring challenge been withdrawn? According the wikipedia page: "[TWIRL'S designers] estimate that if TWIRL were built, it would be able to factor 1024-bit numbers in one year at the cost of 'a few dozen million US dollars'". Is this statement incorrect? Has something new been learned?
Oct 12	comment	Why has the RSA factoring challenge been withdrawn? What about research on custom cryptanalysis hardware such as TWIRL en.wikipedia.org/wiki/TWIRL
Sep 30	comment	What is the “Random Oracle Model” and why is it controversial? +1 for "There is a black box. In the box lives a gnome, with a big book and some dice."
Sep 28	comment	Is there a secure cryptosystem that can be performed mentally? OTP's can be done mentally, would you consider OTPs a fair answer?
Sep 28	comment	Time Capsule cryptography? @IlmariKaronen - Thanks, updated the link. I agree completely, an attacker could run a sequencing side-channel attack against the message. I said the same thing here: the-scientist.com/2011/09/26/encrypting-e-coli . Most security systems are built around models of what an attacker can do. For example AES can be broken by a timing side-channel, but that doesn't mean AES is no longer secure. Furthermore there are some pretty powerful countermeasures that could be used prevent to a sequencing side-channel attack.
Sep 27	comment	Would the ability to efficiently find Discrete Logs have any impact on the security of RSA? Can you find a citation that states that it is an open question if a break in DH would have implications for RSA?
Sep 27	comment	Preventing message replay with RSA @ChrisSmith Good point! We have three options: (1) as you pointed out storing the previous nonces works, (2). the first time a connection happens the nonce is generated and sent, each subsequent connection the nonce is incremented by 1 (since the attacker doesn't know the value of the nonce the attacker can't predict the new value of the nonce). (3). nonces passed between both parties and combined to generate new nonces (similar to the way syn cookies work en.wikipedia.org/wiki/…).
Sep 27	comment	Preventing message replay with RSA Why would including the expiration time in the message be insecure?
Sep 27	comment	Is Diffie-Hellman mathematically the same as RSA? I think I might be wrong, but I thought I've heard the claim that breaking discrete log breaks/threatens RSA as well. Maybe this should be a question.
Sep 26	comment	What is the best method to determine the language used in a monoalphabetic substitution cipher? @128 - absence of whitespace is typical, most classical ciphers assume you remove whitespace. Solving classical ciphers can get a bit tricky, if you are really interested I'd recommend: 'Cryptanalysis: a study of ciphers and their solution' ( books.google.com/books/about/Cryptanalysis.html?id=fKNB-7y_Hs4C ). Also 'The American Black Chamber' (amazon.com/American-Black-Chamber-Cryptographic/dp/0894121545) has a bit of advice, examples on solving classical ciphers.
Sep 26	comment	What is the best method to determine the language used in a monoalphabetic substitution cipher? Certainly you can use a monogram frequency chart to guess the language. Another idea would be to use a common word such as in german 'ein' and look for three letters that have the same distance from each other (assuming it is a shift cipher). Where did you get a ciphertext in which you know so little about it, yet you know that it is monoalphabetic?
Sep 24	comment	Is there a simple hash function that one can compute without a computer? @FUZxxl - I think it might be safe enough for class. Not sure how safe it is generally. It would make an interesting crypto question.
Sep 24	comment	Is there a simple hash function that one can compute without a computer? Yes, RO schemes typically require a trusted third party to keep the table of inputs and outputs and to generate new outputs.
Sep 24	comment	Is there a simple hash function that one can compute without a computer? What about a function, $f$, that given a number $n$, indexes e with $n \times 4$ and returns the next 4 digits of e. $$f(n) = e[n4],e[n4+1],e[n4+2],e[n4+3]$$ So $f(0)$ would return $2718$, f(1) would return $2818$ and so on. Or use a normal number instead of e ( en.wikipedia.org/wiki/Normal_number) is you want to be more formal.
Sep 23	comment	Is the following statement about PRG true or false? What about using bar $\|$ for concatenation? Is $.$ commonly used?
Sep 22	comment	Designing a key expander out of ciphers @DavidSchwartz - I've posted a complete version of my answer.