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722
bio website ethanheilman.tumblr.com
location Cambridge, MA
age 31
visits member for 3 years
seen Apr 18 at 0:02

Jul
19
comment Is it possible to derive the encryption method from encrypted text?
I disagree. What about all the detail one can deduce from block sizes, encryption modes, relative key size to block size, padding method, ciphertext length, non-random plaintext, key reuse (a problem for OTPs), related keys, fixed points.
Jul
19
answered Is it possible to derive the encryption method from encrypted text?
Jul
19
awarded  Organizer
Jul
19
revised Are there asymmetric cryptographic algorithms that are not based on integer factorization and discrete logarithm?
edited tags
Jul
18
answered Tactics available to help prove security of a new system?
Jul
18
awarded  Teacher
Jul
18
revised Is it possible to create an asymmetric cryptosystem where the private keys are not easily verifiable as such?
added 101 characters in body
Jul
18
awarded  Editor
Jul
18
revised Is it possible to create an asymmetric cryptosystem where the private keys are not easily verifiable as such?
added 1473 characters in body
Jul
18
answered Is it possible to create an asymmetric cryptosystem where the private keys are not easily verifiable as such?
Jul
15
comment What is the general justification for the hardness of finding preimages for cryptographic hash functions?
@Paulo Ebermann - Consider a less efficient function LP, that is essentially a mapping of all $2^n$ possible outputs to inputs. Such a function can find preimages in O(1) time, but requires 2^n space. Now compress this mapping into less than 2^n. Thus, for every hash function H there must exist an inverter function that finds preimages cheaper than brute force. All hash functions are "broken" the trick is discovering the function that breaks the hash function. If such a preimage finding function is too big, discovering it by brute force is hard.
Jul
15
comment What is the general justification for the hardness of finding preimages for cryptographic hash functions?
@Paulo Ebermann - For most hash functions there is no claim that such an efficient preimage finding function (or collision finding function) can't exist, but rather that the cryptography has not discovered (hence contests like SHA3). My question is what makes finding such a function hard?
Jul
15
comment What is the general justification for the hardness of finding preimages for cryptographic hash functions?
@Paulo Ebermann - The minimum number of bits that is required to describe a function. For example machine code can be used to describe a particular mapping from one set of integers to another. Given a hash function H, that is encoded using language L, can you find another function P such that P inverts H in the same time/memory complexity as H and that P encoded in L is smaller than the output size of H (the encoded description of P is smaller than the output size of H).
Jul
15
comment What is the general justification for the hardness of finding preimages for cryptographic hash functions?
@Paulo Ebermann - I mean that if an efficient preimage finding function is smaller in number of bits than the output size of the hash function then one could guess the preimage finding function faster than one could guess the preimage thereby breaking the hash function. By efficient, I mean a that the preimage function finds the preimage in roughly the same time as the hash function generates an output (that is the preimage function is an inversion of the hash function and not just a program that guesses at preimages).
Jul
13
awarded  Critic
Jul
13
awarded  Citizen Patrol
Jul
13
comment What is the general justification for the hardness of finding preimages for cryptographic hash functions?
What are the philosophical underpinnings of 'fuzzy' or 'cowboy' cryptography that attempt to explain why it is hard to break. While there is probably no known hard-science theory that explains why SHA2 hasn't been broken yet, there may be explanations in philosophy or other softer fields. What are the stories cryptographers tell themselves about why SHA2 provides resistance to attempts to break it?
Jul
12
comment What is the general justification for the hardness of finding preimages for cryptographic hash functions?
I know that there are functions that are justifiably hard to invert given a under a particular a mathematical assumption (discrete log problem as done in the paper provided). Most cryptographic hash functions do not use such assumptions, yet in practice they appear to be hard to invert. What is the thinking on why this is? Is the conventional wisdom that some mysterious one way property is hiding in xor-rotations and GF s-boxes?
Jul
12
awarded  Student
Jul
12
awarded  Supporter