74 reputation
4
bio website wallutis.de
location Germany
age 49
visits member for 1 year, 8 months
seen Dec 29 '12 at 22:10

Im working as an IT Consultant (mainly Microsoft Exchange). Interested in mathematics, IT security and cryptography.


Dec
28
awarded  Teacher
Dec
27
awarded  Supporter
Dec
27
answered What exactly is a negligible (and non-negligible) function?
Dec
23
comment Looking for examples for “proof by reduction”
The only problem: this solution looks too easy...
Dec
23
comment Looking for examples for “proof by reduction”
Sorry for the delay; end-of-year stress;-) Here is my answer (so far i have no response; so i dont know if it is correct): Lets assume that A' is not collision-resistent. We write H'=H(y) instead of H'=H(H(x)). Then "collision-resistant" means: there exists y,y' with H(y)=H(y'), y<>y' When we now look at A, then H: {0,1}* -> {0,1}^l (arbitrary length -> fixed-length l) H': {0,1}^l -> {0,1}^l (fixed-length -> fixed-length) If H' is not collision-resistant, then we have y,y' with H(y)=H(y'). That is a special case of H and that would mean that H is not collision-resistant too.
Nov
25
comment Looking for examples for “proof by reduction”
@Ricky: You are (formally) right. I have no idea how to add an upper s to H;-) But it is correct: in the line with H'(x)=H(H(x)) there are upper s missing on H. In "Katz/Lindell: Introduction to modern cryptography (Page 129)" (Gen, H) is called a Hash function in the definition; but its mentioned in the text that it is a familiy of Hash functions and s picks one function.
Nov
25
asked Looking for examples for “proof by reduction”
Nov
25
comment Pseudorandom generator and AE-secure encryption
not really homework. These is from a list of exam question that i need to understand. Its one question on a list of 6 multiple choice question. In the exam it wasnt necessary to give an explanation, but i want to understand it.
Nov
24
comment Pseudorandom generator and AE-secure encryption
I try to translate the definition of AE-secure that is in my lecture notes: An encryption scheme is AE-secure, if it is secure against Chosen-cyphertext attacks and provides authenticity.
Nov
24
awarded  Autobiographer
Nov
24
awarded  Student
Nov
24
asked Pseudorandom generator and AE-secure encryption