Tag Info

New answers tagged

3

I believe Thomas Pornin's answer is by far superior to mine, but perhaps this answer can provide a simplification to his answer. When you initially hash some data, the possible input is infinite/limitless. You could input "abcdefghi...", "123456...", etcetera. However, the resulting hash possibilities are finite/limited. One of the beautiful things about ...


22

If you repeatedly apply a generic function on its result, in a finite domain, you tend to obtain a "rho" structure: at some point, you enter a cycle whose length is (roughly) $\sqrt{N}$, where $N$ is the size of the output space for your function. In the case of MD5, $N = 2^{128}$ (MD5 outputs 128-bit values), so the cycle will have length about $2^{64}$ ...


3

Probably yes, the shortage of human-generated entropy seems to have caused real problems: in this declassified memo (starting last paragraph of page 1), written for the 50 years of the VENONA project, is a documented case where OTP duplication is what enabled cryptanalysis; at least allegedly (from where we stand it is hard to tell if this whole story is ...


7

In World War II, this practice of generating "random" code books by hand is known to have been used by the Special Operations Executive, or SOE: Various techniques have been used to do the random generation. Marks describes how SOE agents’ silken keys were manufactured in Oxford by little old ladies shuffling counters. (Security Engineering: A ...


0

Combining 3 sources A,B and C is not obvious. The right thing to do is not A+B+C. It is A*B+C within a field (E.G. a GF(2^8) field, which maps to bytes). This is based on a 2006 paper by Barack Impagliazzo and Wigdersen (http://dl.acm.org/citation.cfm?id=1328011) that shows that this is a good extractor. You still need to post extract the output with an ...


0

The Von Neumann whitener would not meet your needs, nor would the more modern Yuval Peres whitener (which is an iterated Von Neumann algorithm). This is because the input requirements for the algorithm are that the bits be statistically independent. No raw noise source provides statistically independent bits. Your only choice is to use an extractor that is ...


0

Are M and C correlated? No. The distribution that the values the M and C may take on are independent of each other. The condition probability distribution that M has is unchanged no matter what the observed C value is. This is true whether you are using the statistical meaning of correlation, or whether you are looking more specifically at linear ...


1

When NIST put together the table A.1, they accidentally used a 96 character alphabet for that last column, not a 94 character one. One way to see this is looking at the bottom most entry; they list that $log_2(b^{40}) \approx 263.4$, where $b$ is the alphabet size they used. If we solve for $b$, we get $b \approx 96.002...$.


1

Low entropy for PRNGs is bad. If you set up a VM by automatized software, you won't have entropy for your PRNG which is not good. What would be the risk level? Weak cryptographic keys (pretty bad if this is f.ex. a SSH log-in key or someting like this). Seeding the VM with entropy rich data from the host is the standard solution and will solve the problem. ...



Top 50 recent answers are included