Polynomial

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Pentester, ex-developer, security researcher, reverse engineer, electronics tinkerer, internet activist, zombie eradicator, promulgator of useless facts, shrubbery inspector, bacon aficionado.

Strengths: Security, Crypto, Win32 API, C#, .NET, PHP, x86 assembly

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Opinions are my own. Advice provided with no warranty.

	479 reputation	bio	website	en.wikipedia.org/wiki/…	visits	member for	1 year, 6 months
113 badges		location	United Kingdom		seen	May 17 at 9:04

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Nov 23	comment	Security of simple xor and s-box cipher? For every single block there are 16 rounds, i.e. $C_n = M_n$, then loop $C_n = S[K_r \oplus C_n]$ for $r = 0 \to 15$ for each block $n$.
Nov 23	comment	Security of simple xor and s-box cipher? @EthanHeilman - Done.
Nov 23	revised	Security of simple xor and s-box cipher? re-added the original scheme
Nov 23	comment	Security of simple xor and s-box cipher? Sorry, must've missed it off my re-write. If you take a look at the edit history, you'll see my original design. It specifies 16 rounds of $C_n = S[K_r \oplus M_n]$ on each block. Would this result in any significant changes in the feasibility of the attacks you described?
Nov 23	awarded	Commentator
Nov 23	comment	Security of simple xor and s-box cipher? Does the known plaintext not get prevented by the use of multiple rounds? Since it's essentially $C_n = S[S[S[K_n \oplus M_n] \oplus M_{n+1}] \oplus M_{n+2} ... ]]]$
Nov 23	comment	Desirable S-box properties It doesn't really explain why they made the choices they did, though. It just says "this is the S-box and these are the choices we made". I'm really looking for answers that provide both an explanation of the facts and the reasoning behind making the choices.
Nov 23	comment	Desirable S-box properties The output of the cipher has the avalanche property and appears random, but the construction of the S-box is not random. It's a case of not allowing any correlation, rather than specifying that a particular output is not allowed.
Nov 23	comment	Security of simple xor and s-box cipher? Just a note to anyone reading this and being confused (e.g. with poncho's mentioning of "Step 2"), there was a cleanup and the question was changed. You can view the original question in the edit history.
Nov 23	comment	Is a RSA-signature of some identifying data a safe way to implement a license key? Windows product IDs are NOT unique. Mass user OEM licenses have the same key for every machine. I'd suggest fetching the motherboard and C drive serial numbers instead (you can do this with WMI).
Nov 23	comment	Desirable S-box properties My rational is that `S[a] = a` provides no benefit and `S[a] = !a` will always maintain the same bit "pattern" as its input. Since the idea of an S-box is to provide "confusion" (as defined by Shannon), it seems reasonable to ensure that neither of these cases are allowed. I may, however, be incorrect.
Nov 23	awarded	Supporter
Nov 23	awarded	Editor
Nov 23	comment	Security of simple xor and s-box cipher? @poncho - Yes, that's correct.
Nov 23	revised	Security of simple xor and s-box cipher? re-wrote to be more general
Nov 23	comment	How can we reason about the cryptographic capabilities of code-breaking agencies like the NSA or GCHQ? They can always resort to the "Jack Bauer Side-Channel Attack", which involves them drilling holes in your kneecaps until you reveal the key. Billion dollar supercomputer or one agent with a $50 hammer drill... hey, I guess you can put a price on human rights!
Nov 23	awarded	Student
Nov 23	comment	Security of simple xor and s-box cipher? "In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation" - I'd say that my cipher fits that definition. Regardless, it's semantics, and its name doesn't affect its security (or lack thereof). I'm really just trying to learn here.
Nov 23	asked	Desirable S-box properties
Nov 23	comment	Security of simple xor and s-box cipher? Yes, there is an inverse S-box. I don't see why there should be an issue with having CBC tied into my cipher design as long as I'm designing it only for CBC.