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 Yearling
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Jan
27
comment Plaintext attacks: affine cipher
@kodlu There is no $c_1$ in that part of the question (the part where $p$ is unknown).
Jan
22
answered Is $\mathbb R^3 $ subspace of $\mathbb R^4 $
Jan
12
comment Negation of injectivity
There is no "but" in logic, the negation of "P implies Q" is "P and not Q".
Dec
31
awarded  Yearling
Dec
4
comment Why is this prime a bad choice for the ElGamal cryptosystem?
Ask your favourite search engine about the Pohlig-Hellman algorithm.
Dec
2
comment Quotient ring $\mathbb{Z}/4\mathbb{Z}$
One thing to remember when working with quotient groups (rings, etc.) is that an element of the quotient structure is a subset of the original structure. Hence one immediately sees that your definition of Z/4Z is off because you define its elements to be integers, when they actually are sets of integers.
Dec
1
comment Reference Request for Topics in Group Theory
A specialised group theory textbook (as opposed to a general algebra one) will obviously cover it in more depth. I like the book of Roman, but there are many others.
Nov
29
comment Uses of vector spaces over $\mathbb Q$
Basically all of classical algebraic number theory, for starters, which was developed to answer questions about the good ol' integers.
Nov
22
comment Is there a surjective homomorphism from $Z$ to $\mathbb{Z}_2\times \mathbb{Z}_2$?
If there is a surjective homomorphism $f:\mathbf{Z} \to \mathbf{Z}_2 \times \mathbf{Z}_2$, then $\mathbf{Z}/\ker f \cong \mathbf{Z}_2\times \mathbf{Z}_2$. This contradicts something you know about quotients of cyclic groups.
Nov
21
comment If $G = \{g_1, … , g_r\}$ is abelian and $a = g_1…g_r$ show that $a^2 = 1$.
The elements of $G$ can be sorted in "pairs" of inverses, although some "pairs" will have only one member.
Nov
21
comment Understanding issue on demonstrating the congruences theorem
"$n$ divides $a-b$" is the usual definition of $a\equiv b \pmod n$, so what's yours?
Nov
21
revised Show that the problem of deciding whether a Turing machine prints something is undecidable
added 87 characters in body; edited tags; edited title
Nov
21
answered Show that the problem of deciding whether a Turing machine prints something is undecidable
Nov
20
comment irreducibility of a polynomial over $\mathbb{F}_2$
Berlekamp's algorithm is very good, you don't really need anything better than that. ;)
Nov
20
comment Prove F[X]/p(x) contains all roots of p(x)
It is in general not true, find a counterexample.
Nov
18
comment Let $n\in \mathbb N$. Prove that in $\mathbb{Z}_n$, $(\bar{a}+\bar{b})^2=\bar{a}^2+\bar{2}\bar{a}\bar{b}+\bar{b}^2$
You also do not use that $n$.
Nov
16
comment prove why RSA requires the use of distinct primes
This is the correct answer.
Nov
12
answered Where can I find the paper “Un théorème de compacité” by J. P. Aubin?
Nov
7
comment Can you recommend a mathematical logic textbook that is easy to understand?
Maybe the author and you have a different definition of "advanced math".
Nov
5
comment Solution of Congruence
Are you sure you need to find a solution, and not all solutions? In any case, this is called a linear congruence, just Google it, there are countless resources about it.