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Questions tagged [cryptography]

Questions on the mathematics behind cryptography, cryptanalysis, encryption and decryption, and the making and breaking of codes and ciphers.

Please only post questions about the mathematics of cryptography here.

  • Coding and implementation specific questions should go to Stackoverflow with encryption or cryptography tags.
  • You may also consider asking at Cryptography Stack Exchange which is for asking questions about the mathematics and properties of cryptographic systems, their analysis ("cryptanalysis") and subsidiary topics that generally make up cryptology.
1915 questions
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Finding valid keys in a cryptosystem (m^k + mod 41)

I'm studying for an exam I have tomorrow and could not find the answer to the following question: For which of the following values of k is $$ E_{k}(m) = m^{k} mod 41 $$ a cipher over $$ Z_{41} $$ ? And the possible values of k is: 3, 5, 7
John Adams
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AES S-Box Cycles and Matrix Representation

I would like to know how many cycles the Rijndael S-Box consists of. Ideally expressed as a product of k-cycles in standard notation. Also, given that the AES cipher is totally linear without the permutation step, does it mean the decryption routine…
user11393
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AES Key Scheduler

How do you get the rcon for AES's key scheduler? Where does it come from; is it a constant because it seems to differ?
Will03uk
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Generate Public Key of GGH Cryptosystems

I have a question for the algorithm gen public key of The Goldreich–Goldwasser–Halevi (GGH) lattice-based cryptosystem. GenKey Algorithm as described in the paper: Pick a matrix $R'$ which is uniformly distributed in $\{-l,\ldots,l\}$ and then…
Phương Thu
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Permutation OTP perfect secrecy proof

Let $M$ be a finite message space. Recall that a permutation on $M$ is a bijective function on $M^2$. Assume that permutations can be encoded/decoded and transferred efficiently. Prove that the following scheme has perfect secrecy: KeyGen : Sample…
Hannah
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DSS crypto algorithm confusion

Here is the exercise: Suppose that $(p,p_1,g_1,a)=(107, 53,4,13)$ is the public key for a digital signature and $(52,47),(29,7)$ are the signatures of the messages $m=15$ and $m'=12$, correspondingly. If $k,k'=2 k$ are the daily keys that have been…
dmtri
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Why is this signature independent of the message?

Assume that we have the following signature scheme CL Signature: Choose a cyclic group $G = \langle g \rangle$ of order $q$. Uniformly and randomly choose two elements $x,y \in \mathbb{Z}_q$, and compute $X = g^x$ and $Y = g^y$. The secret key is…
Bean Guy
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RSA: What message will Alice receive?

In RSA, Alice chooses $p=47$, $q=57$, public key ($n=2679$, $e=11$). When Bob sends the message $m=3$, what is the message that Alice will read?
SSMath
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if $a b \bmod n = x$ then is it true that $x b \bmod n = a$?

I am a student of computer science and I'm doing cryptography; I need to optimise the way I calculate modulus. What I'am doing is like this: $$14 \cdot 16 \equiv 3 \bmod 17$$ $$3 \cdot 16 \equiv 1 \bmod 17$$ My question is if that is true for all…
you
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Can a nondeterminstic algorithm preserve privacy?

How can we define $\epsilon$-differential privacy for non-deterministic algorithms?
Joe Zhou
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Linear matrix cryptosystem

You intercept the following message: $VOBG!?FRWZ?RPAGYJFGWX?$ which was sent using a linear matrix cryptosystem $[x, y]^{T} \rightarrow A[x,y]^{T}$ on digraph message units (i.e. each unit consists of two symbols) in the 29-letter…
Swayy
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RSA in practice

I know how decryption and encryption in RSA works when I have a plaintext $m$ represented as an integer. But how will (in practice, not in theory) a text be converted into an integer? I guess there has to be a method that is used universally, or…
Martin
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Generated RSA Modulus and Private Exponent appear invalid

I have a generated public/private key pair 2048 bits that is from windows software from a reputable large company but the Modulus and/or private exponent seem to be invalid. The file generated is an XML which has private keyblob, public keyblob, (D…
Sealdogfish
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Describe the set of rational points on the curve

Describe the set of rational points on the curve $x^2-7y^2=2$ Given that $(3,1$) is on the curve
badosky
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Books for pure cryptography.

I am trying to find a"good" book (or a series of "good" books) which covers the following parts in cryptography: Some background (such as Number Theory, Finite Fields, ) Classical cryptography (I would say private key cryptography) Public key…
Lecter
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