# All Questions

1answer
278 views

### Non adjacent form of an integer is unique

I have tried to look up the proof for NAF (Non-adjacent form) being unique for every integer, but as far as I have seen, textbooks only mention it as a property of NAF, but no proof is given. Also I ...
1answer
43 views

### Use of Lamport's Signature as a primitive

Is Lamport's One Time Signature used as a primitive to construct any other cryptographic protocols?
2answers
449 views

### Does SRP reduce to DH key exchange when shared password is not secret?

I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later. I ...
1answer
173 views

### Asymmetric cipher with multiple public keys

Asymmetric cryptography is well known. You generate a private key. Using the private key you generate a public key. Then you can sign a message with the private key and check signatures using the ...
4answers
446 views

### Password length versus hash length?

If a system hashes passwords with a 256-bit long hash, are passwords (which are not necessarily alphanumeric, can be any value per byte (0-255)) longer than 32 bytes useless under the context in which ...
1answer
297 views

### Where is the authentication tag stored in file encrypted using AES-GCM?

So I am using cryptopp to encrypt a file in a project and I am using AES-GCM. I have a 256bit key and a 128bit ivec and a 128bit tag that I use to encrypt files. However, I want to know where the ...
1answer
290 views

### How does ROTL work?

what does ROTL stand for? I know it does left shifting but what about the acronym? When we do a left shift, do we take the leftmost bit and add it at the end, by making the second bit the first, and ...
1answer
188 views

### Adding two public keys

secp256k1 (the signature scheme used by Bitcoin) has the interesting property that you can add two public keys to get a combined key that requires both private keys to produce signatures for. Is ...
1answer
26 views

### Key iteration count while using random keyfile larger than master key

If I were to have a 4096-bit file of random data (/dev/random) used as a keyfile for LUKS, would there be any benefit to having a key iteration count higher than 1? My reasoning is that the attacker ...
1answer
227 views

### SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)

The hashing scheme SHA-256 (for instance) is based on Merkle-Damgard construction with the underlying compression function based on the block cipher SHACAL-2 configured in Davies Meyer mode. SHACAL-2 ...
2answers
490 views

### SHACAL in SHA-256

I was reading about hash functions, namely SHA, and I read that it is made of the Merkle-Damgard construction. And then the text said that the compression function used is based on the Davis-Meyer ...
1answer
33 views

### Figure 2 in the Verifiable Computation - Pinocchio

I am reading the Pinocchio paper (verifiable computation): http://research.microsoft.com/pubs/180286/pinocchio.pdf The paper is rather hard for me. For the Figure 2, I guess $v_1(x)$ should be ...
1answer
79 views

### Can a cryptographic hash be used as a cryptographic RNG?

Say I roll a six sided die 200 times (6^200 = ~2^517) and string all the results together into a long string of numbers and hash then result with SHA-512. Can I use that result for cryptographic ...
1answer
63 views

### Is this transposition cipher information-theoretically secure for 1 message?

Given: $m = \{0,1\}^{n}$; a plaintext message of length $n$ encoded in binary $k = randomshuffle([0, 1, ..., 2n-1])$; A secret key consisting out of unique numbers between 0 and $2n-1$ in a true ...
1answer
326 views

### RSA: Why must e be relative prime to phi(n) [duplicate]

I've got a question concerning fields used in RSA: Let's use the following symbols for my example: {p,q} = primes {e,n} = public key {d,n] = private key I learnt that an inverse element exists if a ...
0answers
55 views

### How to securely map an element from an smaller domain to the other element in a large domain

Problem: I have a small sized domain, say s-bit. It's clear that the probability for an adversary to guess an element is $\frac{1}{2^s}$. I need to make the probability negligible. However, I need to ...
2answers
213 views

### Has human-generated entropy ever been a real problem?

I know the topic of human brains generating random numbers has been discussed here and in Cognitive Sciences before, but I am interested in a particular part of it: In an introductory book to ...
1answer
89 views

‎ ‎‎please help me what is number of invertible matrix $‎m*m$‎‎‎ on Group $\mathbb{z}_n$ ?‎‎‎, assuming we know‎ this number in $\mathbb{Z}_p \quad$ (‎p is prime‎‎) is $‎(p^{n}-1)(p^{n}-p) ... 1answer 76 views ### Which one these alternatives using authentication and encryption will solve this multiple-user database problem? Which one these alternatives using authentication and encryption will solve this multiple-user database problem ? I'm trying to understand the field of cryptography, so I've started reading a ... 2answers 2k views ### Why does second pre-image resistance imply pre-image resistance I am studying hash functions. I can understand why collision resistance implies second preimage resistance, but I don't get why second preimage resistance should imply first preimage resistance. ... 2answers 3k views ### Multiple private keys for single public key I am currently working in security in mobile ad-hoc networks. I have several clusters, and I want to send some data encrypted with its public key, from the cluster head to the cluster members. I ... 1answer 41 views ### What is the signifcance of inside threat in “How to Construct Multicast Cryptosystems … Secure Against CCA2” In How to Construct Multicast Cryptosystems Provably Secure Against Adaptive Chosen Ciphertext Attack, the paper states under preliminaries: We consider the scenario where a single party, called ... 1answer 81 views ### Swap$x$and$k$in GGM construction I'm studying the Goldreich-Goldwasser-Micali construction from pseudo-random generators to pseudo-random functions. In this specific construction, assume$G:\{0,1\}^n\rightarrow \{0,1\}^{2n}$is a ... 1answer 156 views ### Linear Recurrence, keystreams, and periods I am trying to understand the following problem: Consider the following linear recurrence over$Z_2$of degree four:$z_{i+4} = (z_{i+3} + z_{i+2} + z_{i+1} + z_{i}) \bmod 2$i >= 0. ... 0answers 48 views ### Generating interactive, secure multiple ECC key pairs deterministically In Elliptic Curve Cryptography (ECC) assuming user A has a private public key pair of$S$,$P$accordingly with generator point$G$which as we know is: $$P=S*G$$ Assuming that user A wants to ... 1answer 65 views ### How are onetimepads distributed? OTP encryption is unbreakable as it seems. I have read some stuff (wiki, blogpost, etc.) but i would not find any information how they are used. If i wanted to create a messenger service, how would i ... 0answers 76 views ### Is the reverse of the “discrete logarithm problem” equally dificult? [duplicate] It is not easy to understand why this becomes a hard problem. The discrete logarithm problem as defined here: “any integer k that solves$b^k = \{g\mod{n}\}$is termed a discrete logarithm” i.e.: ... 1answer 316 views ### Proving the existence of a pseudorandom function I've been reading the Introduction to Modern Cryptography book by Katz and Lindell as part of my own learning and have come across this exercise which I am not sure how to approach. The exercise is: ... 1answer 100 views ### How to generate the APA SBox? I am trying to generate the S-Box provided in the Affine Power Affine paper (PDF) but I'm not sure I understand it fully. The essence of the paper is this: ... 1answer 55 views ### Deterministic outputs based on non-connected inputs I am looking for a one way function that can generate outputs deterministically. However, revealing any of the inputs dont allow the person to generate other inputs. E.g: lets say we have a list of ... 1answer 264 views ### Multiple AES/ECB encryptions of different data with same key all end with same pattern We have used "AES/ECB/PKCS5Padding" with a 256 bit key. We encrypt different streams of data (blockwise) with the same key. Each encrypted stream ends with same pattern. What is the reason for this? 0answers 56 views ### Determine encryption method with input and output A website stores username and password in a session cookie. In the cookie the password is "encrypted" or modified in some way. Given that the "encrypted" version is always the same, I do not believe ... 1answer 77 views ### Key distribution and computation for homomorphic encryption How can a system where the party performing a computation also possess the private key and still not know the answer of computation be designed ? Also the other party who does not have the private key ... 1answer 75 views ### SSL certificate / SSL configuration - FIPS-197 compliance What does it mean when we talk about FIPS-197 compliance in the context of SSL certificates, their deployment and usage ? I am almost certain that the FIPS-197 compliance in the context of SSL ... 2answers 596 views ### How does a certificate authority issue a digital certificate? I am new to cryptography and I want to know the details of how a Certificate Authority issues a digital certificate. From what I know (please correct me if I'm wrong at any parts of my explanation): ... 2answers 12k views ### How is XOR used for encryption? I am a programmer, so when I hear XOR, I think about the bitwise operator (e.g. 0110 ^ 1110 = 1000). The mention of "XOR" comes ... 2answers 389 views ### Why isn't CTR mode (counter mode) used more often? For the CTR mode, the design is good for parallelization, yes, it seems the benchmark of the program downloaded from crypto++ proves that on an Intel I7 CPU. My question is that as most of CPU on ... 1answer 115 views ### Verification of Pinocchio (verifiable computation) I am reading the Pinocchio paper. The calculated result$y$is a part of the verification input, but it seems to me, the verification procedure does not utilize the result$y$. Can anyone can help me ... 1answer 143 views ### Beginner question about secure communication with one user using DES I am currently learning about encryption and I was asked a question: If a customer only had a DES system how could I secure messages as DES is not secure. I was researching this and I came across a ... 1answer 260 views ### Super-simple encryption of short strings I want to anonymise the initials of experiment participants by giving each a pseudonymic set of initials, by encrypting their true initials. Their initials are only two or three letters in length. ... 0answers 96 views ### side channel attacks against TDES (compared to AES) We all know AES has some pretty strong side channel attacks, some where (with a couple of hundred know plain- and ciphertext combinations) a key can be derived in a matter of minutes. Others may take ... 1answer 225 views ### Elliptic curve cryptography G*G I understand how ECC works for the point multiplications and stuff. All we normally do is to multiply a scalar number (lets say d as a private key) with the base point generator ... 1answer 147 views ### Known plaintext attack on 3 round SIMON block cipher I am attempting to write a program to perform a linear approximation attack on a reduced round version of the SIMON block cipher, but I am stuck on how to actually apply the linear approximation to ... 0answers 52 views ### Cache Attacks on Cloud Infrastructures I read something about cache attacks like this: Enter KSM (Kernel SamePage Merging). KSM enables the kernel to examine two or more already running programs and compare their memory. If any memory ... 1answer 2k views ### How does ECDH arrive on a shared secret? I read a brilliant, three part article on Elliptic Curve cryptography (one, two, three). It was able to explain Elliptic Curves to me in a way that didn't require a math degree to understand. The ... 2answers 367 views ### Is SSL getting faster because it's getting less secure? There has been some discussion about it being more practical to use SSL due to advances in hardware. From my understanding, stronger public-key encryption means that both encrypting/decrypting and ... 1answer 206 views ### what are the NTRU keysize and application in industry ? I'm a student currently working on a research project on the NTRU cryptosystem, I've read some papers about this cryptosystem, and in those papers they are talking about keysize, is it the size of the ... 1answer 58 views ### Why rogued certificate from hash collision is harmful I cannot understand why rogued certificate is thought harmful though It can be used to impersonate some website. The attacker can craft a rogued certificate with different identities and public key ... 1answer 56 views ### Different keys for clients but 1 key on server Is it possible to have different keys on alot of (embedded) devices and just have 1 key on a server (to witch all these devices connect)? The main point here being when 1 device is compromised this ... 1answer 130 views ### What is SHA-256 in Conjunctive Normal Form? What is the conjunctive normal form (CNF) representation of$\text{SHA-256}(m)=h$, where$m$is of fixed (or bounded) size and$h\$ is 256 bit?

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