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1answer
103 views

Who's talking to who encryption - does this concept work?

With all the NSA stuff in the news, I've been thinking about how to ensure the "who's talking to who" is just as private as the contents of the messages. I had an idea on the subject, about which I've ...
1
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1answer
193 views

Security Consideration on The Use of Random Number in Digital Signature

key-exchange protocol allows two parties to establish a shared key over public network. Lacking of authentication the original Diffie–Hellman key exchange is insecure under man-in- -the-middle ...
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1answer
919 views

Proper way of doing encryption and authentication (PBKDF2 + AES)

I'm currently in the planning phase of an authentication and storage-ish service. The client needs a file ("ENCFILE") which he will work with. This file will be encrypted with AES256, and stored on ...
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1answer
193 views

Is the “secure-as-worst-case” version of NTRU patented?

Does the improved version of NTRU — which is described in "Making NTRU as Secure as Worst-Case Problems over Ideal Lattices" by Stehlé and Steinfeld — fall under the same patents as the original?
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1answer
332 views

What's wrong with my security model - or how can it be attacked?

I'm working on a little personal project where security is very important, and I've thought for a while about the best way to do this. Now I am looking for a little outside help on good practices. The ...
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1answer
217 views

PKCS#11: Can C_GetMechanismInfo() return CKR_OK on a disabled mechanism?

According to PKCS#11 v2.20, "C_GetMechanismInfo obtains information about a particular mechanism possibly supported by a token." Does that mean ...
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1answer
180 views

The “Square Root” Solution of Oblivious RAM Simulation

I am reading the paper Software Protection and Simulation on Oblivious RAMs by Oded Goldreich and Rafail Ostrovsky. And I wonder about the description of the "Square Root" solution of oblivious RAM ...
1
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1answer
626 views

Discrete log problem with modulus prime

I am a bit confused on the hardness of the discrete logarithm problem. Does it become intractale only when it is mod n, where n is a large composite number (Like RSA key). What about if it is mod a ...
1
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1answer
96 views

Send a message to an entire group of recipients

I'm attempting to send a message to a group of recipients, through an untrusted intermediary. Each of the recipients will have been invited to the group by someone who already has a trusted public ...
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1answer
302 views

is this authenticated key exchange protocol sound? too complicated? obviously flawed?

(significantly reworded this question to fit better into crypto.se). I have static RSA keypairs for both sides and an encrypted transport that needs symmetric keys, and need to exchange session keys. ...
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1answer
694 views

Algorithm for proving Carmichael numbers

I have an application for determining if a number is a prime or not, currently I'm getting a random number, then doing the Fermat primality testing to find out if the number is probably prime (so this ...
1
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1answer
453 views

Four-Square cipher and its keyspace

Am I thinking about this correctly? Consider that the keyspace of the Playfair cipher is equivalent to all permutations of the alphabet, e.g. the number of distinct permutations of 25 objects, and ...
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1answer
411 views

RSA padding: what is it and how does that work?

If I am not mistaken, plaintext RSA is not secure. So, I have read that padding and hashing is needed to make the RSA algorithm secure. However, I am confused on what does padding or armoring mean in ...
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1answer
113 views

Merkle signature + PRNG?

In the section 3 (page 44) of the book "Post Quantum Cryptography", it says: Then each one-time signature key must be generated twice, once for the MSS public key generation and once during the ...
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1answer
103 views

constructing QR-like one way function

I am wondering whether the following form is a one way function with collision resistance: $$ax^2+by^2 \mod p$$ where $a$ and $b$ are given, and $p$ is a prime number. Since the QR (quadratic ...
1
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1answer
206 views

Tor's integrity verification system?

I am trying to understand the design of Tor(onion router). I am reading the original paper on the 2nd generation onion routing system. Where, under integrity checking on streams, they say, "When Alice ...
1
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2answers
492 views

How practical is proxy re-encryption for AES?

In proxy re-encryption schemes, a proxy is given special information that allows it to translate a ciphertext under one key into a ciphertext of the same message under a different key. How ...
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1answer
260 views

Preimage resistance hash in digital signature

I'm studying about preimage resistance property of the hash functions. In particularly I'm reading as the missing of this property can be fatal in digital signatures that use RSA. Further details: ...
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2answers
128 views

Differential privacy definition

Differential privacy defines "privacy" of a mechanism $A$ as the "closeness" of the two distribution $Pr[A(D) \in S]$ and $Pr[A(D') \in S]$ where $D,D'$ differ in one element. And the distance between ...
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1answer
134 views

What kind of cryptography should i use?

I have a trusted third part A that issues an access token (xml file) to an untrusted client C that uses this token to log into an untrusted server S and access to the authorized files. I want only ...
1
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1answer
542 views

Smart Card Basics

I want to implement some of the basic encryption algorithms on smart card, could any body guide me how to program a smart card, which tools (hardware and software) I should have, and if these tools ...
1
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1answer
543 views

When making public key fingerprints - is a sha1 hash still a good idea?

I'm thinking about trying to save some space (and readability) when referencing 2k and 4k public keys (millions of them) by storing the fingerprint in some places instead of the full public key. ...
1
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1answer
77 views

Why does the server in S/KEY authentication only store a single password?

I've been reading about the S/KEY One-Time Password system on wikipedia here and was wondering why the server only stores a single password and not the list of one-time passwords like the client does. ...
1
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1answer
447 views

Key sizes for discrete logarithm based methods

I have a question regarding the key generation process of methods that are based on the discrete logarithm problem. This site gives some good insights, but I don't fully grasp it I think: ...
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1answer
215 views

Elliptic Curve is DH function or PKI?

can we reuse same ECC key on TLS for long terms or it must be used just once? (i mean can we use ECC like RSA?) is there patent free ECC implementation ?
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1answer
94 views

Adversary Two Stages

I am read this paragraph and I have a doubt. "An adversary to PKC $\Pi$ is given by two probabilistic polynomial time algorithms, $A = (A1; A2)$. In the first stage, the "find" stage, the ...
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1answer
85 views

What does “securely realize” mean?

I was wondering what "securely realizes" means. I see this in some cryptographic papers but I don't know what it means for a protocol to "securely realize" a function $F$. Is it just a fancy way of ...
1
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1answer
3k views

AES AddRoundKey

Looking at the first step of AES encryption I see that we XOR the key with the plaintext block. Why is the actual key involved at all, why not just use the round keys derived from the key schedule?
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1answer
75 views

What is the significance of i^Q mod P = 1 and are there any special properties to be aware of?

I'm studying UProve, and one of the fundamental components of this technology is based upon the relationship between i^Q mod P = 1 Lacking a specific name I can call this mathematical ...
1
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1answer
286 views

Use curve25519 for ElGamal crypto [duplicate]

DJB described curve25519 in his paper which can be found here (PDF). It seems that the main purpose was for Diffie-Hellman key exchange. I think this means that Discrete Log is supposed to be hard on ...
1
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1answer
140 views

Security relevance of random factor in Paillier

In the Paillier cryptosystem [1] the encryption of $m \in \mathbb{Z}_N$ with randomness $r \in \mathbb{Z}_n^*$ is $c = g^m r^n \bmod{n^2}$. The additive-homomorphic property of the system shows that ...
1
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3answers
908 views

What goals is homomorphic encryption aiming to solve?

As I understand from this article about homomorphic encryption, it mainly aims to enhance the security of cloud computing. We should be able to encrypt data and send it to the cloud. After it is send, ...
1
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2answers
922 views

Deriving HMAC key and cipher key from passphrase? [duplicate]

I'm encrypting a file with AES-256 in CBC mode. I needed to add an HMAC for authentication and validation of the file contents and passphrase, so I used a SHA-256 HMAC over chunks of my file ...
1
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2answers
1k views

Fastest multiplication algorithm for efficient exponentiation in C++?

First I apologize if this question is better tailored for SO, but since I'm using the method for crypto stuff, I thought I'd ask anybody that might know here. Karatsuba algorithm does a pretty good ...
1
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1answer
365 views

Measuring Shannon's diffusion

Shannon's idea of diffusion is fundamental to cryptography. Besides being a descriptive idea, is there any work on measuring or expressing it? Saying something like "System A has more diffusion than ...
1
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1answer
214 views

Request for 1024-bit primes $p$ , subgroup $q$ and subgroup generator $g$

I need to find a prime $p$ of $1024$ bits with a $160$ bit sub group size $q$, such that $q|p-1$ , and $g$ is the generator of the sub group size $q$. I'm looking for the numeric values of $p$ , $q$ ...
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3answers
1k views

Kryptos : K2. What is the origin of the “abscissa” keyword?

I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4. Similar to the "palimsest" keyword for K1, the keyword "abscissa" for K2 was determined by brute-force. To better ...
1
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1answer
332 views

Understanding padding oracles - is an attack plausible in my scenario?

I have a scheme that, long story short, uses AES in CBC mode to encrypt third-party credentials for user accounts with a password-derived key. It's been mentioned that the use of CBC mode is a ...
1
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1answer
188 views

inverse element in Paillier cryptosystem

As I know, in Paillier cryptosystem, the encryption $c$ of a message $m$ is calculated as $c=g^m r^n \bmod n^2$. Now, I am wondering if I can derive $g^m \bmod n^2$ given that I know $c$, $r$, and ...
1
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1answer
181 views

Factorize RSA knowing several N and E

I did a CRT challenge yesterday and there`s one problem I was unable to solve, probably due to my lack of understanding advanced crypto math. It`s about RSA. There are ten given pairs of N and E ...
1
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1answer
861 views

Weakness in using only one RSA key pair for two-way communication?

In Alice/Bob/Cindy terms (EDIT: and with a little more detail): Alice and Bob have each securely obtained one key of an RSA keypair from a trusted third party. Alice has one key ($e$ and $n$), Bob ...
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1answer
2k views

How does a client verify a server certificate?

As far as I know, when I request a certificate from Verisign (for example), and after they approved that me is me, they create a certificate (for me) which contains the digital signature and public ...
1
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1answer
2k views

Blowfish: hex digits of pi used for s-boxes?

Preface: here is the official site for the Blowfish algorithm: http://www.schneier.com/blowfish.html The Blowfish algorithm uses an s-box, which consists of hex digits of pi (found here: ...
1
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1answer
372 views

How can I prove in zero knowldege that an ElGamal shuffle is correct for a special setting? [closed]

In a special ElGamal encryption scheme, every user has an ElGamal encryption key-pair using the same cyclic group $G$ and generator $g$. The system has a special function : $$ ...
1
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1answer
364 views

Real world use cases of Multi Party Computation

Most of the research papers give imaginary applications of multi party computation. Either they talk about millionare's problem or two or more corporates willing to compute some Intrustion detection ...
1
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1answer
109 views

Is secure remote snap possible?

Scenario: We have a central server $S$. We have a number of peripheral servers $P_i$ We have some individuals $U_j$ A given individual may be "known" to one or more peripheral servers. Each ...
1
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1answer
127 views

Conditional entropy

Suppose I have a file with random binary strings of the same length in each line. If I'm computing the conditional entropy $H(Y|X)$ where $Y$ is the variable string of fixed length $l$ which is ...
1
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1answer
119 views

How to hide bit frequency of the inter-packet delays covert channel?

I encode a hidden message as different delays between packets of another data stream. My implementation now is that for each bit, if the bit is 0, a inter-packet ...
1
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1answer
392 views

Can iterated key expansion in Blowfish slow down bruteforce attacks on small key sizes?

Suppose I have to use 64-bit keys for encryption (e.g. to comply with export restrictions). For this question, assume this key is truly random, and the encryption algorithm is Blowfish. Blowfish key ...
1
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1answer
719 views

Cryptanalysing Affine cipher

I am trying to cryptanalyse a cipher–text encrypted by Affine cipher. The encryption formula is: $c = f(x) = (ax+b)\bmod m$, where $a$ and $b$ are unknown constants; $x$ is a plain-text symbol, and ...

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