2
votes
0answers
318 views

Openssl implementation of improved sha1 hashing [closed]

I want to use the improved sha1 hashing algorithm from the Intel blog described here Intel sha1 hashing. Currently I am using Openssl sha1 hashing in my application. I wanted to know if anybody has ...
6
votes
2answers
257 views

Unit testing a library RNG and its seeding for practical security

Suppose I have a cryptography library that provides me with a black-box random number generator that is supposed to be suitable for long-lived key generation. (Under the hood it may be assumed to use ...
7
votes
3answers
843 views

Is RSA padding needed for single recipient, one-time, unique random message?

I want a way to encrypt files using this process: http://crypto.stackexchange.com/a/15 . That is: generate a random password, use that to AES-encrypt a file, and use an RSA public key to encrypt the ...
1
vote
1answer
235 views

ZKIP for Paillier public key correctness

I'm using the Paillier cryptosystem in a protocol similar to mental poker. In the beginning of the protocol, each player generates a Paillier public key $(n,g)$. Later in the protocol, a player may ...
0
votes
2answers
268 views

Factoring a polynomial over a GF [closed]

I have the following question: What polynomial, when factored over the field $GF (2^8)$ based on the irreducible polynomial that is used in Rijndael, will factor into all the polynomials in the ...
4
votes
3answers
736 views

Division in paillier cryptosystem

Is division possible in the Paillier Cryptosystem? i.e. given a the cipher-text $C$ of an integer $M$ the plain-text divisor $D$, and only the public key, can one compute the cipher-text of $M/D$ ?
1
vote
1answer
280 views

Which encodings have |encoding key| >> |decoding key|?

I'm looking for an encoding scheme that requires a very large encoding key E (>10MB) and suffices with a relatively small decoding key ...
7
votes
2answers
2k views

How to calculate an IV when I have a shared private key?

I'm working with a server/client system that has securely negotiated a private key. I need to encrypt/decrypt messages passing in both directions which are typically between 100 bytes to 100 KB. I'm ...
2
votes
1answer
95 views

Educational videos for security topics [closed]

Is there anything like the famous "sorting out sorting" video in cryptography/security. I am looking for some nice videos that explaines SSL, SET, IPSec, PGP, S/MIME ....
5
votes
2answers
336 views

Checking a key before actually using it

I have a block of data crypted using twofish with a key of 128 bit. The data must be accessed from a GUI, the user gives the key, the block is decoded and the real data is accessed. Problem is that ...
3
votes
1answer
201 views

Is a subset of a random set still random?

Suppose you have an infinite list of random bytes, and you select the first N bytes that correspond to printable ASCII characters. Is this list of N bytes still as secure (e.g. for the purpose of a ...
5
votes
2answers
283 views

Cost of attacking Mobile OTP with a fake server

You want to obtain a 74-bit secret $K$. There is an oracle that will provide you with the following value for several values of $T$: ...
2
votes
1answer
113 views

McEliece for streaming data

Under the assumption that there exists a real-world implementation of the McEliece scheme, could it be applied to streaming data as is? By that I mean in 'block cipher mode'? I've read that McEliece ...
2
votes
0answers
183 views

john the ripper, usages [closed]

As evident from the site of john the ripper, JTR example, john can be used for finding password form a unix machine passwd file. can JtR be used to crack password ...
2
votes
1answer
109 views

Secure Remote Protocol - Are these 2 equations equivalent?

I'm implementing the Secure Remote Protocol that is specified to have this equation for the parameter S, the premaster secret. ...
11
votes
3answers
1k views

What is the use of REAL random number generators in cryptography?

I understand the use of pseudo-random number generators. I am not getting mixed up between these and "real" random number generators. However, I don't understand for what a real random number ...
5
votes
2answers
1k views

128 bit hash with least chance of collision

I'm building a storage system for JSON documents where they are looked up on a 128 bit key. These JSON documents have a timestamp within them, but apart from that are user-entered data. These JSON ...
5
votes
1answer
128 views

If plaintext is random, how does it affect my choice of encryption algorithm?

I want to encrypt a key file, which is assumed to be truly random (generated with hardware RNG, for instance). Given that there are no patterns in the plaintext, what implications are there for my ...
5
votes
1answer
264 views

S-box Cryptanalytic Resistance

In DES, different S-boxes were tested for cryptanalytic resistance and the most secure one was chosen for the algorithm itself. How do different S-boxes offer different levels of security against ...
8
votes
1answer
754 views

How should I check the received ephemeral Diffie-Hellman public keys?

In my application I'm doing a DH key exchange, where both sides generate their own ephemeral key. No static keys are used. I am trying to make my application resistant against an active attack and ...
6
votes
1answer
226 views

Is the Representation Problem hard on elliptic curves?

The RP in ECC would be to find $a_1,\ldots,a_n$ (integers) given $P$ and $Q_1,\ldots,Q_n$ (points in the EC) such that $P = a_1 \cdot Q_1 + \ldots + a_n \cdot Q_n$. Is it hard when DH-like ...
3
votes
2answers
804 views

Why do all hash functions use big-endian data?

I've looked at several hash function specifications, and they all emphasize the need for big-endian byte ordering. Is there a reason for this that has to do with security, or is it simply convention?
4
votes
2answers
224 views

Is SHA1 secure with such many inputs Z that Z = constant secret X + variable public Y?

Let me ask whether SHA1 is designed to be secure for the following case. You compute each SHA1 of many strings,for example 1 million, where each string is a concatenation of X+Y , where X is secret ...
4
votes
1answer
464 views

How is BCrypt secure when it uses a static dataset for blowfish hashing?

I'm planning on using this Javascript BCrypt implementation, but as you can see in the code, it uses a 4KB precalculated dataset for the P and ...
2
votes
1answer
70 views

Are there any signature schemes that protect against collusion by multiple parties?

Say I want to verify the identity of Alice, but Alice could be colluding with Bob to fool me. Is there any way to verify Alice's identity and also be sure that Bob is not impersonating Alice, e.g. ...
1
vote
1answer
473 views

Is this fixed length MAC unforgeable?

Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$: On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
4
votes
1answer
245 views

Why does RSA give better security on longer messages?

I am trying to understand the notion of RSA security. Choosing a public exponent where $e = 3$ facilitates the calculations, considering that it is secure if the plaintext or message is long. If the ...
3
votes
1answer
99 views

Is the following scheme secure for different cipher

Let's say I have two keys K1 and K2. two messages M1 and M2 of the same length. Cipher (E,D) 3 ciphertexts: C11, C12,C22 where Cij = E(Ki, Mj) In situation ...
5
votes
1answer
644 views

How does a “Tiger Tree Hash” handle data whose size isn't a power of two?

Constructing a hash tree is simple enough if the data fits into a number of blocks that is a power of two. ...
2
votes
2answers
337 views

How to generate successive stream-cipher keys?

I've identified a weakness in a distributed simulation system I'm looking at, and I'm looking for some advice on how to fix it. Clients initially negotiate an authentication token with a login server ...
5
votes
1answer
967 views

Permutations of pseudorandom data

Assuming a bit string is deemed cryptographically secure, e.g. PRNG using AES in counter mode, can we equally assume any permutation of said bit string is also cryptographically secure? In a more ...
6
votes
2answers
415 views

Alternatives to FHE for secure function evaluation

As a followup to a previous question I asked which was more related to Fully Homomorphic Encryption (FHE), what other cryptographic methods are available for computing a private function on public ...
3
votes
3answers
439 views

Complexity of arithmetic in a finite field?

I am wondering what the complexities are of adding/subtracting and muliplying/dividing numbers in a finite field $\mathbb{F}_q$. I need it to understand an article I am reading. Thank you
3
votes
0answers
810 views

MD5 encryption in Windows batch script [closed]

I am making a script in Windows batch to have a registration and login system that stores the passwords in a SQL database using SQLite. I need a command line MD5 encryption program to encrypt the ...
6
votes
2answers
6k views

Difference between “Signature Algorithm” and “Signature Hash Algorithm” in X.509

What's the difference between the "Signature Algorithm" and the "Signature Hash Algorithm" found in an X.509 certificate? Why does it need a "Signature Hash Algorithm"? Edit: I'm creating the ...
11
votes
4answers
314 views

Do parts of a hash carry the properties of the entire hash?

When I need to generate unique id's based on some information hashing is typical choice. However, sometimes that id needs to be of a particular size. I've seen a lot of schemes (HMAC-MD5-96 in SSH, ...
4
votes
2answers
368 views

X.509 CSR: Why does CA remove signature?

I just read this article on Wikipedia: Certificate Signing Request I'm not a PKI or Crypto expert. As I understand, a CSR (certification request) is always signed by the PKCS#10-Request creator. ...
2
votes
1answer
213 views

Shannon entropy calculation: is $H(A|R·A) = H(A)$?

Suppose I generate a random $m×m$ matrix $R$, where each of its elements belongs to $\mathbb Z_n$. I ensure that $R$ is invertible in $\mathbb Z_n^{m×m}$. Now I take a non-random $m×m$ ...
3
votes
1answer
280 views

Security analysis of a matrix multiplication protocol

Suppose Alice would like to obtain the product of two mXm matrices i.e. A and B. Alice has A, whereas Bob has B. Since Alice does not want to reveal A to Bob, she chooses a mXm random invertable ...
4
votes
1answer
136 views

Does security under ROM imply exactly what?

I'm not sure I understand really the implications of proofs of security in the random oracle model. Does a proof of security in ROM translate to a reduction of security of the crypto-system to the ...
2
votes
1answer
170 views

RSA-OAEP versus RSA with Fujisaki-Okamoto construction

I was wondering why the Fujisaki-Okamoto construction (or one of its variants) is not (at least commonly) used with RSA to achieve CCA2 security? Does anyone know of any speed comparisons between RSA ...
2
votes
3answers
485 views

reverse of md5sum

This might be out of ignorance, I apologize, but how complex of a problem might it be to generate a file of size N whose md5sum is X? For example, ...
2
votes
2answers
237 views

Seeking special-use fingerprinting/hashing algorithm

For a project I wonder if there exists some kind of fixed-size checksumming/fingerprinting function in which based on this fingerprint given data block 1, it is easy to generate more data blocks that ...
19
votes
6answers
315 views

advances in usability for cryptography/authentication

I'm wondering if there have been any recent advances (say, the past 5-10 years) in human usability for cryptography and/or authentication? By that I mean something that makes it easier for an ...
5
votes
3answers
719 views

Is it safer to generate your own Diffie-Hellman primes or to use those defined in RFC 3526?

I was wondering if the prime numbers defined for use with Diffie-Hellman in RFC 3526 are more trustworthy than generating one's own, especially considering the recent Arjen Lenstra paper (Ron was ...
8
votes
2answers
2k views

What advantage does facebook's new encrypted access_token have?

When a user on facebook grants an app access to their account, an API key is issued to the app. This key is app and user-specific. This process is described in Facebook's developer documentation. ...
0
votes
1answer
73 views

How to take SHA-1 safely for my particular case?

Let me ask about my toy passwords generator program X5 which I want to improve. X5 uses a secret key and a public key to generate a password.Where any public key is supposed to be known to hackers in ...
3
votes
2answers
734 views

How do public key rings work in cryptographic applications?

I am wondering if there are any links to articles or resources available online, or explanations that you can give, that would help me to understand the concept of a public key ring, and why I might ...
3
votes
0answers
108 views

RSA security assumptions - does breaking the DLP also break RSA? [duplicate]

Possible Duplicate: Would the ability to efficiently find Discrete Logs have any impact on the security of RSA? I'm wondering if breaking the DLP, that is the basis for ElGamal and DSA, ...
3
votes
1answer
361 views

What is the computational cost of a public key certificate signature verification?

What is the computational cost of a certificate signature verification in terms of exponentiation, multiplication and other computation operations?

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