2
votes
3answers
467 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
314 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
691 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
677 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
351 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?
2
votes
1answer
343 views

Security analysis of a “one-time pad” type hill cipher

Suppose the Hill cipher were modified to something like a one-time pad cipher, where Alice wants to send a message to Bob, and she chooses a key matrix randomly everytime a new message is sent (and ...
5
votes
1answer
97 views

In a lattice, how can one define a good basis and a bad basis?

When it comes to lattice based cryptographic systems, all the literature talks about, good bases and bad bases. How does one define what a good basis is and what a bad basis is?
3
votes
3answers
355 views

Is the new preprint “An Algorithm For Factoring Integers” by Yingpu Deng and Yanbin Pan worth reading?

I just discovered on the eprint server of the IACR the paper mentioned in the title. Scanning quickly over the paper I didn't find anything spectacular, so I doubt that their new(?) approach will be ...
4
votes
1answer
164 views

Signing a GCM MAC

If I encrypt a message with AES-GCM, is it safe to use the MAC as the hash in a DSA/RSA signature? That is, if someone knows the AES key and nonce, will they be able to generate a different message ...
5
votes
3answers
153 views

Is the $\ell$-Diffie Hellman Inversion easy when g is known?

From here they define the $\ell$-Diffie Hellman inversion problem as: Given $g^{a},g^{a^2}\ldots,g^{a^{\ell}} \in G$, compute $g^{a^{-1}}$ Would this problem become easy if the generator $g$ is ...
5
votes
1answer
2k views

How large should a Diffie-Hellman p be?

In a Diffie-Hellman exchange, the parties need to agree on a prime p and a base g in order to continue. Assuming some ...
2
votes
1answer
360 views

Offline anonymous electronic money systems and their cryptographical base

What anonymous offline electronic money systems exist and what are they based on? I know only one currently - eCash, based on RSA blind signatures.
4
votes
1answer
238 views

How to construct a zero-knowledge proof of a number of the form $n=p^a q^b$

Let $n = p^a$$q^b$ where p and q are distinct primes and a and b are positive integers. How to construct a zero knowledge proof that n is of such form? This is actually a homework problem with a ...
6
votes
1answer
895 views

Why was ISO10126 Padding Withdrawn?

Wikipedia mentions ISO10126 Padding has been withdrawn, but doesn't say why. Also there were no news reports about this, as far as I can see. Why was it withdrawn? Are there security flaws? Is there ...
4
votes
1answer
1k views

Sending KCV (key check value) with cipher text

I was wondering why it is not more common to send the KCV of a secret key together with the cipher text. I see many systems that send cipher text and properly prepend the IV to e.g. a CBC mode ...
3
votes
2answers
335 views

secure multiparty computation for multiplication

Suppose there are $N$ parties $p_j$, each with a binary $b_j\in{\{0,1\}}$. The problem needs to compute the multiplication of number of ones times that of zeros, that is, ...
2
votes
2answers
182 views

How can I store a combination of multiple pass phrases?

Let's assume we have 2 phrases, one is the real password from a user, and the other is generated from the real password and almost impossible to guess. You would need both to authenticate a user. What ...
3
votes
1answer
408 views

Can I secure my key by XORing it with a hashed password?

I'd like to build a simple password-protected symmetric key system. The key-creation process in my system operates as follows: The system creates a 256-bit key purely at random. The user chooses a ...
5
votes
4answers
295 views

Are derived hashes weakening the root?

Given a root hash root = H(plaintext) and two (or more) derived hashes h1 = H(salt1 + root) h2 = H(salt2 + root) would the ...
12
votes
3answers
479 views

What exactly is the impact of the hidden subgroup problem on cryptography?

I understand my group theory (allegedly), so I can make partial sense of The Hidden Subgroup problem: Given a group $G$, a subgroup $H \leq G$, and a set $X$, we say a function $f : G \Rightarrow ...
6
votes
1answer
313 views

Threshold Signatures for RSA and DSA

I have a few questions relating to threshold signatures: a scheme where $n$ participants hold a key share and any $t$ of them can conduct a protocol using their shares that results in a valid RSA or ...
7
votes
1answer
551 views

Standardized parameters for elliptic curve cryptography

When an elliptic curve-based cryptosystem is deployed, a single set of public parameters (consisting of a particular elliptic curve over a finite field as well as a generator of a prime order subgroup ...
6
votes
2answers
4k views

Rijndael vs. Serpent vs. Twofish: General comparison

Can anyone explain (or give a link to document about) why Rijndaal won the AES, especially comparing it to other finalists (Serpent and Twofish)? What criteria were used to make decision? Or is there ...
4
votes
1answer
395 views

Can one group the SHA-256 outputs depending on partial inputs?

Is it possible to predict a hash key based on half key? Let's have some example: I have 100000000 hash results, and they are generated by either ...
7
votes
1answer
356 views

Exposing RSA private-key data… bad?

We know that exposing $p$, or $q$ or $\phi(n)$ results in trivial attacks on RSA since they allow us to factor $n$ and to compute the private exponent $d$. In OpenSSL (and most RSA implementations) ...
3
votes
1answer
144 views

Is a using salt important when creating a hash data validator?

I am creating a service that will return an set of objects, which will be used by multiple systems. At the end of the process, one (or more) of the objects will be sent back to our system for ...
1
vote
2answers
462 views

Is Common Name encoded in the certificate?

When I make a certificate like so cd /etc/openvpn/easy-rsa/2.0/ source ./vars . /etc/openvpn/easy-rsa/2.0/build-key client1 Then ...
2
votes
3answers
261 views

Realize a MAC using a Pseudo-random function?

Given a pseudo-random function and assuming that we do not have any other tools, How can we construct a MAC? I believe this can be done. Would like to know if there is more than one way of doing ...
10
votes
2answers
894 views

How does the MOV attack work?

What exactly is the MOV attack, how does it actually work, and what is it used for? It's explained briefly here and I'd like to know what it is more / what is it fully used for.
3
votes
2answers
604 views

Passwords with same SALT. What does this mean?

If the same SALT is used for many passwords on a Linux server, in what way is that a security risk? Does the mean, that a user (which can change his own password) can calculate other users passwords? ...
6
votes
1answer
1k views

Why not use CTR with a randomized IV?

I'm currently reading the chapter of Cryptographic Engineering (Ferguson, Schneier, Kohno 2010) about block cipher modes of operation. They have recommended CBC with random IV instead of CTR due to ...
4
votes
2answers
1k views

How to attack a general polyalphabetic cipher?

I am able to decrypt vigenere cipher text using the index of coincidence and chi test. However out of interested how do you go about attacking ciphertext that was encrypted using a mix alphabet ...
4
votes
1answer
250 views

Undecrypt using the OpenSSL EVP API?

I'm writing a client-server encryption scheme for homework, and I've stumbled upon what might be a fatal blow to my current implementation. When using AES-256-CBC on the two sides, it's important ...
4
votes
1answer
1k views

How does PBKDF1 work?

I need some basic guideline on Password Based Key Derivation Function. PBKDF1 generates a key from password and salt using Hashing algorithm (like SHA1, SHA256, MD5). What is the step behind this?
2
votes
1answer
2k views

Secure way to transfer data over NFC?

I am currently writing a payment system to accept payment details from an NFC enabled smartphone (BlackBerry 9900) to a Windows client (C#.NET) I am currently having two issues relating to security: ...
6
votes
5answers
3k views

Why do we need asymmetric algorithms for key exchange?

In SSL protocols, both symmetric and asymmetric algorithms are used. Why is it so? The symmetric algorithms are more secure and easier to implement. Why are asymmetric algorithms usually preferred in ...
1
vote
2answers
778 views

suggestions for cryptography projects for an ece 3rd year student

I am an electronics and communication engg student currently doing my 3rd year second semester. i am interested in info coding and the security aspects of it. As an ECE student i want to know what is ...
4
votes
1answer
266 views

Best choice of finite field for AES on a 4-bit microcontroller?

As the finite field of $GF(2^8)$ are isomorphic to $GF((2^4)^2)$, $GF((2^2)^4)$ and $GF(((2^2)^2)^2)$, which of the fields is best suited and most efficient for 4-bit MCU and why? Would it be ...
3
votes
2answers
513 views

Does RSA padding have to be unpredictable if the payload is?

I'm trying to understand the precise requirements on padding when using RSA for encryption. Suppose Alice uses RSA to encrypt a payload $M$ that cannot be guessed (say, a random nonce): Alice send ...
5
votes
1answer
264 views

Anonymous trust/reputation system

Suppose there are 3 persons, Alice, Bob and Peter. They are identified by their pseudonyms (public RSA keys). Alice has a key Alice, Bob has ...
7
votes
1answer
803 views

How to better generate large primes: sieving and then random picking or random picking and then checking?

I'm writing an RSA algorithm, and am wondering what is the best and/or usual way to choose the initial prime numbers (p and q). I know of two methods to achieve this, one based on a prime number ...
2
votes
2answers
194 views

Is there a cumulative commitment scheme?

For a certain application I need a commitment scheme where each user could make a commitment, and a single verification operation could verify all the commitments simultaneously, faster than single ...
3
votes
1answer
313 views

What type of hash functions provides non-malleability of hash digests?

I want to use a hash function for commitments. I don't want an attacker to construct a commitment related to a previously published (but still unopened) commitment. A simple deterministic commitment ...
2
votes
1answer
816 views

Is RSA of a random nonce with no padding safe?

Consider the following protocol: Bob has a private RSA key $B_{priv}$, and Alice knows the public key $B_{pub}$. Alice wants to send confidential messages to Bob (no integrity intended). To send a ...
1
vote
2answers
649 views

Can md5 be used for encrypting data?

I know that md5 shouldn't be used for password hashing because of collisions and possibility of making dictionary attacks e.g. using rainbow tables. But what about ...
6
votes
1answer
3k views

How do I correctly derive a Key and IV?

Mainly I'm trying to understand how to correctly create the Key and IV for use with the .NET Implementation of AES (AesManaged class). This encryption code will be used in conjunction with existing ...

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