# All Questions

249 views

### OCB - brute force against unknown IV

I read that brute force attacks against a plaintext encrypted in OCB with unkown key and IV has approximately the same complexity as an attack where only the key is unknown. Why is that ? Is there a ...
983 views

### Known Plaintext attack against XTEA?

I'm looking for information on known-plaintext attacks against XTEA. I'm most interested in the worst case scenario: if an attacker has all 8 bytes of input and all 8 bytes of output, how much ...
9k views

### When to use RSA and when ElGamal asymmetric encryption

If i am not wrong in cryptography there are 2 basic cryptographic schemes for public key cryptography. RSA encryption whose security is based on the infeasibility of solving the factoring of big ...
356 views

### Key space size when either of two public keys are valid for authentication?

If for authentication a user can own either A OR B public key instead of just one specific key is that equivalent to halving the key space. i.e. it it theoretically twice as easy to brute force and ...
2k views

### Information leakage from the ecryptfs filesystem

I'm wondering what information might be leaked from the ecryptfs filesystem. This is what Ubuntu uses if you check the box for "encrypted home directory" when using the desktop installer, so is ...
660 views

### Can I safely replace XOR with ADD in a stream cipher?

In a stream cipher, the bytes of the plaintext are usually XORed with the keystream to produce the ciphertext. Would there be anything wrong with adding the bytes instead (with overflow), if adding ...
4k views

### How can one securely generate an asymmetric key pair from a short passphrase?

Background info: I am planning on making a filehost with which one can encrypt and upload files. To protect the data against any form of hacking, I'd like not to know the encryption key ($K$) used for ...
1k views

### Is SHA-256 secure as a CTR block cipher?

Generate a 256-bit random nonce. XOR it with a 256-bit reusable symmetric key. This is x. We represent numbers in simple binary instead of a counting function. ...
2k views

### What is the most secure hand cipher?

By "hand cipher", I mean a symmetric cipher for which encryption and decryption can can both be performed with a pencil on graph paper, consuming about 10-20 seconds per character by a proficient ...
853 views

### Is it possible to distinguish a securely-encrypted ciphertext from random noise?

Say I have a bunch of data encrypted with a secure block cipher (such as AES). An attacker has unlimited access to this encrypted data. The attacker doesn't know whether the data is encrypted or if ...
480 views

### Compressing EC private keys

For reasonable security, EC private keys are typically 256-bits. Shorter EC private keys are not sufficiently secure. However, shorter symmetric keys (128-bits, for example) are comparably secure. I ...
78 views

### Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]

Possible Duplicate: Two untrusted party want to exchange data: how to insure each one gets the data it needs? I am trying to come up with what could maybe be a novel algorithm for an ...
480 views

### Two mutually untrusted parties want to exchange data: how to ensure each one gets the data it needs?

I am trying to come up with what could maybe be a novel algorithm for an application I am writing. Client A has a file fA. Client B has file fB. Each party is untrustworthy and will try to rip off the ...
207 views

### Does the position of the salt improve its effectiveness when hashing?

Seems most documentation I have read suggests the salt should prefix the value to be hashed. Is this just for consistency, or is the salt more effective when prefixed?
590 views

### Is ISAAC considered secure as a cryptographic random number generator?

The ISAAC site claims it is secure, but I wasn't aware of any trusted 3rd party sources that verified its security.
2k views

### Would it be secure to use random numbers from random.org in a cryptographic solution?

Random.org provides true random numbers through an unsecured web service. Since these numbers would be transmitted in plaintext could they still be considered useful as true random numbers while ...
290 views

### Feedback on rolling my own entropy gatherer

First of all, I don't recommend doing this. This was something I created when I didn't know better and didn't have a solution available to me. Long ago I created my own entropy gather for a ...
2k views

### RSA cracking: The same message is sent to two different people problem

Suppose we have two people: Smith and Jones. Smith public key is e=9, n=179 and Jones public key is e=13, n=179. Bob sends to ...
2k views

### Is it possible to validate a Public Key in RSA?

If I have a 1024-bit number, and someone is telling me that it is in fact a valid RSA public key, is there any way I can quickly validate that it is indeed so (without cracking RSA)? (I suppose I am ...
406 views

### two public keys with same passphrase insecure? | can two hashes be compared?

Suppose someone had generated a 2.048-Bit RSA GPG/PGP key pair and published the public key on the usual key servers. Then he withdraws this key and generates a new one in 4.096-Bit RSA using the same ...
824 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 ...
481 views

### DES Crack simulation

I wish to simulate an implementation of a DES Cracker using verilog. But every paper I read give only abstract hints but no concrete steps or how really to go about it. How is it usually done? For ...
430 views

### Is it possible to create an easy to use encryption/decryption method that will never be comprimised?

In the comments of the question "Why programming languages don't provide simple encryption methods?" the following statement was made: A well thought out, tested and understood standard that has ...
1k views

### Cycle attack on RSA

I originally posted this question in the mathematics section, you can see it here. Let $p$ and $q$ be large primes, $n=pq$ and $e : 0<e<\phi(n), \space gcd(e, \phi(n))=1$ the public encyption ...
1k views

### Does AES-CTR require an IV for any purpose other than distinguishing identical inputs?

I'd like to encrypt files deterministically, such that any users encrypting the same plaintext will use the same key and end up with the same ciphertext. The ciphertext should be private as long as ...
1k views

### Why programming languages don't provide simple encryption methods?

In c#, there is a namespace called System.Security.Cryptography and there are many classes in this namespace, which help developers encrypt and decrypt data. ...
573 views

### Counter mode secure hash algorithm

Ever since the SHA-3 competition, I've been wondering if it is possible to create a hash algorithm that is easier to parallelize. The current algorithms all seem to require building a tree of hashes. ...
1k views

### How can I break REDSHIRT / REDSHIRT2 encryption?

Recently, a user on Gaming.SE asked a question about whether the user password in the video game Uplink could be modified after being initially set. The game does not contain an option to change the ...
321 views

### Why not use an algorithm's code rather than data itself for one time pads?

Instead of using actual data for one time pads, what would be different if the code for an algorithm was exchanged so that to acquire the pad one would execute the algorithm and use its output? Why ...
1k views

### Obtaining the key length from the ciphertext of an auto-encipher

I'm revising for a cryptography exam at the moment and I'm having some problems with a question. The question looks for the key length of a cipher given that the word "earthquake" appears in the ...
1k views

### Related-key attacks on AES

According to Wikipedia: Related-key attacks can break AES-192 and AES-256 with complexities $2^{176}$ and $2^{99.5}$, respectively. What are the requirements for these attacks (i.e how many ...
277 views

### In storing passwords in a database should I use a per-application salt in addition to a per-secret salt?

Assuming that the salts are sufficiently long (16 random chars) is there any advantage in using a per-application salt in addition to a per-secret salt when storing hashed passwords in a database? ...
237 views

### AESManaged Trade Compliance Issue in United States

I am currently using AESManaged encryption for my silverlight application. Does AESManaged encryption have a severe trade compliance issue in Bureau of Industry and Security in terms of shipping the ...
511 views

### Inverses in Truncated Polynomial Rings

I've been trying a long time to understand a thing which is obviously extremely simple, but I just can't get it. Read this, please: The NTRUEncrypt PKCS uses the ring of truncated polynomials $R$ ...
150 views

### Including a “purpose” designation in a digital signature

A signature of some data can mean many different things, such as: This is a message I sent, this is a certificate I validated,... So I was surprised that common signing schemes don't include a ...
452 views

### Families of public/private keys in elliptic curve cryptography

I'm looking for a related key scheme for elliptic curve cryptography. The basic idea would be that there would be a master public key and a master private key. From the master public key, you could ...
255 views

### How does one design a traffic analysis resistant protocol?

I'm curios about protocols which leak considerable personal information, like instant messaging exposing the contacts relation. How does one make an instant messaging protocol which is resistant to ...
157 views

### Does an attacker gain an advantage if they have the initialisation vector?

Does an attacker gain any advantage by knowing which initialisation vector was used for encryption?
277 views

### Does this block cipher mode allow for decryption?

Is there's a way for someone (with the key) to decrypt a message encrypted with the cipher mode shown? $$P_0 = IV$$ $$C_i = P_{i-1} \oplus E_K(P_i) \oplus P_i$$
464 views

### How close is homomorphic encryption to handling regular expressions?

Is there any reasonable homomorphic encryption protocol that supports some meaningful fragment of regular languages/expressions and/or edit distance bounds? I'm suspicious that homomorphic encryption ...
134 views

### How is the password sent across for verification?

I am familiar with Challenge-Response Authentication scheme. However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel. ...
7k views

### Why is AES resistant to known-plaintext attacks?

At least it's my understanding that AES isn't affected by known-plaintext. Is it immune to such an attack, or just resistant? Does this vary for chosen-plaintext?
293 views

### Verifying the integrity of ciphertext using the cleartext hash?

I want to be able to verify the integrity of a ciphertext by providing the cleartext hash, for this to work it would need to: $$hash(crypt(cleartext)) = f(hash(cleartext))$$ Where $f$ is an ...
497 views

### Can I determine if a user has the wrong symmetric encryption key?

We're using the Objectivity/DB object database with a custom encryption plugin that encrypts serialized objects on disk. Encryption uses AES with a shared secret key held by all users. I would like to ...
243 views

### How is de-synchronisation of HOTP solved?

From RFC 4226 I understand how HOTP generates one-time passwords by incrementing a counter and uses the 'look-ahead' window to try to resynchronise (from this counter), if the user tries a few wrong ...
268 views

### Is EKE attackable by a brute-force password search?

So I'm trying to properly implement the EKE protocol and I'm using C# with the Windows CNG and ECDH key exchange. I need to use this because it's FIPS certified and all that jazz. So what I'm ...
1k views

### What is the relation between Discrete Log, Computational Diffie-Hellman and Decisional Diffie-Hellman?

How are the three problems Discrete Logarithm, Computational Diffie-Hellman and Decisional Diffie-Hellman related? From my understanding, since the Discrete Log (DL) Problem is considered hard, then ...
492 views

### Creating a hash of XOR'd blocks

Suppose a message $m$ is divided into blocks of length $160$ bits: $m > = M_1 || M_2 || ... || M_l$ And define $h(m) = M_1 \oplus M_2 \oplus ... \oplus M_l$ Which of the three desirable ...