All Questions

97 views

What might be assumed about a PRF if the key has been chosen?

The defining feature of a PRF $f:\{0,1\}^k\times\{0,1\}^s\mapsto\{0,1\}^*$ is that, if the first parameter is selected at random, it should be indistinguishable from a function ...
101 views

Looking for a detailed example of proof by reduction

I'm looking for a very detailed example of proof by reduction. Say we have two or three protocols (that have been proven secure) and we construct a new protocol. We want to provide a proof of security ...
82 views

Group membership with unique anonymous claims

Is it possible to accomplish the following scheme? There is a Server (S) and many clients. Each client enrolls with S, exposing its real identity; S saves the real identity information in its ...
804 views

Which eliptic curves in OpenSSL 1.0.1f meet all / most of the SafeCurves requirements? [closed]

I am using nginx compiled with OpenSSL 1.0.1f (most current release available). Nginx allows administrators to set a configuration parameter called ssl_ecdh_curve, ...
245 views

Key expiration policy for 3DES / TDES / Triple DES

I have a system that signs plain text messages using a message authentication code (MAC) encrypted with 3-key Triple DES. The short message is used on connection to establish a session key, so it ...
266 views

Entropy of Androids motion-sensor data

My app on Android uses the built-in motion sensors to collect seed-data for the PRNG (java.security.SecureRandom) that is later to be used for key-generation. The user is told to shake the device so ...
94 views

What informal indicators exist for estimating the computational infeasibility of cryptographic problems?

When assuming a block cipher primitive is secure, or a number theoretic problem is hard, this assumption is usually based on how far we are from breaking the primitive or solving the problem using ...
107 views

How much plainext could be known without reducting security of RSA?

It is known, for example, that exposing 50% of most significant bits of RSA private exponent does not provide security risk (when a small public exponent it used). So how to qualify security ...
202 views

Prove preimage resistance property

Let $f : \{0,1\}^* \rightarrow \{0,1\}^n$ and $g : \{0,1\}^* \rightarrow \{0,1\}^m$. $h$ is created by concatenate f and g: $h : \{0,1\}^* \to \{0,1\}^{n+m}$ with $h(x) = f(x) || g(x)$. How do I ...
215 views

Increasing the diffusion of the AES-CBC encryption algorithm in pycrypto for python

When encryption is done using the AES-CBC algorithm, the encryption can be thought of as chaining the cipher texts with the previous ones and an IV. However, if its on CBC mode, we give our cipher ...
179 views

What aspects of information theory are used in modern cryptography? [closed]

In studying modern (and classical) cryptography, many notions from information theory crop up. Unicity distance, min-entropy, compression, encoding, etc. What parts of information theory should be ...
86 views

Why does the new encryption scheme proposed by authors stop an adversary from guessing the subspace of the secret key?

In this paper, the authors construct an encryption scheme that is supposed to be resilient to tampering and leaking (as opposed to just leaking). Specifically this scheme: If you look at the ...
91 views

Hi Sec National algorithm

I'm trying to create a remote controller compatible with HiSec algorithm. It's so old that National (now Texas Instruments) discontinued NM95HS01/02 and docs are unavailable. Does anyone have the ...
312 views

How can I prove/disprove that a construction yields a secure PRG?

Let $G:\{0,1\}^{*} \mapsto \{0,1\}^{*}$ be a secure PRG. Prove or disprove that the following construction also yields a secure PRG. $$G'(k) = G(k||0),$$ where $||$ denotes the concatenation of two ...
226 views

Logics for Cryptographic Information Games

Preamble: There is currently a zoo of various logics for evaluating (proving) security in cryptographic protocols. The idea is that, by expressing these protocols using some logic, you can create a ...
128 views

Which encryption method supports random reads?

I have a file containing 16-bit samples and I want to encrypt it, but the problem is that I need to be able to read any random 16-bit value from the file, and be to able to decrypt it, without reading ...
57 views

CBC with random prefix but no IV - secure? [duplicate]

I'm looking at a datagram-based protocol that encrypts a payload. The payload is encrypted with AES or blowfish in CBC mode, and the result is then authenticated with a HMAC. To save space, the ...
217 views

Using single EC cert/keying material to derive symmetric encryption key (for storage)?

The situation involves a single party (single certificate) who would want to AES encrypt a file that they can later decrypt. Assume the EC certificate + EC keys have a purpose i.e. "File encryption" ...
131 views

Designing a protocol to record attendance to lectures

Scenario: a class that is not mandatory. The teacher wants a protocol that will satisfy the following requirements: It must record each student's attendance. A student X should not be able to say ...
114 views

Question about proof of knowledge defintion?

I am just reading the "soundness"-definition for proofs of knowledge by Bellare / Goldreich. A proof of knowledge is a proof between a prover $P$ and a verifier $V$. $P$ convinces $V$ to know a secret ...
86 views

Is SHA-1 collision free on data up to 20 bytes long? [duplicate]

Is SHA-1 collision free on data up to 20 bytes long (lenght of hash / internal state)? That means that every input produce unique output, but you surely know that, i just write it in order my question ...
112 views

CBC with fixed IV but changing data [duplicate]

Possible Duplicate: Using CBC with fixed IV I am using AES in CBC mode. For some reasons I have some issues for transmiting the IV. So I am using a fixed IV. If the first 128bits of the ...
170 views

Does Keccak have an eTCR mode?

On page 7 of NIST's views on SHA-3's security requirements and Evaluation of attacks, I see that, at least at this point, NIST planned on offering SHA-3 having eTCR security (defined on page 3): ...
323 views

RSA reencryption scheme

Is there such an algorithm that would allow to upgrade the encryption of a RSA-encrypted message without revealing the plaintext to the untrusted user? Basically, such an algorithm would probably be ...
812 views

Elliptic curve cryptography related key attacks

This question is an extension of Families of public/private keys in elliptic curve cryptography As described above, bitcoin "type 2" deterministic wallets use a root private/public key pair, where ...
938 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 ...
115 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, ...
170 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: ...
170 views

Zero Knowledge Example using discrete log

I've been exploring Zero Knowledge Proofs and while the classic cave example by Jean-Jacques Quisquater makes sense, I find the discrete log example problematic. Since the Verifier is given p, g and ...
195 views

Measure ECC key size

I have implemented a ECC key generation scheme successfully. Now I need to find ECC key sizes of each generating key pairs. I assumed that ECC key size is the size of the ECC private Key. So I would ...
280 views

Reordering non-block-aligned parts with DES in ECB mode

I was given a ciphertext file which was encrypted using DES in ECB mode. It is known that the plainttext that was encrypted has the following form: Each line of text consists of a payroll followed ...
165 views

Alternative sources of random numbers

Considering that algorithmic methods for generating unpredictable streams are hard to come by, I've wondered if any of these potential sources are good for making keys, seeds, and the like: stocks, ...
3k views

“123456” and “password” as crack standards

I know that when we encrypt, we use standard encryption technologies and to store data it's often stored as a hash. By encrypting a common password, for example "password" using ...
2k views

Using one-way hash functions as the encryption method

Suppose two parties want to communicate securely with each other (Bob and Alice) using a simple messaging system in English. There are approximately 180,000 currently used words in the English ...
587 views

Implementing a one-time pad without binary?

This is a program that I found which takes a purely alphabetical message, converts the letters to their ASCII values and combines them with the ASCII values of an alphabetical key (wrapping around ...
527 views

How to submit a new method of encryption?

I came up with a truly new method of applying modulo-2-addition encryption function in stream ciphers which is inspired by a mechanism used to prove a mathematical theorem. How can I determine whether ...
235 views

Difference between statistical PRNG and cryptographic PRNG?

What's the difference between a statistical pseudorandom number generator (PRNG) and a cryptographic-strength PRNG? I've seen a lot of PRNGs that are proposed for statistical uses -- e.g., ...
1k views

Is python a secure programming language for cryptography?

I know Python is a powerful programming language but is it secure for cryptography? I mean is it possible to reverse engineer the program (written in python) and discover the algorithm of cryptography ...
448 views

Does AES CTR mode store header information in encrypted files?

According to the movable-type.co.uk website, In the ‘counter mode’ used in this implementation, a counter which changes with each block is first encrypted, and the result is bitwise xor’d with the ...
710 views

How to perform Multiplicative Inverse Modulo in IDEA

How to perform the Multiplicative Inverse Modulo in International Data Encryption Algorithm? I don't understand on how to perform it… For example, let's say I have a value of ...
764 views

Would this simple encrypted chat program be feasible using One Time Pads?

Lets say I want to build a simple chat program that has encryption that is impossible to crack for anyone, even a theoretical government with a massive super computer. Ok here's my idea. You'll need ...
169 views

Isn't the structure of a potential plaintext of a ciphertext generated by a one-time pad dispositive, cryptanalysis-wise?

That is, if I generate every possible result, and analyze the structure against, for example, a dictionary, won't that identify which of the solutions in the domain is most likely the correct one? I ...
2k views

Malleability attacks against encryption without authentication

Suppose there is a message that is encrypted with AES-128-CBC. The message is as follows, new lines are used to delimit the 16 byte boundary for each block: ...
393 views

Does AES with whitening mode have the following property?

This mode is that each time a random number $K$ is generated, you XOR it with plaintext $M$ and then pass the result to AES. Since AES is a pseudo random permutation, does AES have the following ...
1k views

How does one scale encryption strength upwards from 256-bit?

I have seen many examples of encryption up to about 256-bit. But how does one programmatically scale the logic upwards in a language such as PHP or Java to say 1024-bit or even 4096-bit and higher? ...
1k views

Why is the private key generated first in public key crypto?

I'm still new to public key crypto. I'm trying to understand how it is that the private key is generated first in public key crypto? I would have expected the private and public key to be generated at ...
462 views

SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?

Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?
676 views

Encryption vs. decryption of same plaintext

Does the same encryption algorithm given the same plaintext always produces the same ciphertext? Does this cause any security flaws?