5
votes
1answer
932 views

Get RSA PlainText without Knowing Private Key

If I have an algorithm,RSA-Crack(), that, for a given RSA public key (n,e), is able to decrypt 1% of the messages encrypted with that key (without knowledge of the corresponding private key).Can there ...
10
votes
1answer
4k views

Compare Blockmode CBC (with diffuser) against XTS

I have some problems in understanding the "advantage" of AES-XTS compared to CBC with diffuser. I read something about FileVault, in this paper they mention the two modes of operations XTS and CBC ...
1
vote
2answers
290 views

Non-Interactive Zero-Knowledge-Proof for discret Logarithm?

In a Non-Interactive $Zero-Knowledge-Proof$, the challenge is chosen by the Prover. I am trying to find a Non-Interactive Zero-Knowledge-Proof based on the following problem: DISCRETE LOGARITHM ...
2
votes
2answers
418 views

How can I add more rounds to AES?

I'd like to understand a bit more about the AES key schedule if anyone would mind explaining that. For instance, why is the way the schedule generated (with recursive xors and occasional ...
2
votes
1answer
172 views

Comparing plaintext to contents of ciphertext

Given an authenticated mode of encryption, when comparing a plaintext string against the contents of a ciphertext, which approach is typically considered safer? Encrypt the plaintext and compare ...
3
votes
2answers
273 views

Two step encryption

Is there any asymmetric cryptography algorithm which will allow recursive encryption. ...
1
vote
1answer
228 views

Does RSA-OEAP have integrity and authenticity properties?

RSA-OAEP is IND-CCA2 secure (indistinguishable under an adaptive chosen ciphertext attack). Does it also have the INT-CTXT (integrity of ciphertext) and INT-PTXT (integrity of plaintext) properties? ...
4
votes
1answer
583 views

In RSA encryption, does the value of e need to be random?

I am a novice programmer and am just finishing up an RSA encryption program that I am writing for practice. Currently I have the program generate a relatively small random value for the public key e. ...
1
vote
0answers
160 views

Sigma-protocol for 3SAT problem

I have some questions from previous years exams, I hope you could help me with them. :) Let $g,h$ denote generators of a group $G$ of large prime order $n$ such that $\log_g h$ is unknown to anyone. ...
4
votes
2answers
279 views

AES encrypting multiple files

So if I want to encrypt all the files in a folder with AES (same password) I take each file and generate the key schedule using PBKDF2. As the PBKDF2 algorithm takes in a salt then this salt should ...
2
votes
0answers
168 views

Transforming simplest protocol into a Sigma-protocol

I have some questions from previous years exams, I hope you could help me with them. :) Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) ...
1
vote
2answers
136 views

What is an easy method of proving that a cryptographic oracle attack is possible?

Lets say an application is using CBC mode without authentication. The application is generating cipher text. This cipher text can be manipulated by the attacker and then transmitted back to the ...
1
vote
1answer
383 views

AES Secure key generation and storage

I have a client-server application, which is transferring data between its components in a secure way. I currently use AES algorithm with CBC mode to transfer data and file. This is the scenario: ...
7
votes
2answers
217 views

Is there any research on the problem of making a number more memorable to humans?

Authentication protocols often rely on humans dealing with large numbers correctly. For example, when a user logs into a remote machine using SSH for the first time, she is prompted to confirm that ...
1
vote
2answers
150 views

Bent Combining Functions

Bent functions are boolean functions with maximum nonlinearity and are widely studied for their potential applications in cryptography. Lets say you wanted to use a simple two input AND gate as a ...
3
votes
1answer
157 views

SSL Key Exchange

I read briefly over the TSL/SSL key exchange protocol. I have to wonder about the whole pre-master-key procedure. Wouldn't it be sufficient if the client or server encrypted a generated session key ...
1
vote
1answer
106 views

Ensuring integrity of a client side script

I want a script that is running on the client to compute a collision resistant hash and send it to a server. I need to ensure that the script which performs this hash is not altered in any malicious ...
8
votes
2answers
1k views

Webcam random number generator

I have a question about random number generators. I have read from a real random number generator, based on a webcam ("randcam"). My problem is, that I do not really understand how the generation of ...
1
vote
1answer
630 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 ...
4
votes
1answer
108 views

Security implications of using constant string to verify AES key?

I know that you can use for example CBC-MAC to verify data integrity and thus the password upon decryption. But would there be security implications of just adding a constant string to the plaintext ...
2
votes
1answer
206 views

What is an oracle adversary?

I'm trying to figure out block ciphers and this is the first time I've encountered the term "oracle adversary". It appears in the context of defining a PRP and a PRF. Can someone please explain what ...
3
votes
2answers
455 views

Stopping timing attacks on AES: Why is it important to prevent the OS from interrupting the AES computation?

I read the paper Cache-timing attacks on AES (by Daniel J. Bernstein), but I don't seem to understand everything. The author dedicates a long section on how to prevent the OS to interrupt an AES ...
4
votes
1answer
428 views

Exhausting the entropy of a hash function

In the case of password storage, consider the following: I have an idea that one can exhaust the entropy of input to the MD5 function by using a 128 bit random value as the password (indeed, any hash ...
2
votes
1answer
336 views

What's a good P to use in ElGamal key generation?

I need to generate a 1024 bit ElGamal key on Android, and key generation takes forever (~10 minutes on a Galaxy Nexus), I suspect because it take so long to generate a safe prime. Is it dangerous for ...
4
votes
1answer
743 views

AES timing attacks

I'm just interested in cryptography, so please don't expect me to be an expert. ;) I recently read about AES cache timing attacks and found it very interesting. I read the article Cache-timing attacks ...
-4
votes
1answer
156 views

Can someone tell if my Hand Cipher is secure? [closed]

In easy steps, this is how it works: Convert txt to numbers. mod 1-26. Generate random numbers (by my other cipher) equal to plain txt. Write random numbers under txt numbers. Like this: ...
3
votes
1answer
2k views

Constructing RSA private key, given public key

As part of a puzzle I was given an RSA 256-bit public key and an encrypted message. The key itself is very weak, having exponent e = 65537 and modulus N = ...
-1
votes
1answer
197 views

Does a playlist of songs or movies mixed together contain enough random enough for OTP key material?

Ok hypothetical scenario. Lets say I want to generate a lot of key material quickly for a one-time pad. This key material will be divided up and used for many different messages in the future. I ...
2
votes
3answers
222 views

Message authentication codes construction

I was reading the paper $[1]$ and came across the scheme that I show below. While I understand the scheme well, I don't understand why they prepend a 0 to the block containing $r$ and a 1 to all other ...
2
votes
2answers
254 views

What cipher mode is suitable for independantly decryptable short messages?

I'm building a small VoIP client which transmits encrypted audio data via UDP, and some packet loss is expected, so each packet will need to be decrypted separately even if others in the stream don't ...
2
votes
2answers
303 views

The security proof for Key Policy Attribute Based Encryption

My question relates to the original KP-ABE paper: http://research.microsoft.com/en-us/um/people/vipul/abe.pdf I'm having trouble understanding the proof (pages 10–13) that the scheme is secure in ...
3
votes
1answer
202 views

Why does Schnorr's Digital Signature scheme necessitate two prime numbers?

One of the necessary components to the Schnorr Digital Signature scheme is a pair of prime numbers p and q such that q divides p-1. However, there is never a modular inverse taken of q so why is there ...
8
votes
1answer
870 views

Necessity for finite field arithmetic and the prime number p in Shamir's Secret Sharing Scheme

Shamir's original paper (PDF, 197kb) describing a threshold secret sharing scheme states: To make this claim more precise, we use modular arithmetic instead of real arithmetic. The set of ...
4
votes
4answers
320 views

How to prove membership of a list without disclosing the list members?

I'm designing a messaging system where the sender A sends a message m with a signature s to n Receivers. A Receiver Ri should then be able to prove to a Verifier V that he is one of the receivers of ...
2
votes
3answers
356 views

Safety of DSA key parameters sharing

I'm looking for a solution to use in a context where I need to be able to generate new asymmetric key pairs quickly (using a widely recognized algorithm, and EC-DSA is not applicable). It sounds like ...
2
votes
1answer
2k views

Brute force attack on DES + property of DES

In a brute force attack on DES, it seems to me that one plaintext-ciphertext pair suffices to launch the attack. (I.e. suppose we are given a message $x$ and a ciphertext $c$ such that $DES_k ( x ) = ...
0
votes
2answers
449 views

Is the AES encryption scheme CPA secure?

Give a 256 bit key space and 128 message space would AES block cipher as the encryption scheme be CPA secure?
3
votes
2answers
155 views

Is there an advantage to storing keys split between several hashes?

I have a question about the way to store a key or password that was used for encryption, so that the application can check if the user put in the right key for decryption. If I make a mistake, please ...
0
votes
1answer
515 views

Learning cryptography using a FPGA

I have a FPGA and am curious what cryptographic applications I can use with it. I'm just a hobbyist / security researcher and not a professional cryptographer. Since I'm creating my own curriculum, ...
3
votes
2answers
396 views

Looking for examples for “proof by reduction”

Im looking for examples for a proof by reduction. For example: Let $A=(Gen, H)$ be a hash function. We define a new Hash function $A'=(Gen',H')$ with Gen=Gen' $H'_s(x)=H_s(H_s(x))$ It should be ...
1
vote
2answers
194 views

Pseudorandom generator and AE-secure encryption

How would you answer the following question (I have to translate it from German): The existence of a pseudorandom generator implies the existence of a AE-Secure encryption scheme (AE = ...
7
votes
4answers
578 views

Cracking WWII-era codes - code found on a pigeon's leg in Surrey

A recent BBC article entitled WWII code 'may never be cracked' posted a code: AOAKN HVPKD FNFJW YIDDC RQXSR DJHFP GOVFN MIAPX PABUZ WYYNP CMPNW HJRZH NLXKG MEMKK ONOIB AKEEQ WAOTA RBQRH DJOFM TPZEH ...
-2
votes
1answer
391 views

Encrypting with private key in Public Key InfraStructure [closed]

In Public key infrastructure, the MD5 of a piece of data is encrypted with the private key of a sender and this encrypted MD5 – along with the data – is again encrypted using an algorithm like AES or ...
16
votes
3answers
7k views

Should we sign-then-encrypt, or encrypt-then-sign?

We often want to send messages that are both (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active attackers ...
3
votes
2answers
1k views

Cracking the Beaufort cipher

Is there any easy way to crack a Beaufort cipher? We have a Vigenère table, and are trying to guess the keyword. Any easier way?
5
votes
2answers
712 views

Does a trace of SSL packets provide a proof of data authenticity?

I'm wondering if it would make sense to record a whole HTTPS session, publish its encryption keys and present it to third parties as a proof that this particular data was sent by a given server ...
3
votes
0answers
168 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): ...
4
votes
1answer
235 views

Questions about William's p+1

First off, if you're doing William's p+1 test, then also doing Pollard's p-1 is redundant, since the p+1 test covers both cases, right? Second, why is the recurrence $V_{n+1} = aV_n - V_{n-1}$ used? ...
10
votes
3answers
474 views

How to construct a good PRF from a block cipher?

We want to explicitly construct a good (as tentatively defined below) Pseudo-Random Function $F$ with $b$-bit input and output, from (preferably just) one Pseudo-Random Permutation $E$ of $b$-bit, as ...
4
votes
2answers
268 views

Is storing the hash of a key together with ciphertext encrypted with that key secure?

Is it secure to store the hash of a symmetric cipher key along with data encrypted with that key? Are there any circumstances or algorithms in which this combination could lead to potential weaknesses ...

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