5
votes
1answer
118 views

estimating entropy/randomness as fail-safe mechanism

Real-world encryption systems are often not broken algorithmically but because the implementation has a bug. Sometimes the bug only happens in circumstances that could not have been foreseen, such as ...
3
votes
2answers
542 views

ASCII to same-length ASCII encryption?

I need to encrypt an ASCII string [a-zA-Z0-9:] to an ASCII [a-zA-Z0-9] string of the same length. It doesn't have to be unbreakable, it's sufficient that it won't be readable at the first sight. The ...
11
votes
3answers
924 views

Are any of the major asymmetric ciphers distinguishable (EG, RSA, ECC)?

Related to "Is it possible to derive the encryption method from encrypted text?". Given ciphertexts generated by any of the major asymmetric ciphers (RSA, ElGamal, ECC, etc..) can these ciphertexts ...
2
votes
1answer
138 views

Shamir Secret Sharing Modular Reduction

Say players use Shamir's secret sharing to share a value $k$ such that each player now holds $k_i$, a share of $k$. How can they securely compute $k \bmod m$ for some $m$. Of course they can ...
10
votes
2answers
351 views

Is RC4 a problem for password-based authentication?

This is a follow-up question to Does TLS use RC4-drop[n]?. As mentioned in section 6 of RFC4345, there are weak distinguishers for RC4 keystreams available that even work for keystreams that ...
8
votes
3answers
822 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 ...
2
votes
1answer
163 views

Distinguishing attack on CBC-MAC

I want to ask about distinguishing attack on CBC MAC, as in the paper published by Ketting Jia, Xiaoyun Wang, Zheng Yuan, and Guangwu Xu: Distinguishing Attack and Second-Preimage Attack on the ...
2
votes
1answer
227 views

How much does a successful Distinguishing Attack “break” the attacked stream cipher?

I started reading about the most recent cryptanalysis of RC4 and it's variants. One of the papers I just finished reading ("Two Linear Distinguishing Attacks on VMPC and RC4A and Weakness of RC4 ...
2
votes
2answers
148 views

Impact of distinguishing between random text and cipher text?

In theory, distinguishing cipher text from random text is considered insecure for any PRP algorithm. Say for example - due to Patarin's proof with about six rounds of Feistel Network - the attacker ...
0
votes
0answers
76 views

Question Error Correcting Codes

Let $C$ be a code over the finite field $GF(2)$ with generator matrix $G$ and parity matrix $H$. Let $e+C=C'$ be a coset of code $C$. Let $S$ be a non-singular matrix and $H'=H\times S$. Finally, let ...
3
votes
1answer
105 views

How to protect against ephemeral key reuse in some signature schemes?

Given that some signature schemes (for instance Elgamal) use an ephemeral key that cannot be reused ever. How do people usually protect against this? I'll elaborate more: if you reuse the ephemeral ...
3
votes
1answer
153 views

TLS: Is Integrity assured when using NULL cipher

In specific implementation we're using TLS 1.0, open ssl 0.9.8 but i'm referring to RFC 5246. For performance reasons, I'm being asked if we can use TLS without encryption. The hope is that the ...
3
votes
2answers
466 views

Keeping IV secret for AES CFB mode

I'm developing a security/encryption software and I'm using AES CFB (block size: 16 and key size: 32 bytes). I want to know, if I also keep IV (32 bytes) secret like the key itself (32 bytes), would ...
1
vote
1answer
140 views

Question about SHA-2 (and potentially similar hashing algorithms)

I have been educating myself recently about the SHA-2 hashing algorithm, and in the midst of this pursuit, I've encountered a question: This algorithm uses a set of constant hexadecimal values, ...
2
votes
1answer
146 views

Using KDF output for password validation

I am currently revising an AES data format. I would like to determine whether a provided password/key is incorrect. Previously this was done by validating the HMAC, but this makes it impossible to ...
1
vote
1answer
193 views

Hash 22 byte secret into 512 bit hash: Full entropy?

Does it make sense to hash a 22 byte secret (which may not have full entropy since it is chosen by the user) into a 512 bit hash (using Keccak-512)? More precisely, will the 512 bit hash have full ...
4
votes
1answer
113 views

Encrypting a TCP connection between two unknown nodes

I'm writing an application for controlling computers from a client. I'd very much like it if the connection is secure and only authenticated clients are allowed access. The workflow will be ...
4
votes
0answers
136 views

Computing IV for CBC from PBKDF2 + HKDF

Note that this question is somewhat similar to Can I use my random IV (for AES) as a salt for PBKDF2? My current encryption format computes two random PBKDF2 salts (encryption and HMAC, 8 bytes each) ...
1
vote
0answers
120 views

inverse of scalar multiplier in ECC

I am learning to use ECC. i got into situation where i have $Q=abG$, where $G$ is the generator of the finite field formed on EC using a prime $p$ modulus and $a$ , $b$ are random numbers. now suppose ...
5
votes
4answers
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 ...
4
votes
2answers
166 views

Stream cipher with Diffie-Hellman and Cryptographic Hash Function?

(Already asked the same question on stackoverflow but I was told to better ask here. http://stackoverflow.com/questions/17527192/one-time-pad-with-dh-and-cryptographic-hash-function) I know: Never do ...
1
vote
1answer
627 views

How can i predict the next number of a long sequence of seemingly random numbers? [closed]

How can I accurately predict the next random number between 1 and 999, given past results. I have no knowledge of the PRNG or algorithm used. How can I predict the next number of a long sequence of ...
5
votes
2answers
72 views

What does it mean that $BW_N$ is a permutation over the squares mod N?

Let $BW_N$ be a function such that $BW_N:\mathbb{QR}_{N} \mapsto \mathbb{QR}_{N}$ and let if be defined as follow: $BW_N(x) = x^2 \pmod N$ where $N=pq$ and p and q are primes and $p=q=3 \pmod 4$. I am ...
6
votes
5answers
397 views

Asymmetric algorithm to generate compact unique messages that can be validated

I have a cryptographic problem with the following characteristics: I need to generate a set of relatively short messages; say 20 bytes in length The contents of the messages themselves is not ...
1
vote
1answer
243 views

AES mode for file encryption

I'm working on software that should eventually result in a crypto file system similar to encfs. So far, i have a user password that goes through PBKDF2 using ...
1
vote
1answer
111 views

Attack on BB84 algorithm for quantum key exchange?

I have a question which is related to the BB84 cryptosystem. We are not able to send single photons so instead we send $K$ photons at a time all with the same polarization. An enemy can separate one ...
1
vote
1answer
133 views

Recovering the random number r

For a padded message, M, using the El Gamal encryption schema, how can we determine the random number $r$, when we are given $p$, the prime number, $g$ which is the primitive root of $p$, $b$ and $x$ ...
9
votes
3answers
716 views

In what way is XXTEA really vulnerable?

I'm looking at using the XXTEA algorithm to encrypt a small amount of data (say, less than 32KB) in the context of a software licensing algorithm. That is, we wish to make it difficult (not ...
1
vote
0answers
118 views

Rabin code same message sent with different $N$

I use Rabin code with modulus $N$. Now assume that Alice sends me a message $m$ $(1\le m\le N)$ encoded by Rabin code. Unfortunately after Alice sent me the text I lose the information about the ...
7
votes
4answers
311 views

Automated security protocol verification tool for eCK model

I want a tool that (runs on Win7 and) can perform automated verification of a protocol in the eCK security model as described in Microsoft Research's paper "Stronger Security of Authenticated Key ...
2
votes
1answer
133 views

Which platforms are most vulnerable to Simple Power Analyse Attack

In a "Simple Power Analyse Attack", the difference in power consumption during multiply or square operation is used. In the RSA decryption process with the "Square and Multiply" algorithm, both ...
-1
votes
3answers
218 views

How to judge if my work is meaningful in cryptography? [closed]

Suppose I have generated a new cryptographical result - for example a new cryptographical primitive, or a cryptanalytic attack. How can I find out whether this result is meaningful (significant)? If ...
4
votes
1answer
138 views

Brute Force on 3DES with Reduced Keyspace and Unknown IV

I'm trying to brute force a 3DES problem given a reduced keyspace (ie I know the first half of the key) but with an unknown IV. The code decrypts to plaintext. My first thought was that I could set ...
3
votes
1answer
100 views

One-time pad mistake in the transmission?

I have a question which arised by analyzing the one-time pad cipher. I encrypt a binary sequence $a_1,a_2,..,a_N$ using a one-time pad with key sequence $k_1,k_2,k_3,...$, so I send $a_1+k_1, ...
5
votes
1answer
1k views

Low Public Exponent Attack for RSA

I'm having trouble understanding the algorithm for finding the original message $m$, when there is a small public exponent. Here is the example I'm trying to follow (you can also read it in the 'Low ...
5
votes
2answers
189 views

RSA cipher wrong use

Why is it foolish if you decide to use an RSA cipher to encode some message by first converting each letter of the message to an integer? So for exmaple Space=0, a=1, b=2,... After the conversion I ...
2
votes
1answer
199 views

ElGamal signature: Forging a signature of a specific form

I have a question I can't solve from one of the courses I'm currently taking: Show that given a legitimate ElGamal signature $(S,R)$ on a given message $m$, an attacker can compute a signature ...
3
votes
1answer
509 views

Java's SecureRandom & plaintext attack?

Java's SecureRandom is meant to be cryptographically secure, and I know part of that means that the output should not be usable to predict further output. Though, ...
1
vote
0answers
60 views

Looking for alternative key stretching

I am by no means a security expert, but I am curious whether functions that don't produce different outputs when raised to the power of N (without any psuedo-randomness) exist, that are as strong as ...
3
votes
1answer
152 views

Is SHA-256 safe when used in this way?

I am wondering whether an attacker can gain any useful information from having several hashes of an unknown plaintext that differs in relatively few bits. For example, if provided with: ...
5
votes
2answers
83 views

Why is this authentication procedure using Rabin crypto not useful?

A friend asked me the following, pointing out that the method is not very useful (my problem is I do not see why it is not good): Consider a person A which chooses $n$ as the public key for the ...
3
votes
1answer
126 views

AES: Is it safe to encrypt same cleartext with same key but with million diferent IV?

The encryption mode that I am using is CBC. Algorithm is AES and the key size is 128bit. I will be encrypting a 36 byte string over 1.3 million times with the same key but with a random IV. My ...
6
votes
2answers
96 views

Does having multiple hash iterations of the same message weaken your original message security?

Take a hash function H() to be something like SHA-256 and message m. If you are given H(m) ...
3
votes
2answers
173 views

What was the problem in the SSL version 2.0?

What is the main reason (attacks) the appearance of the protocol SSL version 2.0 to replace version 3.0?
2
votes
2answers
120 views

How to ensure that a “received value” is not altered?

I have a program (whereby people can download and run on their own computers) that will calculate a couple of unknown values each day. For simplicity sake, let's assume that the calculation is simply ...
5
votes
1answer
74 views

What is significance of recovering the chaining value of a hash compression function?

What is significance of recovering the chaining value of a compression function, when the message and its output are known? in other words, if a compression function $CF$ takes a chaining value ...
2
votes
1answer
72 views

Digicipher and other proprietary systems?

I've always been curious as to how Pay-TV and other Conditional Access systems actually stay secure for any amount of time, given that they are usually one way and (I'm assuming) use symmetric keys ...
2
votes
1answer
157 views

what's the advantages of identity-based systems over certificate-based ones?

Actually, I'm not familiar to how identity-based and certificate-based systems work, so ,can anyone give me a detail and comprehensive answer to this question? Moreover, in what environments the ...
3
votes
1answer
519 views

How do I generate a session key using the Diffie Hellman algorithm?

How to generate a session key between two nodes in two different subnets when the nodes don't know each other directly, using diffie hellman algorithm?
2
votes
1answer
68 views

Implementation of modular arithmetic?

In FIPS 186-3 appendix D.2 "implementation of Modular Arithmetic", they show shortcuts for solving $$B = A \mod m$$ for select Curves. How would you go about determining a valid short cuts for the ...

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