All Questions

1
vote
1answer
142 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
2answers
461 views

Can curve25519 keys be used with ed25519 keys?

Can curve25519 keys be used with ed25519? I'd prefer to use ed25519, but there isn't a fast java version. For my application, I'd like to use curve25519 until I can get a faster ed25519 for java. ...
1
vote
1answer
48 views

byte length and offset for k3d3/ed25519 byte[] variables?

I've discovered for myself that java's BigInteger is very slow, so I'm trying to weakly optimize this java implementation of ed25519 which I will fork and post if ...
2
votes
1answer
157 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 ...
0
votes
0answers
77 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 ...
1
vote
1answer
141 views

Regain 3DES ECB key, assuming I have both encrypted and decrypted text

Let's assume I've encrypted some text with some 24-byte key using 3DES in ECB mode. Is it possible to regain the key if I have both encrypted and decrypted text? (Excluding bruteforce.)
1
vote
0answers
126 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 ...
3
votes
2answers
277 views

Breaking a PRNG Scheme

Assume the following scheme for a PRNG generating decimals in [0,100) Given a message and a key, compute tag := HMAC512(message, key). Take the first 5 hexadecimal characters of the tag. If the ...
1
vote
1answer
201 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 ...
2
votes
1answer
136 views

Efficiently computing the neutral element in a ring isomorphic to Z/NZ?

Edited to clarify question So my question is whether anyone knows of an efficient way to compute the neutral element (I'm gonna call it 1, but the operation doesn't have to be multiplication) in an ...
1
vote
1answer
819 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 ...
3
votes
1answer
167 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 ...
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 ...
1
vote
1answer
268 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
100 views

Hashing entropy generator output with SHA256

I'm using SHA256 to hash the output of an entropy generator to generate random numbers. Is it generally better to treat the output of the entropy generator as single messages and hash each of those ...
1
vote
0answers
123 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 ...
6
votes
1answer
128 views

Are there groups where the computational Diffie Hellman problem is easy but the discrete log problem is hard?

I know that there are elliptic curve groups, used in pairing-based cryptography, where the decisional Diffie Hellman problem (ie. given $g$, $g^a$, $g^b$ and $c$, determine if $c = g^{ab}$ is easy but ...
3
votes
2answers
675 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 ...
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 ...
1
vote
1answer
113 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 ...
3
votes
1answer
169 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
1answer
181 views

How can I break this encryption scheme?

Let $p$ be a large public prime. Alice holds a private key $(e_1,d_1) \in Z_{p-1}^*$ such that $e_1 d_1 = 1 \mod {p-1}$. Bob also holds a different private key $(e_2,d_2)$ with the same property. ...
5
votes
2answers
85 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 ...
4
votes
1answer
117 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 ...
3
votes
1answer
134 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 ...
5
votes
2answers
202 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 ...
3
votes
1answer
105 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, ...
3
votes
2answers
223 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
1answer
75 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 ...
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) ...
5
votes
1answer
75 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
2answers
121 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 ...
2
votes
3answers
180 views

A specific way for deniable encryption

I read the summary of deniable encryption on wikipedia: https://en.wikipedia.org/wiki/Deniable_encryption Then I read a question, by doom123 on security.SE: ...
9
votes
3answers
802 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 ...
2
votes
1answer
71 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 ...
3
votes
1answer
291 views

Calculating amount of time for brute forcing ciphertext depending on the size of the key

I am a graphic design student and for my information graphic project I have chosen the topic of the history of encryption and how the security level developed over the centuries. It’s basically an ...
1
vote
0answers
97 views

Which is better ECDHE with TLS 1.0

I have a webserver which support only TLS 1.0 Which is the better cipher in this group for the best security? ...
2
votes
1answer
167 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 ...
1
vote
2answers
199 views

AES-CBC and IV — Encrypting multiple blocks of a file with the same IV?

I have large files which are broken into blocks of 512 KB and uploaded to a server. In my DB I store the IV, and the user knows the security key themselves. When downloading, I use the same IV and ...
1
vote
1answer
144 views

Is Bitmessage a Mix network?

I've read the Bitmessage whitepaper and I found it rather lacking on the details, but it promises anonymous routing. Can it be considered a variation on mix-networks, where each peer acts as a ...
1
vote
1answer
842 views

What is the difference between SHA256WITHRSA and SHA256WITHRSAENCRYPTION digest algorithms?

I installed djigzo on my android phone and I want to use it for smime mail. I don't know the difference between choosing SHA256WITHRSA and ...
2
votes
2answers
428 views

Json AES128: Security against known plaintext attack

I have a system where I am transmitting json messages securely (using for example AES-128), where each message has the same format. For example ...
3
votes
1answer
158 views

Password hashing in /etc/shadow

Passwords hashed under Unix/Linux systems can use several hashing algorithms. ...
5
votes
1answer
474 views

Diffie-Hellman Parameter Check (when g = 2, must p mod 24 == 11?)

I'm adding some Diffie-Hellman groups to a program as specified in RFC 3526, More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE). When I test some of the group ...
0
votes
2answers
949 views

Multiplicative inverse in $GF(2^8)$?

I know how to do multiplication over $GF(2^8)$. Logic is... ...
2
votes
1answer
70 views

Keyed-hash of a lot of small numbers

Let's say I have a list of several million numbers, with only 6-9 digits of secret information per number (this means that an attacker might efficiently guess the other digits). I have to store the ...
1
vote
0answers
105 views

Distributed integer factorization?

I'm looking around for publicly published work on factorization of large numbers using distributed systems of any kind. So far I've come across the PDF "Mapreduce for integer factorization" by Javier ...
2
votes
1answer
84 views

/dev/random only needed for key generation / CPU pattern encryption

Consider the following scenarios: using OpenSSL to encrypt a file with Rijndael-256 using LUKS to encrypt a hard-drive that is used every day Exactly when is entropy from ...
2
votes
1answer
101 views

Where can I find source code for ideal world simulation?

In many crypto papers I see they use a Real World / Ideal World Paradigm. However, I have never see the source code of such Simulators that try to simulate the adversary. Could somebody point me to ...
0
votes
0answers
70 views

Where can I find source code of a compiler that secures a circuit (or attemps to)? [closed]

In the paper “Multiparty Computation Secure Against Continual Memory Leakage”, on page 1239 under section “Using an LDS Compiler Instead of OCL Compiler”, the authors discuss why they decided to use ...

15 30 50 per page