All Questions

1
vote
1answer
283 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
114 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
135 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 $x$ ...
10
votes
3answers
876 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
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 ...
7
votes
4answers
320 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
149 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
219 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
170 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
106 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
2k 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
210 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
210 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
595 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
179 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
90 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
140 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
98 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
256 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
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 ...
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
1answer
77 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
181 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
545 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
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 ...
1
vote
0answers
100 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? ...
1
vote
2answers
215 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 ...
0
votes
2answers
1k views

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

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

Is this new server API authentication protocol secure?

I need a secure protocol to authenticate client side users with my server which has an API. I am devising something more secure particularly to resist active MITM attacks where an attacker may modify ...
2
votes
1answer
101 views

Ephemeral Diffie-Hellman generator selection

I need to generate a EDH group on the fly in one has not been specified in a config file. Diffie-Hellman is kind of expensive in terms of computation, so I'd like to reduce the cost if possible. Is ...
5
votes
1answer
498 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 ...
2
votes
1answer
103 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 ...
1
vote
1answer
984 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
449 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 ...
10
votes
1answer
526 views

What is the theoretical and practical status of mental poker?

I'm able to find a lot of scattered papers on the development of mental poker since RSA proposed the initial solution but no recent report (i.e. after 2005) on what is the status of the problem, eg: ...
23
votes
3answers
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 ...
3
votes
1answer
164 views

Password hashing in /etc/shadow

Passwords hashed under Unix/Linux systems can use several hashing algorithms. ...
2
votes
1answer
72 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 ...
0
votes
1answer
108 views

Oracle DBMS_RANDOM algorithm?

Oracle DBMS offer builtin random number generator (pseudo to be accurate). DBMS_RANDOM is one of the available packages, it is however considered as insecure for cryptography. Do we happen to know the ...
1
vote
0answers
24 views

Why does a joint leakage MPC protocol not directly apply to a disjoint leakage requirement?

In the paper "Multiparty Computation Secure Against Continual Memory Leakage" on pg. 1239 the footnote at the bottom points out the difference between $joint$ leakage and $disjoint$ leakage. The ...
2
votes
1answer
85 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 ...
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 ...
1
vote
1answer
123 views

Decryption honeypots

When performing a key search, I've always wondered how you reliably detect a successful decryption once you hit the right key. I assume that you have to analyze the data and look for patterns: words, ...
10
votes
1answer
6k views

Calculating RSA private exponent when given public exponent and the modulus factors using extended euclid

When given $p = 5, q = 11, N = 55$ and $e = 17$, I'm trying to compute the RSA private key $d$. I can calculate $\varphi(N) = 40$, but my lecturer then says to use the extended Euclidean algorithm to ...
2
votes
3answers
179 views

EC equivalent for RSA-OAEP

I have some questions regarding aforementioned subject: Is there a EC equivalent of RSA-OAEP key transport/encryption algorithm ? Is ECIES-KEM sufficient ?
4
votes
1answer
315 views

Coefficients in Shamir's Secret Sharing Scheme

Sorry if this is a stupid question, but: in Shamir's scheme, we construct a polynomial and make our secret $S$ the zero-th coefficient $a_0$. What, if anything, necessitates this - in other words, can ...
0
votes
2answers
540 views

FIPS 140-2 compliant algorithms in Enhanced RSA and AES Cryptographic Provider (Windows XP) [closed]

We have a native C++ application that supports Windows XP SP3. Recently we've decided to change our crypto algorithms to FIPS 140-2 compliant ones. We are planning to use the following algorithms in ...
0
votes
0answers
23 views

How to understand the Bilinear mapping with an example [duplicate]

An efficient bilinear map is given by $ e $: $G_{1}$ × $G_{1}$ → $G_{T} $. How can i prove this equation with the help of an example.
1
vote
2answers
220 views

Encrypt and decrypt data accessible by multiple users within a team

I'm currently working on web services which allows to send and retrieve data. The data belong to a team. A team is composed of users. Each authenticated user can send and retrieve data to/from their ...

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