All Questions
6
votes
1answer
300 views
Can a user of a password-protected Wi-Fi sniff on other user's communication?
Imagine a Wi-Fi network protected by WEP/WPA/WPA2. Users can join the network in case they know the pre-shared key of the access point.
Is it possible for a user A (who has successfully logged into ...
1
vote
0answers
190 views
Openssl implementation of improved sha1 hashing [closed]
I want to use the improved sha1 hashing algorithm from the Intel blog described here Intel sha1 hashing. Currently I am using Openssl sha1 hashing in my application.
I wanted to know if anybody has ...
8
votes
1answer
239 views
Making ECDSA public keys one bit shorter
In compressed form, ECDSA public keys are one bit larger than the curve size. There are some situations where this extra bit is extremely inelegant. So I had the following idea as a way to remove it.
...
5
votes
3answers
345 views
How to authenticate over open channel?
I am making an arduino project to open my garage door. I want to make it so users with the passphrase can open the door. Due to computational restrictions it is unlikely encryption is possible. ...
5
votes
3answers
427 views
Is RSA padding needed for single recipient, one-time, unique random message?
I want a way to encrypt files using this process: http://crypto.stackexchange.com/a/15 . That is: generate a random password, use that to AES-encrypt a file, and use an RSA public key to encrypt the ...
1
vote
1answer
147 views
ZKIP for Paillier public key correctness
I'm using the Paillier cryptosystem in a protocol similar to mental poker. In the beginning of the protocol, each player generates a Paillier public key $(n,g)$.
Later in the protocol, a player may ...
1
vote
1answer
147 views
Which encodings have |encoding key| >> |decoding key|?
I'm looking for an encoding scheme that requires a very large encoding key E (>10MB) and suffices with a relatively small decoding key ...
3
votes
3answers
350 views
What is the PRG period of stream ciphers such as RC4 or Salsa20?
I am confused about how long a stream cipher can be used before you should change the key. To be concrete, let me use the stream cipher based on RC4 as an example.
Let's say I want to encrypt a very ...
6
votes
4answers
485 views
Is compressing data prior to encryption necessary to reduce plaintext redundancy?
As explained in William Stallings' Book, in PGP encryption is done after compression, since it reduces redundancy.
I couldn't relate encryption strength with redundancy. Could anyone explain more on ...
0
votes
1answer
116 views
BigInteger in Java and Randomness
I'm looking for some PRNGs and as I have been using Java for a long period of time I thought that the BitInteger class together with the Random class could both generate some large pseudo random ...
2
votes
1answer
78 views
Educational videos for security topics [closed]
Is there anything like the famous "sorting out sorting" video in cryptography/security.
I am looking for some nice videos that explaines SSL, SET, IPSec, PGP, S/MIME ....
5
votes
2answers
651 views
How to calculate an IV when I have a shared private key?
I'm working with a server/client system that has securely negotiated a private key. I need to encrypt/decrypt messages passing in both directions which are typically between 100 bytes to 100 KB. I'm ...
-2
votes
2answers
218 views
Factoring a polynomial over a GF [closed]
I have the following question:
What polynomial, when factored over the field $GF (2^8)$ based on the irreducible polynomial that is used in Rijndael, will factor into all the polynomials in the ...
3
votes
1answer
162 views
Is a subset of a random set still random?
Suppose you have an infinite list of random bytes, and you select the first N bytes that correspond to printable ASCII characters. Is this list of N bytes still as secure (e.g. for the purpose of a ...
4
votes
2answers
213 views
Checking a key before actually using it
I have a block of data crypted using twofish with a key of 128 bit.
The data must be accessed from a GUI, the user gives the key, the block is decoded and the real data is accessed.
Problem is that ...
2
votes
1answer
254 views
How realistic is a dictionary attack on a secure remote password protocol (SRP) verifier?
I'm deploying a secure remote password protocol implementation and I'm wondering what the consequences are when the client generated verifier gets leaked to an attacker. I've read Thomas Wu's paper ...
6
votes
2answers
192 views
Unit testing a library RNG and its seeding for practical security
Suppose I have a cryptography library that provides me with a black-box random number generator that is supposed to be suitable for long-lived key generation. (Under the hood it may be assumed to use ...
1
vote
1answer
102 views
Secure Remote Protocol - Are these 2 equations equivalent?
I'm implementing the Secure Remote Protocol that is specified to have this equation for the parameter S, the premaster secret.
...
4
votes
2answers
357 views
Order Preserving Encryption for Numeric Data Values
How can I ensure order of encrypted data i.e., Enc(m1) < Enc(m2) where m1 < m2, and all messages are integer values.
I have gone through Order Preserving ...
4
votes
4answers
2k views
Does the SHA hash function always generate a fixed length hash?
I'm using the SHA1/2 family of algorithms for a particular project. I'm was wondering if all the SHA algos return a fixed length hash regardless of the length of the data?
2
votes
0answers
110 views
john the ripper, usages [closed]
As evident from the site of john the ripper, JTR example, john can be used for finding password form a unix machine passwd file.
can JtR be used to crack password ...
0
votes
1answer
139 views
Block ordering and security in a MAC?
To authenticate a message $m = m_1 \,\|\, \dots \,\|\,m_n$ the tag $t := F_k(r) \oplus F_k(m_1) \oplus \dotsb \oplus F_k(m_n)$ is used, where r is uniform random number $(0,1)^n$ and $m=(0,1)^n$. Even ...
3
votes
2answers
225 views
Is it generally possible to employ brute force methods when the encryption scheme is not known? Why or why not?
Lets say you are presented with an encrypted string of bits or text, and no other information. What would be necessary before you could apply brute force methods to decrypting the string? How would a ...
4
votes
1answer
107 views
If plaintext is random, how does it affect my choice of encryption algorithm?
I want to encrypt a key file, which is assumed to be truly random (generated with hardware RNG, for instance). Given that there are no patterns in the plaintext, what implications are there for my ...
4
votes
2answers
554 views
128 bit hash with least chance of collision
I'm building a storage system for JSON documents where they are looked up on a 128 bit key. These JSON documents have a timestamp within them, but apart from that are user-entered data. These JSON ...
5
votes
1answer
256 views
How should I check the received ephemeral Diffie-Hellman public keys?
In my application I'm doing a DH key exchange, where both sides generate their
own ephemeral key. No static keys are used. I am trying to make my
application resistant against an active attack and ...
6
votes
2answers
299 views
What are the methods to construct a primitive binary nonlinear feedback shift register (NLFSR)?
Given a binary shift register of $n$ bits, a primitive binary nonlinear feedback shift register will generate a sequence with a period of $2^n - 1$.
While I am unable to find a paper which directly ...
3
votes
3answers
4k views
RSA encryption with private key and decryption with a public key
Does the encryption with a private key and decryption with a public key works in RSA? Is it done when we use RSA for sender authentication ?
Thanks.
2
votes
1answer
92 views
McEliece for streaming data
Under the assumption that there exists a real-world implementation of the McEliece scheme, could it be applied to streaming data as is? By that I mean in 'block cipher mode'? I've read that McEliece ...
4
votes
1answer
192 views
S-box Cryptanalytic Resistance
In DES, different S-boxes were tested for cryptanalytic resistance and the most secure one was chosen for the algorithm itself.
How do different S-boxes offer different levels of security against ...
2
votes
1answer
59 views
Are there any signature schemes that protect against collusion by multiple parties?
Say I want to verify the identity of Alice, but Alice could be colluding with Bob to fool me. Is there any way to verify Alice's identity and also be sure that Bob is not impersonating Alice, e.g. ...
1
vote
1answer
248 views
Is this fixed length MAC unforgeable?
Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$:
On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
4
votes
1answer
185 views
Why does RSA give better security on longer messages?
I am trying to understand the notion of RSA security.
Choosing a public exponent where $e = 3$ facilitates the calculations, considering that it is secure if the plaintext or message is long.
If the ...
7
votes
2answers
242 views
What is the purpose of using different hash functions for the leaves and internals of a hash tree?
I just learned that the THEX hash tree specification which is widely used in P2P requires that two different hash functions be used: one for the leaf nodes (hashes of input data) and one for the ...
4
votes
2answers
187 views
Is SHA1 secure with such many inputs Z that Z = constant secret X + variable public Y?
Let me ask whether SHA1 is designed to be secure for the following case.
You compute each SHA1 of many strings,for example 1 million, where each string is a concatenation of X+Y ,
where X is secret ...
4
votes
1answer
363 views
How is BCrypt secure when it uses a static dataset for blowfish hashing?
I'm planning on using this Javascript BCrypt implementation, but as you can see in the code, it uses a 4KB precalculated dataset for the P and ...
2
votes
1answer
86 views
Is the following scheme secure for different cipher
Let's say I have
two keys K1 and K2.
two messages M1 and M2 of the same length.
Cipher (E,D)
3 ciphertexts: C11, C12,C22 where Cij = E(Ki, Mj)
In situation ...
0
votes
0answers
46 views
Elliptic curve Cryptography [duplicate]
Possible Duplicate:
Can we use elliptic curve cryptography in wireless sensors?
How to map message character to point lies on Elliptic Curve? how to ecc used in wireless sensor networks? ...
1
vote
2answers
437 views
Why do all hash functions use big-endian data?
I've looked at several hash function specifications, and they all emphasize the need for big-endian byte ordering. Is there a reason for this that has to do with security, or is it simply convention?
5
votes
1answer
340 views
How does a “Tiger Tree Hash” handle data whose size isn't a power of two?
Constructing a hash tree is simple enough if the data fits into a number of blocks that is a power of two.
...
2
votes
1answer
284 views
Implementing the BGN Cryptosystem
Question: If you had to implement BGN, how would you do it?
I'm looking for an implementation of the public-key cryptosystem due to Boneh, Goh, and Nissim (aka BGN), or at least some suggestions on ...
6
votes
2answers
1k views
Predicting values from a Linear Congruential Generator
I have learnt that Linear Congruential Random Number Generators are not cryptographically secure - my understanding is that given an LCG of the form:
...
1
vote
2answers
210 views
How to generate successive stream-cipher keys?
I've identified a weakness in a distributed simulation system I'm looking at, and I'm looking for some advice on how to fix it.
Clients initially negotiate an authentication token with a login server ...
4
votes
3answers
393 views
CBC - a canonical mode, even though there are streaming modes
Why is CBC considered the canonical mode when there are streaming modes available such as CFB and OFB? One thing that I can think of is that in CBC you can easliy do range-based decryption. All you ...
3
votes
3answers
375 views
Division in paillier cryptosystem
Is division possible in the Paillier Cryptosystem? i.e. given a the cipher-text $C$ of an integer $M$ the plain-text divisor $D$, and only the public key, can one compute the cipher-text of $M/D$ ?
5
votes
1answer
932 views
Permutations of pseudorandom data
Assuming a bit string is deemed cryptographically secure, e.g. PRNG using AES in counter mode, can we equally assume any permutation of said bit string is also cryptographically secure?
In a more ...
5
votes
1answer
357 views
RSA-OAEP Input Parameters
When creating padding for RSA using OAEP, a message is prepared as follows:
Hash(Input Parameter) || Zeros || 1 || Message
My question is, what should the Input ...
3
votes
2answers
272 views
are CFB and OFB really meant for streaming?
CFB, OFB and other modes are meant for streaming and don't require padding. Are there still limitations such as the text needs to be greater than key length?
2
votes
3answers
202 views
Complexity of arithmetic in a finite field?
I am wondering what the complexities are of adding/subtracting and muliplying/dividing numbers in a finite field $\mathbb{F}_q$. I need it to understand an article I am reading.
Thank you
2
votes
0answers
529 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 ...
