analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)
1
vote
1answer
534 views
Deciphering a key from XOR encrypted cypher using boolean logic
Assume there's an unencrypted message A, and an encrypted message B. You know that message B was encrypted using a simple XOR method of A with a private key K, resulting in message B. Thus,
B = A ⊕ K
...
2
votes
2answers
138 views
Is there a way to compare the 923 bit pairing based key with RSA or AES, etc
I've see many articles, most of them basically the same, praising Fujitsu for cracking what is referred to as a 923 bit pairing based encryption. I understand that in comparing RSA to AES you've got ...
2
votes
2answers
1k views
How much computing resource is required to brute-force RSA?
It's been over 30 years since Rivest, Shamir and Adleman first publicly described their algorithm for public-key cryptography; and the intelligence community is thought to have known about it for ...
7
votes
1answer
3k views
How does the index of coincidence work in the Kasiki test?
I'm starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. I have a book (Cryptography Theory And Practice by Douglas Stinson) ...
13
votes
1answer
403 views
Is this password migration strategy secure?
I want to upgrade the security of some existing databases of users' authentication tokens strictly for the purpose of making sure that if the database is stolen, attackers will not be able to guess ...
8
votes
3answers
2k views
What is the difference between known-plaintext attack and chosen-plaintext attack?
I am very confused between the concept of known-plaintext attack and chosen-plaintext attack. It seems to me that these two are the same thing, but it definitely is not.
Can anyone explain to me how ...
2
votes
1answer
183 views
Regarding matsui's Paper on Linear Cryptanalysis of DES
I's going throught the the Paper by Matsui on Linear Cryptanalysis of DES . In that he says
$NS_{5}(16,15)=12$
And then in the next paragraph he says considering the expansion and permutation phases ...
6
votes
4answers
511 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 ...
8
votes
1answer
587 views
Duration for attacking Two-Key Triple-DES Encryption using all RAM ever built?
I am considering attacks on Two-Key Triple-DES Encryption assuming $2^{32}$ known plaintext/ciphertext pairs (that's a mere 32 Giga Bytes of ciphertext) by the method devised by Paul C. van Oorschot ...
4
votes
1answer
147 views
Where can i find relative software for differential cryptanalysis?
Is there any publicly known software for differential cryptanalysis over some cryptographic building blocks as blocks ciphers or cryptographic hash functions
1
vote
2answers
158 views
How hard is to find the operators of an addition knowing the sum of them?
I want to learn whether or no there is a cryptographic primitive,scheme assumption that is based on the following hard problem if it is hard . By hard we mean that we have a polynomial adversary: The ...
2
votes
2answers
315 views
How to get the keyword from a keyword cipher?
I was given a ciphertext and now I am trying to break it via looking for the keyword.
This is a keyword cipher. So:
PlainEnglish: ABCDEFGHIJKLMNOPQRSTUVWXYZ
If ...
6
votes
2answers
251 views
Attacks of the MAC construction $\mathcal{H}(m||k)$ for common hashes $\mathcal{H}$?
Consider a common practically-collision-resistant Merkle–Damgård hash function $\mathcal{H}$ (e.g. SHA-1, RIPEMD-160, SHA-256, SHA-512). We define a Message Authentication Code $\mathcal{C}$
$$(k,m) ...
1
vote
2answers
167 views
Brute force a ciphered message?
I wrote my own cipher to encrypt messages. I would like to test a sample ciphered message to see how strong it is. Are there any tools for such task either in Windows or Linux ?
3
votes
1answer
327 views
Does the Biclique attack on AES pose a credible risk to its security?
I have heard a lot about the biclique cryptanalysis research on AES, which as far as I know is the closest anyone has got to breaking AES.
Exactly how close did they get? Does this attack propose a ...
3
votes
2answers
501 views
Difficulty of breaking RSA for a given key size
Is it true that breaking a 1024-bit RSA key is as difficult as breaking a 128 bit symmetric key (e.g. AES)? I know that breaking a RSA key is equivalent to factoring the modulus $N$. To factor it, you ...
0
votes
1answer
110 views
amateur cryptosystem -> a very long boolean expression -> attempt to reduce it [closed]
(newbie here) I try to analyze amateur cryptosystem and wondering, if it's possible to reduce it as reduce a very long boolean expression? What tool can I try to use?
3
votes
1answer
217 views
Is XOR in a CBC-like mode secure?
Assuming that $K_{n}$, $P_{n}$, and $C_{n}$ are individual bytes of the key, plaintext, and ciphertext respectively.
The first byte of ciphertext is computed like this:
$C_{1} = K_{1} \oplus P_{1}$
...
1
vote
2answers
174 views
How do I demonstrate that a PRNG not designed for cryptography is not suitable for generating passwords?
This is a replication of this question on Stack Overflow. There's class Random in .NET runtime which is designed for use as a cheap fast source of pseudo-random ...
6
votes
1answer
127 views
Message space in security definitions
What is the message space in the following example and how does a message space relate to a security definition?
I mean, what difference does it make to such a definition if your message space is ...
3
votes
2answers
511 views
What is the smallest plaintext/ciphertext size for an algorithm like?
When I read about a choosen plaintext attack, for example on AES the block size is always 128 bits, does it mean the attacker will only supply 128 bits data words as "plain text" ?
3
votes
1answer
168 views
Has there been any cryptanalysis of RC4-52?
Several websites ( such as Is there a secure cryptosystem that can be performed mentally? ) briefly mention RC4-52 as a modification of standard RC4.
RC4-52 has only with 52 instead of 256 elements ...
-4
votes
2answers
147 views
Any techniques for evading frequency based crypt analysis without encrypting?
Are there any general techniques for evading frequency based crypt analysis without using any encrypting techniques
3
votes
3answers
175 views
Are asymptotic lower bounds relevant to cryptography?
An asymptotic lower bound such as exponential-hardness is generally thought to imply that a problem is "inherently difficult". Encryption that is "inherently difficult" to break is thought to be ...
2
votes
2answers
738 views
How can I do a brute force (ciphertext only) attack on an CBC-encrypted message?
Given a CBC ciphertext and IV, how can I find the encryption key?
We are limited with an 8 chars key, each char in the range of [a..h], so I can generate every possible key (these are only $8^8 = ...
5
votes
1answer
356 views
Would RSA-encrypting a private key for itself constitute a vulnerability?
I'm planning to encrypt some individual files for storage, using the GnuPG implementation of RSA. If I happened to encrypt the private key corresponding to the public key used for encrypting -- either ...
1
vote
0answers
101 views
Security of stream cipher based on Matrix multiplication GF(256) with randomized padding
The actual question is stated at the end of the text. Suppose you have a (grossly inefficient) confidentiality stream cipher with the following components:
The keyed function ...
2
votes
2answers
2k views
How does a chosen plaintext attack on RSA work?
How can one run a chosen plaintext attack on RSA?
If I can send some plaintexts and get the ciphertexts, how can I find a relation between them which helps me to crack another ciphertext?
0
votes
2answers
143 views
CPA distinguisher for matrix multiplication in GF(256) with randomized padding
What is the best CPA distinguisher for the function $F_k:\{0,1\}^{8n}\to\{0,1\}^{16n}$ described below?
Let $E_k$ be a $2n\times2n$ matrix with elements in $GF(2^8)$, selected by generating bit ...
4
votes
2answers
253 views
Predicting PRNG given some of its previous output
I a have a question about PRNGs and this is my very first experience with them. I have the following generator that takes a 56-bit seed 'p' during initialization and then chooses both X and Y randomly ...
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:
...
9
votes
3answers
472 views
Can I use a one time pad key twice with random plaintext?
I understand the basics of OTP: $|\text{key space}| = |\text{plaintext space}|$ implies perfect security, key reuse destroys this.
Cryptanalysis on the $N$-Time Pad for $N > 1$ involves finding ...
2
votes
2answers
347 views
ECC algorithm pollard's $\rho$ complexity
One of the methods to break a ECDLP is Pollard's rho algorithm. When ECDLP is defined over a finite field $F_p$, and given a relation $S=w.T$, where S and T are a member of $F_p$. Then ECDLP is to ...
4
votes
1answer
193 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 ...
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? ...
5
votes
0answers
417 views
What are the popular crypt analysis tools? [closed]
What are the popular crypt analysis tools out there ? for something like Cipher Text only attacks or any attacks in general which does frequency analysis et all
1
vote
0answers
179 views
Deciphering a Message [closed]
I have this message to decipher:
UYDVKUYEHJNRFRLYZIPVSUQYGAFFBXKAJLVRIETJIUOTSVKXHQZUWYLIOQHQEJR
I have tried using methods such as:
Ceaser cipher, Atbash cipher, Railfence etc.
I also tried ...
3
votes
1answer
184 views
Security analysis of a matrix multiplication protocol
Suppose Alice would like to obtain the product of two mXm matrices i.e. A and B. Alice has A, whereas Bob has B.
Since Alice does not want to reveal A to Bob, she chooses a mXm random invertable ...
3
votes
2answers
885 views
Brute forcing CRC-32
I'm working on a cryptosystem which uses IDEA. The designer made the mistake of including a CRC-32B hash of the password unencrypted in the header, so that the system can quickly reject bad ...
5
votes
3answers
576 views
Understanding CRC
There are zillions of articles describing CRC. What can I ready to understand more deeply what's really going on? Both from an algebraic perspective and a bit-manipulation perspective, I'd like to ...
1
vote
1answer
213 views
Security analysis of a “one-time pad” type hill cipher
Suppose the Hill cipher were modified to something like a one-time pad cipher, where Alice wants to send a message to Bob, and she chooses a key matrix randomly everytime a new message is sent (and ...
5
votes
2answers
2k views
Rijndael vs. Serpent vs. Twofish: General comparison
Can anyone explain (or give a link to document about) why Rijndaal won the AES, especially comparing it to other finalists (Serpent and Twofish)? What criteria were used to make decision?
Or is there ...
6
votes
1answer
302 views
Exposing RSA private-key data… bad?
We know that exposing $p$, or $q$ or $\phi(n)$ results in trivial attacks on RSA since they allow us to factor $n$ and to compute the private exponent $d$.
In OpenSSL (and most RSA implementations) ...
0
votes
0answers
109 views
What will be the way to go about deciphering this kind of cipher? [closed]
I've come across this cipher and have tried unsuccesfully to decipher it.
http://codepad.org/aea7Wuyl
The only 'hint' that I have gotten so far as to how I am supposed to crack it is the word ...
7
votes
2answers
419 views
How does the MOV attack work?
What exactly is the MOV attack, how does it actually work, and what is it used for?
It's explained briefly here and I'd like to know what it is more / what is it fully used for.
13
votes
2answers
2k views
Why does nobody use (or break) the Camellia Cipher?
If Camellia is of equivalent security and speed to AES, concerns arise.
First of all, assuming the above, why is Camellia so rarely used in practice?
Why aren't there any breaks in Camellia? Does ...
6
votes
3answers
2k views
Encryption/ciphers/codes in Chinese
I am quite curious as to how you can perform simple encryption for the Chinese language.
Saw a similar question related to encryption/Chinese here: About cryptography in a character language, ...
3
votes
1answer
272 views
Differential cryptanalysis - breaking the last round of FEAL4?
I've been trying to learn cryptanalysis. I've come across this resource which proved very helpful:
http://theamazingking.com/crypto-feal.php
So far I've been almost successful in breaking FEAL4 ...
3
votes
3answers
615 views
A simple block cipher based on the SHA-256 hash function
I've come up with this little routine for doing encryption using the SHA-2 (in this case SHA-256) hash function. As such it is a block cipher with a 256 bit (32 byte) block size and an arbitrary key ...
4
votes
1answer
517 views
Known Plaintext attack against XTEA?
I'm looking for information on known-plaintext attacks against XTEA. I'm most interested in the worst case scenario: if an attacker has all 8 bytes of input and all 8 bytes of output, how much ...
