analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)
0
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1answer
169 views
Break double encryption
Let $E_k$ : {0,1}$^l$ be a block cipher encryption function with block-size $l$ and key-length $n$.
In class, we saw that a double encryption with two independent keys $E{}'_{k_1k_2}(x)$ = ...
2
votes
1answer
286 views
Example Rainbow Table Generation
I have read up on rainbow tables and think I understand the idea behind them. However, I find that it would be better for me to actually attempt to implement a (very basic) rainbow table generator in ...
2
votes
2answers
111 views
High Power Computing for Crypto Research
Obviously, much of cryptography requires the assumption that adversaries have bounded computing power.
So, I was wondering, are there any fields in cryptographic research for which high power ...
5
votes
2answers
690 views
Why do block ciphers need a non-linear component (like an S-box)?
Why is there a requirement of "Non-Linear functions" as a component of many popular block ciphers (e.g. the S-box in DES or 3DES)?
How does it make the cipher more secure?
The only intuition I have ...
3
votes
1answer
210 views
Hill cipher, unknown letter value
I've been struggling on this problem for a while now : the Hill cipher is well-known to be vulnerable to known-plaintext attack due to its linearity. Given a key matrix $K$ of size $n\times n$, one ...
4
votes
1answer
153 views
Can a nested block cipher avoid the meet in the middle attack by using a secret initialization vector for the inner encryption?
It seems to be believed that encrypting twice with a block cipher using an independent key each time is not as secure as you might expect because of the "meet in the middle" attack.
This is an attack ...
1
vote
1answer
125 views
Is this attack for RSA possible?
$N=p·q$ ($p$ and $q$ are prime numbers), $m_1, ..., m_x$ are the messages, $e$ and $d$ are RSA encryption and decryption exponents, respectively.
I am given $e, m_1, m_1^e, m_1^d, ..., m_x, m_x^e, ...
2
votes
0answers
60 views
Differential Cryptanalysis of FEAL-4
I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall.
Basically I attacked the final round first (K3) using the differential characteristic of ...
3
votes
1answer
88 views
Why doesn't this replay attack work on ECDSA?
I've just started working with elliptic curves and ECSDA in particular, so my understanding of the underlying math isn't great. The thing I'm currently stuck on is trying to understand why replay ...
3
votes
2answers
202 views
How can I break a Vigenère cipher with partial plain text?
I have an exercise to do regarding Vigenère encryption.
I've got the cipher text: WNZTNVIEEGTJYKRRWYUELWNZTNV
and a partial plain text: ...
3
votes
1answer
244 views
Get RSA PlainText without Knowing Private Key
If I have an algorithm,RSA-Crack(), that, for a given RSA public key (n,e), is able to decrypt 1% of the messages encrypted with that key (without knowledge of the corresponding private key).Can there ...
2
votes
3answers
132 views
Safety of DSA key parameters sharing
I'm looking for a solution to use in a context where I need to be able to generate new asymmetric key pairs quickly (using a widely recognized algorithm, and EC-DSA is not applicable). It sounds like ...
-5
votes
1answer
97 views
My Hand Cipher, Can some one tell if it secure [closed]
In easy steps how it works,
Convert txt to numbers . mod 1-26.
Generate random numbers (By my other cipher) equal to plain txt.
Write random numbers under txt numbers.
txt= LOI - txt number= 12 15 ...
0
votes
0answers
75 views
Actual weakness RSA [closed]
I need modern trends analysis RSA. Hinek books "Cryptanalys RSA and Yan "Cryptanalytic RSA" have been read. What else?
-1
votes
1answer
177 views
detecting ROT13/base64 encryption
Is there anyway to detect that a cipher is encrypted with ROT13 Or Base64 without decrypting it using the algorithm and check that the result means (works)?
I mean does an algorithm exists that test ...
13
votes
4answers
544 views
Is Wiener's attack on RSA extendable to larger keys with low hamming weight?
Using small private exponents with RSA improves performance.
However, it has been shown (Wiener, 1990) that if $\log d \leq \frac14 \log N$, the private exponent $d$ can be reconstructed from the ...
0
votes
2answers
118 views
Breaking RSA, given a special kind of oracle that decrypts related ciphertexts for us
Let $c=E^{RSA}_{e}(w)$ be the ciphertext belonging to the plaintext $w$ if an $RSA$ system is used. Assume that the public exponent $e$ satisfies $e \le 10$. Furthermore, assume there is an oracle ...
4
votes
2answers
202 views
Tunnels used in md5
I'm reading a paper about finding collisions for the MD5 hash algorithm involving the concept of tunnels.
But I couldn't understand about the difference between point of verification and point of ...
1
vote
2answers
265 views
Simply put, what does perfect secrecy means?
I would like to ask for a clear (but maybe not so deep) explanation of what the term "perfect secrecy" means.
As far as I have researched and understood, it has to do with probabilities of assuming ...
-4
votes
1answer
250 views
finding collision for truncated SHA1 hash output
Suppose we truncate only 40 bits of sha1 hash output.hence it is insecure.how can we find two message as input which gives first 40 bits of hash as same value i.e we have to find collision for first ...
1
vote
1answer
156 views
Is there a security analysis of CryptDB?
Its interesting to see critical thinking being applied to cryptDB in contrast to all the hoopla around it here . cryptDB is not a major theoretical breakthrough but potpourri of technologies to make ...
0
votes
0answers
80 views
How to encrypt OpenVPN setup traffic [closed]
I have an OpenVPN server and a client that can successfully connect to said server. The traffic over the tunnel is encrypted. The tunnel works quite well.
However what is NOT encrypted (cleartext) is ...
0
votes
0answers
64 views
Need help with student project about IT security [closed]
I've been studying in university for computer security for 4 years.
All students have to make a course project by the end of year. And I have some problems with it.
I need help with the project's ...
8
votes
2answers
753 views
Can two different pairs of RSA key have the same modulus?
Can $n=pq$ be part of two different pairs of RSA keys?
If such keys exist, say $(e_1,n)$ and $(e_2,n)$, how are they related?
What will be the security concerns for the two users?
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votes
1answer
81 views
What is the complexity of the Square attack against the reduced 4-rounds 128-bit Rijndael variant?
I'm looking at a square attack against a reduced version of AES-128 with only 4 rounds (with block and key size of each 128 bit). I have a set of 256 plaintext-ciphertext block pairs.
What is the ...
19
votes
4answers
2k views
Is AES-256 weaker than 192 and 128 bit versions?
From a paper (via Schenier on Security's Another AES Attack) (emphasis mine):
In the case of AES-128, there is no known attack which is faster than the 2128 complexity of exhaustive search. ...
5
votes
2answers
561 views
Assistance Cracking Classical Cipher
Below is the cipher text I am trying to break and as you can see its rather short which is why I am having so much trouble.
...
4
votes
1answer
296 views
How was the complexity of the Biclique Attack calculated?
The abstract of the Biclique Attack paper claims:
The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$.
What does $2^{126.1}$ mean in this context? And ...
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votes
2answers
224 views
Cryptanalysis of S-DES - Equations
I am trying to derive equations for s and t in the cryptanalysis of a Simple DES algorithm, but I haven't been able to deduce it. I've attached an image of the portion that I'm referring to, and I'd ...
1
vote
1answer
289 views
AES encryption for images [closed]
Why AES based encryption is not recommended for encrypting images with high redundancy in their content? for example, the encryption of an image which shows a bird in the blue sky. Most of the pixels ...
4
votes
2answers
1k views
How does a padding oracle attack work?
I am unsure of how a padding oracle attack works.
What I am not getting is how changing one bit at one time allows one to exploit(get keys) ASP.NET machines.
Can anyone explain this?
1
vote
3answers
217 views
How to encrypt data and know it will be secure for at least a few decades?
I want to encrypt a small amount (few kilobytes) of data and be fairly confident it will be secure against brute force decryption and advances in cryptanalysis for at least a a few decades (or more). ...
7
votes
4answers
1k views
What is the effect of the different AES key lengths?
How does a changing key length affects the ciphertext, not only in case of AES, but in general? I know that the key spaces become much larger and the number of rounds in case of AES changes, but is ...
9
votes
2answers
251 views
Why is the salt used only once in PBKDF2, while the password is used often?
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But ...
0
votes
1answer
313 views
Cryptanalysing Affine cipher
I am trying to cryptanalyse a cipher–text encrypted by Affine cipher.
The encryption formula is: $c = f(x) = (ax+b)\bmod m$, where $a$ and $b$ are unknown constants; $x$ is a plain-text symbol, and ...
2
votes
1answer
109 views
What are the dangers of predictable (repeated) plaintext structures?
When using a "good", modern cipher (specifically one that provides ciphertext indistinguishability), is it a problem at all if there is some well-known structure in all plaintexts?
For example, ...
8
votes
3answers
446 views
What is the best way to put a backdoor in an encryption system?
How can you put a backdoor into an encryption algorithm? Are there any techniques that can be used to reduce the time it takes to break a key?
I am looking for practical examples encryption schemes ...
2
votes
2answers
243 views
Can I build a secure tweakable block cipher from a normal one by adding key and tweak?
Let (E,D) be a secure block cipher.
Consider the following tweakable block cipher:
...
0
votes
1answer
317 views
How to hack the new save encryption on ipad for uplink? [closed]
The new iPad version of Uplink appears to be using some new saving mechanic than the PC/Mac Version. Macs and PCs use 'RedShirt' but the iPad appears to instead be using 'SAV62' at the start of saves, ...
2
votes
2answers
592 views
How can I break REDSHIRT / REDSHIRT2 encryption?
Recently, a user on Gaming.SE asked a question about whether the user password in the video game Uplink could be modified after being initially set. The game does not contain an option to change the ...
1
vote
1answer
167 views
Other than brute force, are there any attacks on Threefish-512 using only a single known plaintext block?
As per title, other than brute force, are there any attacks on Threefish-512 using only a single plaintext block? Are there any attacks like this in any other cipher?
1
vote
1answer
484 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
134 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 ...
1
vote
2answers
934 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
377 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
181 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
484 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
556 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 ...
