Analysis of individual security aspects of a cipher or algorithm, not the security of a cipher or algorithm in general (which would lean towards “algorithm-design”).

learn more… | top users | synonyms (1)

1
vote
0answers
16 views

How to calculate LOW(b) and HIGH(b) in spritz cryptography

I try to implement spritz cryptography like this paper . But I don't know how to calculate LOW(b) and HIGH(b). In paper page 7. ...
2
votes
1answer
187 views

Finding key of AES in ECB mode

How many plaintext-ciphertext pairs would be needed to guess with probability, say $p=0.5$, the key $k$ of AES under ECB mode? Most of the articles that I found tried attacks on single plaintext-...
7
votes
2answers
439 views

Developing algorithm for detecting plain text via frequency analysis

First post on Crypto SE, so I've attempted to search the term "English" and looked through the first 10 pages of results, to see if this was a common question, I couldn't find a suitable answer. I'm ...
2
votes
0answers
55 views

how to decrypt hidden text under numbers? [closed]

got a question as follows - how to decrypt below in to letters knowing that crypting language is 469 and it base ofcourse on mathematic. 46781! 9063376290 3222011 677 80322429 67538 14805394, 6880326 ...
-2
votes
1answer
66 views

How do we solve Shammir 2,3 sharring scheme where arithmetic is modulo?

I am trying to get secret S and I have 3 values (2,2)(6,3)(4,9) and know that modulo is 13. I tried using Lagrange basis polynomial and got 8 but I am not sure if that is right and also I cannot find ...
2
votes
3answers
94 views

Find plaintext from two ciphers encrypted with a one-time pad and the same key

I'm studying for a cryptography test and I came across this question: Assume a language has three letters: A=1111, B=0011 and C=1010. Two words in this language are encrypted with a one-time pad ...
6
votes
2answers
245 views

Can Grover's Algorithm be combined with a meet-in-the-middle attack?

We all know and love the meet-in-the-middle attack which basically makes double encryption pointless using a time-memory-tradeoff. Now there was recently the recommendation by the NSA to use double ...
2
votes
1answer
52 views

What is the most an adversary can do in the context of public key masquerading?

Suppose two parties A and B are using a public-key encryption scheme in order to communicate securely. A and B both have a public/private key pair: $$ A: (P_A, S_A), B: (P_B, S_B)$$ and A already ...
2
votes
3answers
202 views

One Time Pads and reuse of the decrypted message?

How is it insecure when Alice encrypts a message with a One-Time-Pad to Bob, and Bob then uses the decrypted message from Alice as the next One-Time-Pad? For example: Alice sends Bob a message ...
1
vote
0answers
82 views

Carrying out a known-plaintext attack on a cipher [closed]

Previously posted here. Someone suggested I could post it here to get some answers. I am trying to solve a CTF challenge, here. Basically we're given message and key inputs to a cipher and its ...
2
votes
1answer
82 views

Output of using the same key in all 3 boxes of 3DES

I am trying to figure this one out: What would be the encrypted output for an input x if the same key K is used in all three boxes of 3DES? The encryption scheme for 3DES with three different keys, ...
3
votes
0answers
75 views

How to overcome issues with big ciphers? E.g. with small vs. big Vigenére Ciphers

I understand that bigger ciphers show more recurring patterns and therefore should be easier (or at least faster) to decrypt as you'll have a better statistical analysis, being However if we use a ...
3
votes
2answers
238 views

Memory-hard proof-of-work: are they ASIC-resistant?

Is a memory-hard proof-of-work scheme necessarily resistant to speedups from custom ASICS? Background: Bitcoin uses a proof-of-work scheme based on SHA256 hashing. The scheme is compute-bound. ...
2
votes
1answer
40 views

Data Switching and Information Leakage

Hypothesis: Let $z,a$ be uniformly random elements of a field $\mathbb{F}_p$ where $p$ is a large prime number. Also, let $(-z)$ be additive inverse of $z$. I have a fixed secret value $x$. I mask ...
3
votes
1answer
344 views

Deciphering “easy” ciphers without hints

I've been keen on IT Security for a long time now and I've learned a lot about networking & security. However trying a "decryption challenge" I'm lacking what I think is basic encryption/...
3
votes
1answer
176 views

How to clock a linear feedback shift register?

I have some trouble understanding what happens when a LFSR is clocked. I have tried many examples but I do not get the correct result. Can anyone point out my errors? I have the following polynomial: ...
3
votes
1answer
100 views

Is there any benefit of changing the AES-CCM encryption key periodically even if the Nonce space is not exhausted yet?

I would like an answer that could be sustained by a mathematical proof. Let's say I'm using AES-CCM to encrypt a lot of messages, and I always use a different nonce. I know that when the nonce space ...
4
votes
2answers
114 views

Weakness of SRP after server compromise

From SRP section 3: The host stores user passwords as triplets of the form { <username>, <password verifier>, <salt> } Password entries ...
2
votes
1answer
62 views

Weaknesses of RFC6628

In RFC6628 section 2.2, they say: w = The password remembered by the user. W = The password verifier registered in the ...
6
votes
1answer
280 views

Is it possible to find a Mersenne Twister seed given only the first output?

Suppose I have a Mersenne Twister seeded with some unknown value, and I’ve been given the first output. Given only this first output, and no other information, is it possible to derive the unknown ...
3
votes
1answer
144 views

Avalanche effect sample size

With a fixed key size – key has 128 bits, while block size is 8 byte – how do I calculate how many different keys and texts I have to test for an cryptanalytic statistics study? Differently worded: ...
2
votes
3answers
204 views

Hypothetical encryption technique, is it secure?

This to me, sounds like a great idea, but with all rosy-tinted ideas it needs some grounding in reality. Here are the steps of the hypothetical system (with the hypothetical part highlighted): User ...
40
votes
1answer
4k views

What is a “freestart collision”?

In their work on SHA-1 collisions (cf. the EUROCRYPT-2016 paper “Freestart collision on full SHA-1” by Stevens, Karpman, and Peyrin) Stevens et al show that they are able to generate "freestart ...
2
votes
2answers
70 views

Profile Complexity LFSR

I try to understand how Complexity of an LSFR calculated. For example I have a bit sequence 110101 and it's profile 1 1 2 2 3 3. Is there any easy way in order to produce the profile?
5
votes
0answers
326 views

How to break a columnar transposition cipher?

I'm currently studying for a cryptography exam. I've been given ciphertext that has been encrypted by a columnar transposition cipher. I've been given no shift key length or key word, the only thing I ...
2
votes
0answers
21 views

Does the length of the keyword used for keytable for Playfair matter?

So for Playfair, we choose a keyword and put that in the keytable with no duplicates. Then, we fill the rest of the table with alphabets in order that are not in the keyword without 'J'. Does the ...
2
votes
1answer
108 views

What is the difference between CPA and IND-CPA?

I am writing a paper and I got comments from the reviewer that I don’t really understand. Is there any difference between a CPA (Chosen Plaintext Attack) and IND-CPA (Indistinguishability under ...
8
votes
1answer
279 views

Quantum on hash

Perhaps this has been answered before. Grover's algorithm should result in a 256 bit hash being complexity 128 bits to crack. I was wondering, what if you had a 512 bit hash , and xor'd the lower 256 ...
1
vote
0answers
70 views

Powerline password conversion [closed]

I read this post from Ben Tasker describing how to take control of a powerline network. Since I am interested in security, I tried to do the same thing, to see if it was possible. I used Devolo ...
3
votes
1answer
130 views

RSA: special parameters construction

I have to show that the following construction of $q$ allows to factorize $N$ : $p \in \mathbb{P}$, the set of primes $q \gets p \cdot \left((p - 1)^{-1} \bmod e\right) \bmod e$ $k=1$ while $q \not \...
1
vote
1answer
219 views

Shared modulus attack on RSA

Consider a scenario in which a group of people use a common modulus $n$ in the textbook RSA crypto system, where $n=pq$, $p$ and $q$ are large distinct prime numbers. Is there any chance for an ...
5
votes
2answers
73 views

Does $(u_1=r_1\cdot x,\ \ w_1=r_1\cdot z, \ \ u_2=r_2\cdot x,\ \ w_2=r_2\cdot z)$ Leak Information?

Consider we have a fixed value $x$. We pick values $ r_1,r_2,z\leftarrow \mathbb{F}_p$, where $p$ is a large prime number, and it is public. So $r_1,r_2,z$ are uniformly random values. We compute ...
1
vote
1answer
141 views

How to prove that the Permutation cipher is not CPA secure?

Encryption scheme is called a permutation cipher if every plaintext string with letters $a_1,\ldots, a_n$ is encrypted as $a_{\pi(1)}, \ldots, a_{\pi(n)}$ for some (not necessarily uniform) ...
2
votes
2answers
46 views

(Uniformly) Random Value when an element is picked with $\frac{1}{p-1}- \frac{1}{(p-1)^2}\ $ probability

Let's $\mathbb{F}_p$ be a finite field where $p$ is a large prime number(e.g. 256-bit) I know if the probability that an element picked from the field is $\frac{1}{p-1}$ we say the element is picked ...
-1
votes
1answer
85 views

How To prove Any Change to $v=a\cdot y+b$ maks $y=(a)^{−1}\cdot (v−b)$ Uni. random value [closed]

This question is related to data integrity. Let a finite field be $\mathbb{F}_p$, where $p$ is a prime number. I have a fixed value $y$ and two uniformly random values $a$ and $b$. Hypothesis: $a,...
3
votes
1answer
56 views

Do $v_1=\alpha\cdot r_1$ and $v_2=\alpha\cdot r_2$ leak information about $\alpha$

Please consider we have finite field $\mathbb{F}_p$ for large prime number $p$. We have a fixed field element $\alpha$. By $r_i\leftarrow \mathbb{F}_p$ we mean we pick $r_i$ uniformly random from the ...
2
votes
3answers
165 views

How much processing power should you assume an attacker has?

The answer to this question says that you should assume an attacker can do one billion operations per second: Key Size for Symmetric Homomorphic Encryption Over the Integers Is that a single attacker ...
4
votes
1answer
43 views

Given occasional LFSR samples can the next sample be computed?

Suppose I have access to an LFSR generator output used in a radio communications system, with the LFSR being used to authenticate devices. The system cycles an internal unknown length LFSR (greater ...
0
votes
1answer
99 views

How secure is this modified Bazeries Cylinder?

This device is a modification of the Bazeries cylinder, it has two stacks of 5 rotors which each bear two alphabets plus numbers 0-9, one in correct order and one in random order ( 36 characters in ...
11
votes
1answer
547 views

Does Curve25519 only provide 112 bit security?

In a recent mail on the IETF CFRG mailing list it was claimed that: The (currently missing) security considerations (or somewhere) should describe why Curve25519 is ok when used in contexts where ...
4
votes
4answers
144 views

Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?

Imagine we have $t-1$ shares in $(t,n)$ shamir secret sharing. So at least $t$ shares are needed. Question: Why cannot we use $t-1$ shares to find a root of the polynomial and then recover the ...
-2
votes
1answer
227 views

Having plaintext and ciphertext, how can I learn more about key/encryption?

I have an OLD work database that seems to have a simple encryption on the PW. I have one users whose pw is 7777 the cipher text is ...
1
vote
1answer
365 views

Knowing pre-encryption data, can we find the private key CryptoWall used?

I'm just repurposing a question already asked about Cryptolocker for CryptoWall: "If we know exact contents of some of the files prior to them being encrypted, would it be feasible to use those ...
0
votes
0answers
37 views

Is double encryption using AES using different key lengths (128 bit and then 256 bit) vulnerable? [duplicate]

I know that AES 256 bit is far more than enough to secure a file. I just want to know if there are any vulnerabilities or known attacks which can make such this combination less secure "double ...
3
votes
2answers
147 views

Combine two sha512 hashes to a single hash

Assume I have two data fragments: $Frag_1$ and $Frag_2$. I can build sha512 hashes the usual way with $SHA512(Frag_1)$ and $SHA512(Frag_2)$ and then hash the two fragments appended to each other: $$...
2
votes
0answers
42 views

Is it possible to generate backdoored DH parameters?

I know it has been already asked and answered whether it's possible to generate weak DH parameters. But "recentely" we experienced the Logjam attack, which makes use of the pre-computation ...
4
votes
1answer
157 views

Hashing a Diffie-Hellman result

In many implementations, the result of the Diffie-Hellman algorithm is hashed. I read that: Hashing the shared secret point prevents an attacker from gaining more information about the EC private ...
5
votes
1answer
404 views

Small subgroup confinement attack on Diffie-Hellman

I am trying to understand the small subgroup confinement attack on the Diffie-Hellman algorithm. I will present the attack and try to explain why it works. Small subgroup confinement attack on the ...
6
votes
1answer
182 views

Can it ever be impossible to invert a PRNG?

I've read about the possibility of inverting the Mersenne Twister after 624 numbers of output. 624 matches the state size of my implementation of the Twister. Coincidence? If the generator only ...
0
votes
0answers
33 views

how many pairs of plaintext-ciphertext are needed before we break AES? [duplicate]

Imagine a set of words ($plaintext$) each are encrypted using AES-ECB mode and due to some leakage in the system an attacker could gain access to some pairs of $plaintext$ and $ciphertext$. But once ...