1
vote
1answer
98 views

Do per connection random keys solve the stream cipher key repetition issue?

Edits: added then removed additional cases that on reflection seem like a bad idea. In fact, this whole line of thought seems like a complicated way to get a bigger nonce, which might be better ...
1
vote
0answers
161 views

Factoring large numbers

I am trying to factor few integers that are each between 115 and 135 digits long. I have just, little over a month ago, began my study of Cryptography. I was wondering if anyone knew of any efficient ...
6
votes
2answers
1k views

What does it mean if second half of 8-char string encrypted in 3DES is always identical?

In the recent Adobe passwords leak, presumably encrypted in 3DES ECB, second half of all 8-character passwords is identical: ioxG6CatHBw== Source: http://pastebin.com/iDTFARwq (guesses based on ...
0
votes
1answer
167 views

RSA 896 vs 1024 vs 2048 in Javascript?

I am currently working on a secure messaging website and I had been using RSA 2048 for encryption, decryption and signing of messages but I found it to be EXTREMELY LAGGY so i've moved to 1024. I did ...
1
vote
3answers
296 views

Can ECB mode really leak some characters?

In an Ars Technica article about Adobe's use of 3DES in ECB mode, there's a paragraph The passwords, according to password expert Steve "Sc00bz" Thomas, are encrypted in a mode known as ECB. That ...
1
vote
1answer
73 views

secret sharing of product of 2 numbers

Does evaluating the products of shares $a_jb_j$ give a secret sharing of $ab$? I think it's a no, but I am not sure on how to prove it.
0
votes
1answer
77 views

What is the difference between exhaustive search and factorization in relationship to determining a key?

It seems to me an exhaustive search would simply try to use all the possible bit combinations of a key, while factorization is some mathematical formula for determining the key? When discussing the ...
3
votes
1answer
230 views

Are there any Javascript CSPRNGs?

I'm writing some software that requires the use of a CSPRNG with javascript for use in the browser and I'm wondering what libraries are available. Crypto-js doesn't seem to have a CSPRNG I can ...
0
votes
2answers
382 views

HMAC vs Encrypted Hash

What is best to use (for message integrity) between… AES(Data) + HMAC(Data) AES(Data + HMAC(Data)) AES(Data + Hash(Data)) …and why?
4
votes
1answer
113 views

Why does CBC-MAC need prefix-free inputs to be a good PRF?

In the FFX spec, there is a note about using CMAC as the round function. Security notes. The round function F is constructed in such a way that the set of inputs on which the CBC-MAC is ...
3
votes
1answer
192 views

Serpent cipher : Osvik S-Boxes confusion and test vectors

I'm having hard time with the implementation of the S-Boxes by Osvik found in this paper: Speeding up Serpent. At the end of the paper, all the s-boxes are given and then, I just implement them. ...
4
votes
1answer
95 views

Question about the definition of a perfect cipher

I need to prove that the following encryption scheme is a perfect cipher: Let $p$ be a prime. The secret key is a pair $(a,b)$ sampled uniformly at random from $\mathbb{Z}_p^* \times \mathbb{Z}_p$. ...
1
vote
1answer
91 views

Public Key encryption /Assymetric encryption

For a start, I 've got a question regarding the Public key encryption. I know the public key encryption overcomes the Key distribution issue with the symmetric encryption and that in the case of ...
3
votes
1answer
77 views

How would you encrypt-then-MAC when using pen-and-paper and a Caesar cipher?

I'll probably get shot for asking this, but I've got some kids (aged 8-10) in my neighbourhood that I've been showing/teaching the simple pen-and-paper Caesar cipher and they're successfully playing ...
2
votes
1answer
171 views

How is digital signature different from a message authentication code (MAC)?

I know the definitions of both but can't specifically tell how they are different and if one is better than the other. Please help.
0
votes
2answers
189 views

In Elgamal, the generator g is always quadratic non-residue modulo p where p is a safe prime and inverse of g can be also generator?

In Elgamal, the generator $g$ is always quadratic non-residue modulo $p$, where $p$ is a safe prime and the inverse of $g$ can also be generator? Can I prove it? I can't come up with it at all.
0
votes
1answer
51 views

Hash of multiset of values, which lets me compute the hash of the union

Cryptographic hash functions normally take as input a bitstring. I am looking for a hash function that takes as input a finite multiset of values. In other words, given $S \subset \{0,1\}^*$, I want ...
0
votes
1answer
507 views

Does ssl_rsa_with_rc4_128_md5 have known weaknesses?

My bank's website uses HTTPS with the cipher suite ssl_rsa_with_rc4_128_md5. What are the known weaknesses of this suite? Do they have a practical impact for ...
1
vote
3answers
563 views

How to use HMAC-SHA1, HMAC-SHA2 in conjunction with AES

I understand how to compute HMAC-SHA1, HMAC-SHA2 etcetera. Please explain why/how is the resulting HMAC value is used in conjunction with AES for encryption/decryption and signing/verifying. In ...
0
votes
2answers
367 views

If I have the unencrypted text and the encrypted text, can I calculate the key?

If I have the unencrypted text and the encrypted text, can I calculate the key? It seems logical based on my limited knowledge of encryption that I should be able to... but it also seems like too ...
3
votes
1answer
160 views

How to calculate entropy of a combined key

I know how to calculate the entropy of a key that relates to its selection process. For example if the key space is $1000$, entropy of a randomly chosen key is $1000$. Suppose now you have two keys ...
5
votes
2answers
146 views

Cryptanalysis and weaknesses of SEED cipher

I've discovered that a client has SEED enabled in their SSL ciphers, and would like to know a bit more about it from a security perspective. The Wikipedia article doesn't mention any flaws, yet I've ...
1
vote
1answer
267 views

How are IVs used in association with RSA Encryption?

How are IVs used in association with RSA Encryption? Can someone explain why we use them in this RSA context?
2
votes
0answers
69 views

How does use of HMAC affect hash function combiners?

In the comments of this question, Ricky Demer proposes a function $HMAX$ to combine two $HMAC$s based on different hash functions: $HMAX_{H0,H1}(⟨k_0,k_1⟩,m) = HMAC_{H0}(k_0,m) \oplus ...
4
votes
2answers
164 views

How to Distribute the Shares using Secret Sharing for arbitrary Monotone Access Structures

Consider 4 people, $A$,$B$,$C$,$D$, & a secret $s\in\{0,1\}^k$. Construct a scheme which enables the following subsets of people to retrieve the secret $\{A,B\}$, $\{A,C\}$, $\{B,C,D\}$. I know ...
1
vote
1answer
116 views

Feasibility of using a base 26 LFSR for cryptography by hand

I have been playing with base 26 LFSRs (i.e. using the alphabet) and noticed that the XOR operation for base 26 is just the tabula recta and so can be done very quickly. This made me wonder whether a ...
3
votes
2answers
381 views

Attacking 2DES efficiently

Meet in the middle on 2DES uses $2^{56}$ memory. Given the fact that the attacker has only $2^{45}$ memory. How can the attacker adjust the attack so even with this memory limit, it will still be more ...
1
vote
0answers
112 views

How to develop a public key cryptosystem based on a hard problem?

Recently, I found a function that is performed on a sequence to return another sequence. All known algorithms for finding the input, given the output are of exponential complexity. I want to propose ...
1
vote
0answers
45 views

Can you help me understand this strange implication direction in security reduction for OAEP 3-round?

I'm reading the paper OAEP 3-round, where they introduce a 3-round version of the OAEP (which originally used only two rounds). However, in their security statement for this construction (Theorem 4 ...
7
votes
1answer
191 views

Are there any differences in operation between existing Diffie-Hellman specifications?

Are there any differences in operation between existing Diffie-Hellman specifications, especially those within the RSA PKCS#3, ANSI X9.42 and RFC 2631 standards?
0
votes
1answer
165 views

Why is the hashing (SHA256) specification symbol for rotate S and vice versa? [closed]

In the specification for SHA hashes, such as SHA-256, the symbol for a rotation is S and the symbol for a shift is R. Is this an attempt to be deliberately confusing, or some kind of in joke, or ...
2
votes
0answers
81 views

Why does the new encryption scheme proposed by authors stop an adversary from guessing the subspace of the secret key?

In this paper, the authors construct an encryption scheme that is supposed to be resilient to tampering and leaking (as opposed to just leaking). Specifically this scheme: If you look at the ...
2
votes
1answer
160 views

How does the IV or initial counter increase internally for each block in AES CTR mode?

I am working on Intel AES-NI library and since the AES function is coded using low-level assembly instructions. I could not see how the IV or initial counter increases in CTR mode. In general, how ...
0
votes
1answer
62 views

Why do authors say conflicting things regarding leak-free stages in their paper?

In this paper the last sentence of the first paragraph in the abstract states: We assume a (necessary) “leak-free” preprocessing stage. But then later on in section 1.4 they say Another ...
1
vote
1answer
189 views

XOR secret sharing scheme

I was wondering how we can get a secret sharing of $a+b$ from the sharing of secrets $a$ and $b$ themselves by using an XOR secret sharing scheme, where $a_1,...,a_n$ and $b_1,...,b_n$ are the shares ...
2
votes
0answers
58 views

Any functioning system for interactive proof?

My problem is to outsource an array of data and ask the prover to sort the data. I am wonder if there is any working system out there that support interactive proof for the above computation? Or if ...
2
votes
1answer
266 views

How good is using AES CTR mode with initial counter as 0?

Is it advisable to use AES CTR mode with the counter initialized to 0? How good is it in security terms?
3
votes
1answer
147 views

Why is a simple hash into $G_2$ for (certain) pairing based crypto not possible?

In the paper Pairings for Cryptographers we read about what the authors call a type 2 pairing in which we have a "pairing friendly curve $E$ over $\mathbb{F}_q$ with embedding degree $k>1$ and ...
1
vote
1answer
89 views

Are there any practical examples of breaking a system using linear attacks?

I've read some papers about linear cryptanalysis. But since I am going to give a lecture about it I am looking for an example of breaking a system using this attack. Is there such an example ...
3
votes
0answers
77 views

Hi Sec National algorithm

I'm trying to create a remote controller compatible with HiSec algorithm. It's so old that National (now Texas Instruments) discontinued NM95HS01/02 and docs are unavailable. Does anyone have the ...
1
vote
1answer
78 views

Distinguishing joint probability distributions

Assume that we have a probability distribution $P(X,Y)$ for the joint probability of random variables $X$ and $Y$. Let $P(Y, Z)$ be analogous distribution for $Z$ and $Y$. Based on these we can define ...
7
votes
1answer
309 views

Why are the initial states of hashes functions (like SHA-1) often non-zero?

There is already a question asking "Why initialize SHA1 with specific buffer?" and my question follows on from this: Why are the initial states of hash functions often non-zero? For most, I have ...
0
votes
1answer
241 views

openSSL ECDH private key size

When you are using a named curve like P-256 in openSSL, is there any standard key size for ECDH private key keys? If you look at the ec_key.c file in the openSSL ...
3
votes
2answers
215 views

Definition of a CSPRNG

I am interested in what conditions are necessary and sufficient to define a cryptographically secure pseudo-random number generator (CSPRNG). Wikipedia lists two defining characteristics: It ...
1
vote
1answer
472 views

Are there any Truth Table to Boolean expression converters? [closed]

I am working on Bent functions that are of interest in cryptography. I developed an algorithm that construct such functions. However, I need some tools to calculate boolean expression from the truth ...
2
votes
1answer
110 views

Why does Merkle's Puzzle requires Eve quadratic complexity of effort to break the system?

The way Applied cryptography 2ED explains the puzzle is as follows (I paraphrase it): Bob generates 2^20 messages of the form x,y where ...
2
votes
1answer
102 views

What is the limit of plaintext required to break the Vigenère encryption?

A theoretical question about the Vigenère cipher: Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely ...
2
votes
1answer
98 views

How does SSL secure the initial handshake?

I'm reading the SSL specs, and it seems that the initial handshake has no authenticity protection at all. What is to prevent, say, an attacker from overwriting the "available ciphers" list with one ...
1
vote
1answer
148 views

What's the difference between the long term key and the session keys?

I'm currently studying secret key cryptography, and I've come across the terms "long-term key" and "session key". What's the difference between these two kinds of keys?
1
vote
2answers
147 views

Are there attacks that break collision resistance but not preimage resistance?

Are there any examples of attacks on hash functions which: break collision resistance and second preimage resistant, or break collision resistance and preimage resistant? I have looked at ...

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