5
votes
2answers
183 views

power consumption in a XOR

I'm trying to understand how a XOR affect traces of power consumption in a Differential Power Analysis on smartcards. What's the difference in energy radiated in a $1 \oplus 1$ and in a $0 \oplus 1$? ...
4
votes
2answers
1k views

Is there something wrong with my decryption using key=9, mod 26?

I am new to cryptography and have started looking at some basic encryption. I have the following question to answer: Decrypt the the following encrypted quotation using ...
4
votes
4answers
444 views

Where does the $\varphi(n)$ part of RSA come from?

$e d \equiv 1 \pmod{\varphi(n)}$ Where does the $\varphi(n)$ part come from? How did the inventors of RSA arrive at $\varphi(n)$?
4
votes
6answers
2k views

Why does ROT13 provide no cryptographic security?

I can understand that ROT13 is not secure for obvious reasons, but I'm looking for the theoretical answer. Wikipedia says "The algorithm provides no cryptographic security.." What does it mean to ...
4
votes
3answers
856 views

Is there any area where AES-CBC cannot be used ? If so, why?

I would like to know the domains or specific applications where using AES-CBC is not advised due to any drawbacks like sequential encryption of AES-CBC ?
4
votes
4answers
559 views

Why $n=pq$ with $p=2p'+1$ and $q=2q'+1$ instead of just $n=p'q'$ for RSA crypto?

For RSA cryptography, we know that the modulo $n$ is a product of two big prime numbers(say $p$ and $q$). However, in some documents I see an extension of $p=2p'+1$ and $q=2q'+1$ with $q'$ and $p'$ ...
4
votes
4answers
703 views

Why isn't the alternating step generator used more often?

According to the Wikipedia entry for the Alternating Step pseudorandom number generator, there is no public cryptanalysis for this device since it was invented back in 1987 by C.G. Gunther. I have ...
4
votes
1answer
597 views

Why does “2xAES-256” provide “99.99%” security strength whereas “1xAES-128” provides “40%”? [closed]

I recently was "directed" to FlipsCloud, a company selling security solutions (as far as I can tell). In particular I've investigated their page and found a page on their "encryption features". This ...
4
votes
7answers
786 views

A block cipher with independent keys for each round

I want to modify a standard block cipher in the following way. I replace each round key by a key picked at random. Is this block cipher as secure as the original one ? Thank you. EDIT Some missing ...
4
votes
4answers
1k views

What is an efficient random number generation algorithm

I have been looking for the algorithm that generates random number and this algorithm has to be more secure. I am going to use this algorithm to generate the salt that will be used in PBKDF2. ...
4
votes
4answers
551 views

Is there a way to generate sound one-time pads out of public information?

Is there a way to 'mangle' a public data-source (for example, the current date in YYYYMMDD or the top New York Times headline) to form a one-time pad that will sufficiently hide the pad's source? ...
4
votes
4answers
1k views

Increased CRC collision probability when adding bits to input message

The Scenario I have a message string I need to transport over a wireless network that may be unreliable. This message string is about 100 bits long, and is packaged with an 8-bit CRC. When the ...
4
votes
3answers
623 views

RSA primes vs. largest known primes

In the context of a new largest (mersenne) prime number being found this week - The largest known prime number is now 2^57,885,161 − 1, and it took 5 years to find ...
4
votes
3answers
570 views

Block cipher fixed points (plaintext equal to ciphertext)

A block cipher is a bijective map from the set of possible plaintexts to the set of ciphertexts, which are the same size and might as well be considered the same thing: $\theta: S\to S$. In this there ...
4
votes
2answers
410 views

Is it safe to store initial counter value for AES-CTR alongside with ciphertext?

The initial counter value can actually be thought of as a sort of IV, which I assume is safe to transmit with the ciphertext, but I really want to be sure that this is indeed safe.
4
votes
4answers
136 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 ...
4
votes
2answers
11k views

Why we can't implement AES 512 key size?

Out of curiosity why we can't implement AES 512 key size? Please explain somehow i can understand! I'm not an expert.
4
votes
2answers
654 views

Is ECB mode secure if plaintexts guaranteed to be unique?

I've got a scenario where I need to encrypt many small (16-byte) plaintexts. I want to use AES-128 in ECB mode. Notably, each plaintext is guaranteed to be unique, though each may differ by only a few ...
4
votes
4answers
393 views

Is there a secret sharing scheme which allows delegation/re-sharing without reconstructing the original secret?

EDIT: Ilmari Karonen's answer below well not exactly what I want, gives a very good idea of what I am trying to accomplish. Are there any known secret sharing schemes that allow new parties to be ...
4
votes
3answers
3k views

Calculating the amount of zero bits to be appended to the message

From FIPS 180-3 Suppose that the length of the message, M, is l bits. Append the bit “1” to the end of the message, followed ...
4
votes
3answers
596 views

Why does an algorithm need a keyspace?

Why does an algorithm need a keyspace? I thought the person encrypting would define his/her own key.
4
votes
3answers
222 views

Algorithm for computing square roots in $GF(2^n)$

Short question: is there an algorithm for efficiently computing square roots in $\mathbb{F}_{2^n}$?
4
votes
2answers
335 views

Can we say that if $P=NP$ there is no CPA secure public key encryption?

I've learned that public key encryption is based on the problem of Discrete Log (as regard to group theory) which believed to be hard. But, can we say that it doesn't matter on which problem our ...
4
votes
3answers
6k views

Which one of the Block Cipher modes is the best?

I have two questions regarding the Block Cipher Modes: Which one of the modes is considered the best? I know CBC has a problem of IV since the next block of the plain text is XORed with the result ...
4
votes
2answers
656 views

A patched SHA1 attempt for password verification

This is a classical scenario: For our web based authentication platform we have a username and a password field. User enters these values and presses Log In. The browser gathers the user data, ...
4
votes
2answers
2k views

Can a salt for a password hash be public?

For my understanding salts in password hashes are used to prevent the precomputation of $plaintext \to hashvalues$ (rainbow tables). I know from different threads, it is not necessary to keep the ...
4
votes
3answers
1k views

NIST temporarily closed — will that have a negative impact on the future of cryptography?

For those who didn't notice yet, in the USA, the National Institute of Standards and Technology(NIST) has been shut down temporarily because of the poor fiscal situation of the USA. The text at their ...
4
votes
2answers
507 views

Is this a structural weakness of Feistel networks?

I'm doing a lot of reading about Feistel networks. Something occurred to me a bit ago that I hadn't realized previously, namely that in any Feistel construction there are bits of the plaintext that ...
4
votes
3answers
634 views

P = NP and current cryptographic systems

I've recently heard some people claiming that if the fact that P = NP is proven, most (all?) the current cryptographic algorithm considered secure like RSA will be unusable in secure systems. My ...
4
votes
3answers
4k views

Export from US of crypto software with key-size > 56 bits still needs permission?

Elsewhere someone stated that he couldn't publish his crypto software on the Internet, because US Export Regulations require approval, if the key size is greater than 56 bits. I know that several ...
4
votes
2answers
354 views

Why do we need Hash by key?

(i'm just trying to find what am I missing...) Assuming John have a clear text message , he can create a regular hash ( like md5 , or sha256) and then encrypt the ...
4
votes
2answers
3k 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 = ...
4
votes
2answers
625 views

Is this simple PRNG secure?

$G$ is a PRNG used in a stream cipher and defined in the following way: G receives $s_0$ as an input, which is a random string drawn from a uniform distribution. The output of step $i$ is $s_i = ...
4
votes
3answers
617 views

Combining several symmetric ciphers using XOR

I have seen a talk by Rüdiger Weis, where he says that you can combine two symmetric ciphers using XOR. According to him, that has the effect that its sufficient if only one of the ciphers is secure. ...
4
votes
2answers
306 views

Should I bother implementing DH + AES, or leave it to a library like Crypto++

I'm making a C++ back end for an application that'll heavily rely on AES-256 and DH. Should I trust third party libraries, or spend (lots of) time to learn about cryptographic implementation and write ...
4
votes
2answers
263 views

Can anyone give an example where (asymmetric) crypto can go wrong due to selection of wrong groups?

Basically the title says it all. It would be great if someone could tell give an example using provable security. More information about groups can be found at: ...
4
votes
4answers
377 views

Can cryptography be used to hide routing information from the router?

If Alice wants to talk to Bob and she has to involve a third party system run by Carol to establish, and possibly maintain, communications, then Carol knows that Alice and Bob communicated with each ...
4
votes
4answers
435 views

Knowing a valid salted hash for an unknown secret, is it possible to compute another valid hash?

$H(s,r)=d$ is a function that hashes the secret string $s$ with a salt $r$, and returns a digest $d$. $r$ may be arbitrarily chosen and each $r$ returns a different $d$. For any $d$, $r$ is known from ...
4
votes
1answer
1k views

Can SRP be used with Elliptic Curves?

I'm sure it can, because SRP (secure remote protocol) can be implemented everywhere where Diffie-Hellman works, but I need a proof to put this aspect into Wikipedia. Edit: ok, can it be at least ...
4
votes
1answer
904 views

What is a smart card?

In many cryptographic protocols, some information is transmitted within smart cards. So, what is a smart card? Is it a physical card? What are they used for in cryptographic protocols?
4
votes
2answers
3k views

Difference between symmetric and asymmetric hash function?

The Linux kernel supports symmetric and asymmetric hash functions. E.g. sha1, sha256, ... See tcrypt.c and search for test_hash_speed and ...
4
votes
3answers
4k views

Hill Cipher known plaintext attack

I know a plaintext - ciphertext couple of length 6 for a hill cipher where its key is a [3x3] matrix. Based on what I've read and learned, to attack and crack keys of [n x n], if we know a plaintext ...
4
votes
4answers
876 views

What is the actual difference between security through obscurity and true encryption?

In an abstract sense, aren't both the same? Don't their definitions boil down to the following? security through obscurity: trying to make sure some information cannot be obtained without knowing ...
4
votes
3answers
1k views

What algorithm would give the shortest ciphertext for very short plaintexts?

I have to encrypt some very short messages (approx. 5 characters) and I would like the ciphertext to be as short as possible. I am currently using AES but the initialization vector (IV) is making my ...
4
votes
1answer
6k views

How can I convert a DER ECDSA signature to ASN.1?

I having trouble verifying an ECDSA signature signed using client side javascript with Java/BouncyCastle. The javascript signing function source: ...
4
votes
3answers
439 views

Is this “layered” XOR cipher secure?

I am aware of the vulnerabilities of simple xor ciphers and recently I came across a block cipher that claims to solve those vulnerabilities. The cipher goes as follows with both the block and key ...
4
votes
4answers
863 views

Two different keys decrypting same content

is there some generally available algorithm which will encrypt a short string and generate two unique keys so that any of the two can be used to decrypt the message again? It doesn't has to be "super ...
4
votes
2answers
4k views

Why is HMAC-SHA1 still considered secure?

This Q & A http://security.stackexchange.com/questions/33123/hotp-with-as-hmac-hashing-algoritme-a-hash-from-the-sha-2-family says that the security of HMAC-SHA1 does not depend on resistance to ...
4
votes
4answers
688 views

Alternative to NSA encryption algorithm

I am looking for a strong alternative to elliptic curve cryptography. It should be something that could face quantum computing attacks, but nothing created by the NSA. I heard about isogeny key ...
4
votes
2answers
3k views

Why is a 2048-bit public RSA key represented by 540 hexadecimal characters in X.509 Certificates?

In the public certificate, an RSA public key specified as 2048 bits long is represented by 540 hexadecimal characters. Converted to base-2, this yields 2160 bits, 112 more than the stated 2048.

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