2
votes
2answers
120 views

cipher text only attacks on deterministic homomorphic encryption schemes

If we consider a set of numbers say a set $s=\{a,b,c,d\}$ , where $a,b,c,d>1$ and the numbers $a, b, c, d$ do not share any relation between them , i.e. for any two numbers, $n_1,n_2\in s$ the ...
4
votes
1answer
96 views

Why is the re-encryption algorithm in Universal Re-encryption for Mixnets more complicated than apparently necessary?

This is the paper. On page 6, the paper describes a variant of El Gamal and a way of re-encrypting ciphertexts. I thought an easier way to do encryption is to output $(m(g^x)^y,g^y)$, and universal ...
0
votes
1answer
280 views

what are the most common stream ciphers algorithms? [closed]

say that we have an unknown stream cipher which output bytes and which have more than 10 years of existence. What can be the most probable algorithms if we consider the most 'populars' stream cipher ...
4
votes
1answer
72 views

On Proving That a Primitive Does Not Exist

In the paper of Hsiao and Reyzin, Section $1.4$: Note that to show that no general reduction from $P$ to $Q$ exists requires proving that $Q$ does not exist Since the statement is about trying ...
4
votes
1answer
168 views

Generating PGP key *without* random generator? (using fixed input only)

I understand why in general, a strong random generator or source of entropy is used when generating PGP keys. However, I have a use case where I want to generate PGP keys deterministically, i.e. ...
0
votes
0answers
87 views

What is the danger if a non-prime is chosen for RSA? [duplicate]

I was reading this question about generating primes for RSA keys. The answers point out that most implementations of of the algorithm use probabilistic prime-ness checking algorithms. The answer by @...
1
vote
1answer
126 views

How is wpa2 authentication structured

I would like to understand the cryptography behind Wpa2. As far as I know, there are 4 messages on the 4-way handshake and three of them are values concatenated with hashes. First, I am trying to ...
2
votes
1answer
341 views

Attack for RSA 1024 bit with Low Public Exponent

I am facing a challenge at university. Our teacher give us the challenge to try to break an RSA 1024 bit. We have public modulus N and public exponent e (0x03), we don't know the padding. We have a ...
4
votes
1answer
182 views

Implementing AES MixColumns with fewest XOR gates

I'm playing with Contiki (O.S. for constrained devices such as sensors and micro-controllers) and particularly with the AES encryption in software (the one available in Contiki source code). I'm ...
0
votes
0answers
96 views

Side channel attack on FPGA AES engine

I actually don't know if this is the right place where ask, but I try. The side channel attacks aren't a negligible problem. There are several ways to protect from these attacks its own IP inside the ...
5
votes
4answers
727 views

Which symmetric cipher is best for studying? [closed]

I would like to study a modern symmetric cipher (I have never studied a cipher before) and I was wondering which would be the best cipher for studying purposes of the following: AES (Rijndael), ...
1
vote
1answer
58 views

How to determine the exponent when using RSA

Can someone please explain to me how, when using RSA, to determine the exponent to be used in encryption and decryption? I have attempted a worked example on using RSA (shown below) but I can't ever ...
2
votes
3answers
66 views

Frequency tables for HTML page source

Are there online resources with an ASCII character frequency table for HTML? There's tons of them for english, but I can't seem to find one for page source. I know that this is something that's ...
0
votes
1answer
75 views

What is more efficient, pairing based cryptography or non pairing based cryptography? [closed]

As far as I know non pairing pairing based cryptography is less time consuming than pairing based because, pairing based uses complex operations. Are there any advantages of pairing based cryptography ...
1
vote
1answer
118 views

SSH rekey security implications

When an SSH session is rekeyed due to either the time limit or data limit for rekeying having passed, does the Diffie-Hellman exchange take place within the encrypted channel provided by the existing ...
2
votes
0answers
49 views

Determine safety of exercise hash functions [duplicate]

There have been several attacks against hash functions such as $h_{sha1}$ and $h_{md5}$. Professor A suggests a new function $h_{666}$ with an output length of 666 bits. Professor B suggests ...
1
vote
1answer
65 views

Determine if encryption is safe against CPA

The following encryption scheme encrypts each block of length $n$ of the plaintext separately: $c_i = k_1 \oplus F(k_2 \oplus p_i)$ Where $F$ is a strong pseudo-random permutation (i.e. it is easy ...
2
votes
1answer
181 views

How broken is a xor of two multiply with carry generators?

How broken is a xor of two LCGs? How Brittle Are LCG-Cracking Techniques? Based on the above two questions, I have simply one additional question: how broken is a XOR of two 64-bit multiply with ...
10
votes
3answers
319 views

Collision or second preimage for the ChaCha core?

Daniel J. Bernstein's ChaCha core is an evolution of the Salsa20 core. Both are functions over the set of 512-bit bitstrings, partitioned as sixteen 32-bit words. Can we exhibit collisions, or second-...
3
votes
1answer
307 views

Understanding Meet-in-the-Middle attack on block ciphers

I understand how to implement a Meet-in-the-Middle attack on 2DES/3DES, by computing for one half all possible keys and storing the outcome and then subsequently do the same for the other half but ...
3
votes
0answers
87 views

Worst case one way function

the worst-case one way function is defined as follows $$\forall A \exists x : pr(A(f(x))\in f^{-1}(f(x)))\neq 1$$ can you give any example of such function?
0
votes
1answer
650 views

What is Polymorphic encryption? [closed]

Well i have downloaded some cryptographic algorithm. Do there are those I didn't understand so this is my question: What is polymorphic RC4 or Polymorphic xor encryption? I heard this in malware ...
2
votes
1answer
125 views

Eavesdropping experiment with private key

I am extremely new to cryptography, still trying to learn basics. I got stuck in the following example of an eavesdropping experiment with a private key. $$\begin{array} {|r|r r r|r|} \hline C & &...
-1
votes
2answers
240 views

SQL-Like queries in CRYPTDB doesn't work [closed]

I have downloaded and built Cryptdb and it works well. Most of queries on encrypted database run without any issue but, the query with LIKE key word receives an ...
2
votes
1answer
347 views

How are subkeys, in Feistel block ciphers, derived for each round?

I'm bit confused about the subkeys that are used in Feistel ciphers. I know that all the subkeys ki are derived from the main key K, but how? Say I have a simplified Feistel block cipher of i rounds, ...
3
votes
1answer
135 views

Is secure communication without public-key crytography feasible?

We all know about public-key cryptosystems, and we know some of these are computationally secure (for the time being, of course). Are there any algorithms out there which allow safe communication ...
-1
votes
1answer
53 views

Cardinality of the key space $\{0,1\}^\ell$

Imagine we have a scheme whose key is chosen from the set $\{0,1\}^\ell$. My question is: What is the size of key space for this scheme?
3
votes
2answers
563 views

What's the GCM-SHA 256 of a TLS protocol?

If we read the Google line information about how the cypher the https communication, it reads: TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 I understand it's using ...
0
votes
1answer
149 views

2DES vs. two-key triple encryption, with no decryption step

So studying double encryption (double DES) and understanding why it is subject to a Meet-in-the-middle attack, I tried to see if the same attack could be applied to a triple encryption with only two ...
6
votes
1answer
256 views

What is “witness encryption”?

I recently skimmed over tho papers on time-lock encryption: “Time-release Protocol from Bitcoin and Witness Encryption for SAT” by Liu, Garcia, and Ryan “How to Build Time-Lock Encryption” by Jager ...
-1
votes
1answer
28 views

Relationship between an elements order and the DLP [closed]

How can I use these properties to attack the DHKE? I know that the order of $a$ is always $2$ for $a = P - 1$ in $Z_p$. The subgroups generated by a will be $\{1,a\}$.
4
votes
2answers
142 views

Turning a 64 bit block cipher into a 128 bit block cipher

There are quite a few block cipher modes of operation that require 128 bits. There are also modes of operation where a higher block size than 128, e.g. a block size of 256 bit would even be practical. ...
2
votes
2answers
124 views

3DES over Galois Counter Mode (GCM) for authenticated encryption

Is it possible to use DES or 3DES over Galois Counter Mode (GCM) to provide authenticated encryption? I haven't seen any implementation yet.
0
votes
1answer
66 views

Encrypt a file for multiple persons with different keys?

I thought a problem and want to ask if there's a more elegant solution. The scenario: A company with a fileserver, which hosts encrypted documents. The files need to be accessible by about a dozen ...
1
vote
1answer
150 views

Session key Exchange, some doubt

I have to find a solution to this problem: I have a network composed by 1 server and some client. The server has a couple of keys (public and private) and it shares a secret key with each client. My ...
1
vote
2answers
87 views

Concerns about use of MAC in my specification

Here is the pseudocode for a routine I am designing: ...
5
votes
1answer
2k views

What are the differences between collision attack and birthday attack?

From my understanding both types of attack, collision and birthday, are based on the principle of two randomly/pseudo-randomly chosen plaintext to hash to the same value. I don't want to launch any ...
5
votes
1answer
936 views

what are the advatanges and disavantages of the digital signature algorithms for JWT?

I am using a Java JWT library jose4j. There is a list of digital signatures algorithms which can be used. HMAC using SHA-2 RSASSA-PKCS1-V1_5 Digital Signatures with with SHA-2 Elliptic Curve Digital ...
0
votes
1answer
73 views

Encryption(AES) and verification per message

I want to send/receive messages with A (an peer) using TCP socket. I want to encrypt messages using AES CBC. Only I and A know a symmetric key K1 used in AES CBC, and K2 used in HMAC. The size of each ...
1
vote
0answers
28 views

Compromised Issuing CA [closed]

I'm configuring a PKI infrastructure with an offline root CA and several issuing CAs. Among other topics, I'm struggling to decide how the revokation of an Issuing CA certificate works. My Root CA ...
9
votes
2answers
138 views

Why develop Edward curve formulas that deviate from unification?

Edward curves were considered initially because they provide a unified formula for both doubling and addition, thus having inherent side-channel resistance. But a lot of work has been done recently ...
0
votes
1answer
65 views

is this possible to use asymmetric encryption schemes as order preserving encryption

Are we able to use order preserving encryption in asymmetric schemes, is this work efficiently. is this secure at any one of the situations
0
votes
3answers
113 views

How can complexity be increased or decreased in AES?

I have been studying data compression for a while. For educational purposes, after a lot of reading, I managed to create a software that performs encryption and authentication using AES256-GCM. ...
1
vote
0answers
31 views

Voting protocol - How many dishonest tallying centres can the protocol cope with?

We have the voting protocol that is described here. I am looking at the following exercise: Determine how many dishonest tallying centres the protocol can cope with before the following properties ...
2
votes
1answer
51 views

Establish Trust By Signing Random Seed

I'm trying to get my server to establish trust with a client. Neither is on the Internet, so there are no certificate authorities. The typical way to establish trust in my domain is for a client to "...
0
votes
1answer
83 views

What does the acronym “CRT” stand for in the PKCS #1 specification?

What does the acronym "CRT" stand for in the PKCS #1 specification? Does it stand for "Chinese Remainder Theorem"? Thanks, Pete
0
votes
1answer
798 views

What's the structure of server-key-exchange message during TLS handshake

Here is a relevant question: With OpenSSL and ECDHE, how to show the actual curve being used? Using ...
3
votes
1answer
126 views

Proof that two parties can communicate

Suppose we have three parties, Alice, Bob, and Carol. Alice can receive messages from Bob and Carol individually, but can only send messages to both simultaneously. Additionally, Alice cannot tell if ...
2
votes
1answer
133 views

Can I use an ECDH Shared Secret from the same Private / Public Key Pair?

I'd like to know if using the ECDH shared secret of a static EC Private Key with it's own corresponding static EC Public Key causes a problem / weakness. (edit) not asking if it's ok to re-use the ...
0
votes
1answer
273 views

How HMAC.Update function works?

I know how standard HMAC(key,msg) function works, and I want to write a Delphi port of HMAC class that implements Update function. The problem is that I don't understand how this Update function works ...

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