1
vote
1answer
49 views

Can I discard a specific X509 signature from file?

I'm writing a program to sign files using X.509 certificates and .NET framework classes. My users can sign the same file more than once without any problem (like a revision process). So, a file may ...
-1
votes
0answers
24 views

Meaning of Policy matches when signing SSL certificates

I was going over the process of doing a self-signed SSL certificate. The config file here is one of the inputs to this process (see: https://www.phildev.net/ssl/opensslconf.html) I have a question ...
1
vote
2answers
77 views

How to design a balanced LFSR with period 1023 and linear span 55?

I am trying various combination of LFSR's to try to design sequence of period 1023. The linear span should be 55 and the output 1023 bits has to be balanced. I have tried with five LFSR's with degree ...
0
votes
0answers
25 views

How does the openssl TLS implementation select the ciphersuite?

I would like to ask some help in pointing to me how the oopenssl TLS 1.2 server implementation selects the chosen ciphersuite? Does the server selects the first ciphersuite that is in the server's ...
1
vote
1answer
42 views

What is the logic behind Compress function in iterated hash function

I am working on cryptographic hash functions theorems. In the iterated hash functions part a specific word started appearing constantly: "Compress" for instance within the "compress function". I am ...
12
votes
4answers
4k views

Why is a known-plaintext attack considered a complete break?

I read somewhere that if a cipher has a known-plaintext attack, then it is considered completely broken. Say there is a cipher that someone uses where the algorithm is understood and a known-...
0
votes
0answers
20 views

Do I need output buffer to be multiple of AES block size for CTR mode? [migrated]

In my C code, I use OpenSSL's AES in CTR mode for encryption via EVP interface, that is I have something like this: ...
2
votes
1answer
65 views

SEAL Homomorphic multiplication

In SEAL homomorphic encryption library, there is an internal procedure to decompose a polynomial with large coefficients into a vector of polynomials with smaller coefficients. The procedure is ...
0
votes
1answer
134 views

What is Group in Diffie-Hellman?

I understand how Diffie-Hellman key-exchange works. Mainly, two parties agrees in a prime $p$ and a generator $g$. Then one party selects its private exponenet $x$, computes its public value $g^x \...
0
votes
0answers
30 views

CDH <=> and Square-DH. Square root problem

Here describes a way of proving CDH <=> and Square-DH. The thinkg I don't get - how to efficiently compute $CDH(U,V)$ from $CDH(U,V)^2$. Isn't Square root problem is hard in general? (In case of ...
2
votes
0answers
48 views

Avoiding doubled letters in encrypted text

I have an encrypted string based on an "alphabet" of 29 runes and access to successfully decrypted (runes->English) plaintext. Testing for a Vigenere cipher, I tried a Friedman attack (aka Kappa test, ...
0
votes
2answers
61 views

Is this RSA signing and verification process secure?

I need to verify that messages in a communications program are from valid senders. Below is a highlevel outline of how I think the process would work. The connections themselves are done over TLS. The ...
6
votes
1answer
129 views

Is solving $m^3 = k*n + c$ hard?

Given the equation $$m^3 = k\cdot n + c$$ I know $n$ and $c$, and I need to find $k$, so that $m$ is a natural number. $n$ and $c$ are large numbers, so i can't use bruteforce. How can you find a ...
5
votes
1answer
82 views

Strange notation using dollar sign

In the paper Multi-Signatures in the Plain Public-Key Model and a General Forking Lemma, the authors Bellare and Neven use notation which looks like left arrow with dollar sign above it. Authors ...
1
vote
1answer
19 views

Extra attributes in a certificate signing request

When creating a certificate signing request, there is a part where openssl says "Please enter the following extra attributes to be sent with your certificate request". One of these is a challenge ...
-1
votes
1answer
80 views

Can I calculate $d$ given only RSA’s $c$, $n$ and $e$?

The question “Calculating RSA private exponent when given public exponent and the modulus factors using extended euclid” assumes the factors are known. This got me wondering if it is possible to ...
1
vote
1answer
57 views

Is a stream cipher similar to One-Time Pad using hash secure?

I've read some Q&A about combining OTP with hash on this site, but I still wonder why some answers said that using hash for OTP key is not strong enough to resist brute force attack? Assuming ...
1
vote
0answers
85 views

proving indistinguishability of joint distribution using hybrid argument

Using Hybrid Argument, I want to prove following equivalence: $$\{X,Y,Z\}\equiv \{X',Y',Z'\}$$ by proving following equivalences: $\{X,Y,Z\}\equiv \{X,Y,Z'\}$(1) $\{X,Y,Z'\}\equiv \{X,Y',Z'\}$(2) $\...
6
votes
1answer
165 views

Least-weak way to authenticate using only AES ECB/CBC

I have an embedded application that needs to occasionally get secure updates from a server. The only crypto library I have available for the chip is an AES-256 cipher (ECB and CBC, encrypt/decrypt). ...
2
votes
1answer
45 views

Do reversible black box obfuscators exist?

We shall say that an obfuscator $\mathcal{O}$ is a reversible black box obfuscator if for each reversible program $P$ the obfuscated program $\mathcal{O}(P)$ is still reversible but does not reveal ...
-1
votes
1answer
75 views

Why does Paillier have poor performance?

Can anyone explain to me why Paillier crypto system does not provide good performance? I read here (pdf) that RSA and ElGamal provide better performance than Paillier algorithm.
2
votes
1answer
23 views

Can MGF1 within OAEP and PSS be replaced by a XOF?

Do we still need MGF1 as used in the PKCS#1 v2.x specifications for SHA-3 hash functions? MGF1 is currently used for OAEP and PSS as Mask Generation Function. Now that the SHA-3 specification contains ...
0
votes
0answers
23 views

Differential privacy with oblivious transfer

I have the following scenario: A has encrypted text, with max length $L$; B wants to know if the decrypted text, which contains one or more words from a closed group of $X$ words; A is not to be ...
6
votes
1answer
480 views

Difference between a circuit and a normal function

I've seen the word circuit used in many crypto contexts (for example, regarding FHE in this pdf). I've always thought of a circuit as another word for a program or function. But is there a difference -...
-1
votes
0answers
24 views

Assumption for security proof in the given scheme (identity based encryption)

In identity-based encryption schemes,mostly,assumption is used to prove the scheme. Using DBDH assumption,assume $T=aP,T1=bP$ and Given $[T,T1,rP,k]$ where $k \in e(T,T1)^{r}$ or not.Decide if $k=e(T,...
5
votes
1answer
107 views

Does adding more characters to the Enigma rotors improve crypto strength?

This seems like an obvious question but I haven't been able to find it, so here goes: Enigma is based on an alphabet of A-Z (26 characters); obviously this directly affects message content (e.g. ...
2
votes
1answer
56 views

Random oracles and independence

I'm reading an unpublished paper in which the author makes the following conclusions several times: Assumptions: finite probability space, $H$ is a random oracle, $X$ and $Y$ are two (not necessarily ...
0
votes
1answer
48 views

Given a sequence of integers, would applying AES encryption to the sequence produce a unique set of strings?

Let us say that we take a sequence of the integers from a to a+n-1: (a, a+1, a+2, a+n-1), ...
3
votes
1answer
389 views

When would I need DSA as opposed to RSA for digital signature?

The digital signature algorithm encrypts a hash using the senders private key and the receiver's public key. This multiple encryption is a pretty expensive process since public key encryption is so ...
3
votes
0answers
26 views

Is there a sufficiently memory-hard asymmetric encryption available? [closed]

The Password Hashing Competition offers several memory-hard hashing algorithms that are aware of time memory trade-off and essentially try to make it hard for ASICs and FPGAs to brute-force hashes. ...
3
votes
1answer
171 views

Can we develop a working asymmetric crypto message protocol without an asymmetric encryption algorithm?

Our crypto libraries have: DSA (4096, 512) DH (4096) AES (256) SHA (512) Let us say these are implemented directly in hardware so that trying to pull the pieces out is not possible, and the CPU ...
2
votes
1answer
62 views

One-wayness proof of Elgamal

Here in the proof of Elgemal one-wayness: Consider an adversary V that can invert random Elgamal encryptions with $ε$ probability. $V *$ : Adversary to compute the Diffie-Hellman function: ...
3
votes
1answer
72 views

Why is the simulation required in these identity-based encryption security proofs?

In identity-based encryption papers (i.e.this) it is very difficult for me to understand security proof. I don't know why they prove assumption (BDH, BDDH) for security of their scheme. Some uses ...
3
votes
1answer
46 views

Is using a rolling code as a constantly-changing shared secret effective for signing?

I am your average developer looking for some crypto-related guidance. I am trying to have assurance that a received message is from a particular sender, but have no need for the message content to be ...
5
votes
1answer
33 views

In PKCS#1 V2.2, should MGF be based on the same hash function that RSA-OAEP-ENCRYPT uses?

In Section 7.1.1 of PKCS#1 v2.2 there are two options for RSAES-OAEP-Encrypt given: Hash MGF Appendix B.2.1 of the same document states that MGF1 is based on a hash function. Is MGF1 based on the ...
8
votes
2answers
923 views

Why would Carter-Wegman-style message authentication not be broken by P = NP?

Researching about the implications of P = NP to cryptography I found someone say that the only cryptography left standing would be the one time pad and Carter-Wegman-Style message authentication. ...
4
votes
3answers
152 views

Are there encryption schemes with which it takes (significantly) longer to encrypt than to decrypt?

Are there encryption schemes with which it takes (significantly) longer to encrypt than to decrypt? I am thinking of a specific situation in which a server continuously receives encrypted messages ...
-1
votes
0answers
47 views

How do you do a linear feedback shift register?

I saw a video on YouTube by Daniel Rees. The video was about stream ciphers and showed how to do a linear feedback shift register. The example that was used to demonstrate how to do it is was like ...
1
vote
0answers
25 views

Some Question about Security Proof of authenticated identity-based encryption

In authenticated identity-based encryption by Benn Lynn, in proof of security, I have a little difficulties in understanding. In key extraction queries,if attacker request for guessed ID, then B fails....
7
votes
1answer
73 views

AES sbox security issue - power analysis attack?

I was wondering about whether the usage of a precomputed sbox (kind of a lookup table) could be a serious security issue when using AES. I am new to power analysis attacks, so it is hard to ...
0
votes
1answer
26 views

The Encode algorithm of Garbling scheme is probabilistic or deterministic?

In general the garbling scheme works as follows: Garb(1^\lambda, C): on input the security parameter \lambda in unary and the circuit C, it outputs a garbled circuit \widehat{C} and a garbling key ...
0
votes
1answer
40 views

Advantage of attacker in CPA secure IBE

In CPA secure IBE systems, the advantage of attacker (A) is defined as absolute value of $$Pr[b=b^{'}]-\frac{1}{2}$$ Can someone please explain this to me in a few words? Where exactly does that ...
5
votes
0answers
65 views

Distinguish two ciphers in Ring-LWE?

I am fairly new to this topic. so my question is: if I have $A=e_0a+e_1$ and $B=e_2a+e_3$ where $a$ is the agreed public parameter, $e_i \leftarrow \chi$ (drawn from the error distribution). if the ...
3
votes
1answer
35 views

What is many:1 and collision in MD5?

This is in reference to this answer on Stackoverflow. If you read the first paragraph of the answer, you'll find this line: It's always a many:1 mapping (meaning there will always be collisions) ...
1
vote
0answers
66 views

Why security proof uses random oracles in identity-based encryption?

In identity-based encryption, users decrypt the ciphertext by using private keys. Without private key, no one will be able to decrypt.In security proofs like here, random oracles are used with the ...
2
votes
2answers
59 views

In what sense addition modulo $n$ ($n>2$) isn't linear in the field $\mathbb{F}_2$?

I've been reading the Reason why “XOR” is a linear operation, but ordinary “addition” isn’t? question, in which one of the answers states that addition modulo $n$ ($n>2$) is linear in $\mathbb{Z}_n$...
1
vote
1answer
23 views

Encrypt a small amount of data with a password derived from PBKDF2

I have a small amount of data (about 128 bits) to secured with a strong password. I plan to run PBKDF2-SHA2-256 on the password and a 128 bit random salt to generate a 256 bit derived key. Then with ...
0
votes
0answers
24 views

Elgamal and Cramer-Shoup encryption: Given private key and ciphertext, can public key be determined?

I have a potential use case for Elgamal or Cramer-Shoup encryption which would effectively reverse the visibility of the public and private keys. The ciphertext and private key would be published and ...
3
votes
0answers
24 views

uf-cma and uf-cmva probabilistic MAC

Is there any simple probabilistic MAC $\Pi=(\operatorname{Gen},\operatorname{Tag},\operatorname{Vrfy})$ with UF-CMA security but without UF-CMVA security? How can an attacker efficiently use the $\...
6
votes
1answer
73 views

Definition of secure computation with more that two parties

In Definition of secure computation in m-party case with respect to semi-honest adversary (Definition 7.5.1 in Foundations of Cryptography: Volume 2, Basic Applications by Oded Goldriech) we say ...

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