0
votes
1answer
21 views

private-key can't be traced (GPG)?

I am very new to cryptography. I was reading about GPG/PGP Basics, and I have a doubt: As per my understanding, Everyone knows the algorithm (GPG) with which I generated my key pair. And If I give my ...
0
votes
1answer
1k views

How to calculate cycles per byte [duplicate]

Sometimes, websites and scientific papers that introduce and/or handle cryptographic algorithms also provide speed-analysis and tables comparing the individual performance of cryptographic ...
3
votes
2answers
729 views

Calculating cycles per byte

Cycles per byte seems to be a critical concern in designing and choosing stream ciphers. For example, from Wikipedia, RC4 has 7 cycles/byte on original Pentium chips. How is this calculated? Do they ...
1
vote
1answer
37 views

Application level encryption and key renewal

I had posted this question on stackoverflow and been asked to move it to crypto. What is your view on this? What is the doability? I have a question related to encrypting data in the database, at the ...
1
vote
0answers
21 views

MAC-then-encrypt: Using one-time-MAC with randomized CTR

The Coursera cryptography 1 course says: If you want to use MAC-then-encrypt mode then you should either use randomized-CTR or randomized-CBC. And if you use randomized-CTR then one-time-MAC ...
0
votes
0answers
33 views

Why there is time period of key pairs in public key cryptography? [migrated]

In Public Key Infrastructure, every key pair is associated with its life time. I don't understand why we have a life time when we have functionality such as certificate revocation list(crl) which ...
0
votes
0answers
12 views

Fixed initialization vector in aes cbc [duplicate]

What are the pros and cons of using fixed iv in aes-cbc encryption? I've read somewhere that it said using fixed iv doesn't really matter?
1
vote
1answer
186 views

Choosing primes in the Paillier cryptosystem

In the first step of key generation phase in Paillier cryptosystem given here. It's given that $$\operatorname{length}(p) = \operatorname{length}(q) ) \implies ...
1
vote
1answer
28 views

Is $E′(k,m)=E(0^n,m)$ semantically secure?

$(E,D)$ is a (one-time) semantically secure cipher where the message and ciphertext space is $\{0,1\}^n$. $E'(k,m)$ is defined as $E′(k,m)=E(0^n,m)$ The question is whether $E'(k,m)$ is (one-time) ...
0
votes
1answer
23 views

Is a KDF needed when using X25519 for ECDH and XChaCha20-Poly1305 for AEAD?

Is a KDF needed when using X25519 for ECDH and XChaCha20-Poly1305 or XSalsa20-Poly1305 for authenticated encryption? My hypothesis is "no" because the key from X25519 is less than 256 bits long; ...
0
votes
0answers
30 views

Is a good idea to generate a public key from a secret key using a functional encryption scheme?

FE - functional encryption PK - public key I want to design a PK cryptosystem that has a unique PK for each encryptor. Namely, the encryptor submits a unique value (or an attribute) to the private ...
0
votes
1answer
33 views

Get secret_value from multiple hashes md5(known_value_n + secret_value) [duplicate]

The attacker knows multiple hashes like md5(known_value_n + secret_value), for multiple known values. Does it help him to discover secret_value better then just single md5(known_value + secret_value)? ...
0
votes
0answers
21 views

Is ISAAC vulnerable to a cache timing attack?

Is the ISAAC stream cipher vulnerable to a cache timing attack in efficient implementations? It seems like it would (secret-dependent array lookups) but is it exploitable in the context of ISAAC?
-1
votes
0answers
15 views

Can the weak states in ISAAC be used for an attack?

Can these weak states in ISAAC be used for an attack? They have some of the 256 words equal to each other. There are a lot of them, but the weakest are rare and most of the biases (all of them for ...
-1
votes
1answer
28 views

Why would a 3DES key decrypt one block, but not the next?

I'm trying to crack an encrypted data stream. It appears to be using a 64-bit 3DES key (as written in the application logs), and in fact using that key does correctly decrypt the first 64-bit packet ...
1
vote
1answer
86 views

Encrypting and Authenticating The Simplex Communication Between Embedded Devices

I am planning to build temperature sensor nodes for my home heater control. Central device will control the heater using temperature data read by nodes. These nodes will send temperature data to ...
0
votes
1answer
19 views

Deriving Minimum Description Length of Substitution Key

Given a plaintext: Now is the time for all good men to come to the aid of their country because the quick brown fox jumped over the lazy dog. and a substitution ciphertext: Mpe od yjr yo,r ...
2
votes
2answers
73 views

comparison of security for identity based signature and Hashing (SHA-1) the identities

I would like to know which method can provide better security: using identity based signature or hashing the identities and message (using SHA-1) for authentication?
2
votes
3answers
129 views

How do I create a secure encryption scheme using addition?

You have a 4 number long PIN code with each number ranging from 0 to 9 which you wish to encrypt. You are then given a random 4 digit number ranging from 0 to 9999, which when added to the original ...
7
votes
2answers
121 views

Instantiating a random oracle

I am studying about RO model and just got this question that what are the factors that make it not possible to instantiate a RO with a Hash function. To give a reference on how far I know about them ...
2
votes
1answer
56 views

Multiplying integers modulo $2^{255}-19$ using the Curve25519 polynomial reduction algorithm

I'm reading the Curve25519 paper and I see that in page 11, under the title "Multiplying integers modulo $2^{255}-19$", it says: The coefficients of $x^{10}$; $x^{11}$; ...; $x^{18}$ in $uv$ are ...
3
votes
2answers
576 views

Creating serial key generator using ECDSA, how to get signature short enough?

I've written some questions in this stackoverflow and got great responses but now I'm trying to wrap it all together. I have for the last couple of weeks been building a serial key generator project ...
0
votes
1answer
439 views

Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack

While reading a literature on signature schemes, I came across the concept of Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack. Can anyone point me to the paper ...
2
votes
1answer
196 views

How is the AddRoundKey operation performed in AES-256?

Can anyone explain to me (or send a link to somewhere) how round keys are added in AES-256? I understand that the round keys is added to the state matrix for each round and how XOR works. But since ...
1
vote
0answers
57 views

How to normalize data of a generic HTTP request for the purpose of signing

I am working on PowerAuth 2.0, a solution for counter-based signing of HTTP requests (for the purpose of mobile banking). One of the tasks that I solved somehow but I am still not happy with the ...
9
votes
2answers
2k views

Why is the permutation in AES (and other ciphers) not random or key-dependent?

If the permutation in AES (or other ciphers) were randomly generated or dependent on the key, would it not be stronger against differential attacks? If this is so, then might we need fewer rounds for ...
3
votes
1answer
148 views

What is the probability of attacking SHA1 used in RSA signature with small exponent?

There is RSA signature check which has following properties: RSA modulus N which is 2048-bit RSA public exponent equal 41 (0x29) Genuine Signature uses EMSA-PKCS1-v1_5 padding of SHA1 hash, however ...
38
votes
7answers
35k views

Are there two known strings which have the same MD5 hash value?

Is there an example of two known strings which have the same MD5 hash value (representing a so-called "MD5 collision")?
0
votes
0answers
27 views

Probability of IV/key reuse

I generate randomly both an initialization vector (IV) and a symmetric key (key) to feed an authenticated encryption scheme. How much IV/key combinations can I generate until the same combination ...
2
votes
1answer
146 views

In HMQV, can one use multiple identities with one public key?

The HMQV protocol has 2 "identity" fields $\hat{A}, \hat{B}$ that are used in the dual signature - and it tries to guarantee that any properly-generated session key is only shared by a single $(A, B, ...
1
vote
1answer
65 views

What are coding schemes for timing channels

I know we can hide information in the inter-packet delays, e.g. we can generate a code-book that each code-word corresponds to a message and is generated by realization of a specific random process. ...
0
votes
0answers
31 views

Has anybody implemented BGN cryptosystem to multiply two plain texts?

I have tried to use this code as follows, http://stackoverflow.com/questions/33581962/bgn-implementation-in-java but the issue is, when it generate the pairing, the output is in GTfiniteelement (for ...
5
votes
1answer
98 views

Transforming SHA-512 into SHA-512/256?

Based on my skimming over FIPS 180-4 it looks like the only difference between SHA-512 and SHA-512/256 is the initial hash value and the fact that the final output is truncated to 256 bits. My ...
3
votes
1answer
55 views

Difference between FleXOR and Free-XOR

I would like to know the differences between FleXOR and Free-XOR. I searched in the web but I couldn’t understand the information I found. I understand that there are both cryptographic methods as ...
2
votes
1answer
36 views

What's the difference between PBKDF and SHA and why use them together?

I've been reading a little bit about hashing lately and according to AgileBits, they use "SHA512 within PBKDF2" in their new vault file. I've looked in Wikipedia for both names and I know PBKDF2 is a ...
3
votes
2answers
64 views

Is Schannel supposed to use SHA1 for (EC)DHE params?

I captured a TLS 1.2 handshake on my server (WIN2012.R2/IIS 8.5) and noticed that SHA1 is being used to hash ECDHE parameters despite both the server and client(s) supporting SHA2 signatures. ...
6
votes
2answers
64 views

How to test implementation of primality tests like Miller–Rabin?

The Miller-Rabin primality test is an algorithm for checking if number is a prime. What would be best way to test implementation of such algorithm (or any primality test in general)?
21
votes
2answers
2k views

Why is PuTTYgen-created RSA public exponent(e) not in {3,17,65537}?

As far as I know, RSA public exponent(e) should be one of {3,17,65537}. However, I found PuTTYgen-created RSA public exponent(e) is 0x25(37) by default,as follows, (PuTTYgen version: 0.66) I am ...
3
votes
2answers
121 views

What is a purpose of reducing lattice basis?

This may be too broad question but it is not. I have been studying lattices for few months now, more specifically I studied: lattice problems ($SVP$, $CVP$ and etc.) lattice cryptography in post ...
-2
votes
1answer
73 views

What is the security gain of applying Two S-boxes in Different Ways?

In a 128-bits Feistel Cipher: I need suggestions about two variations of the Round Function Variation-1 $64$ bit input is divided into $8$ bytes Byte $0,1,2,3$ are substituted with Sbox1 Byte ...
-1
votes
1answer
43 views

How do you work out the private key in a RSA cryptosystem knowing a certain public key?

The public key: n = 85 and e = 19 I know that n is the product of two prime numbers, now is it right of me to figure them out by process of elimination which I got p or q equals 17 and 5. Or is ...
0
votes
1answer
60 views

Zero Knowledge Proof extended Schnorr - average secrets

I am trying to compute and an overall average number of given secrets from inside the commitments. I have the following set-up: Three commitments; $C_{1}(id, num, r) = g_{1}^{id} g_{2}^{num} ...
1
vote
1answer
57 views

Are the following schemes based on a pseudo-random permutation secure?

I am currently working on the following task: Let F be a pseudorandom permutation. Consider the encryption scheme for the message space $\{0, 1\}^n$ defined as follows: $Gen(1^n)$ chooses ...
-1
votes
0answers
6 views

Effective ways to find partial sha1 collision [migrated]

I need to find 2 different string and compare their hash value. Both string must contain "abc". I looking for the first eight character that are the same and stop. I have been running for more than 24 ...
0
votes
1answer
47 views

How are security proofs done in ABE Schemes?

I have been studying several ABE schemes and I understand the security assumptions and the several types of security models used for the security game between the Challenger and the Adversary. What ...
1
vote
1answer
32 views

Why does Carter-Wegman MAC have 2n-bit output?

The Coursera course on Cryptography 1 has a section about Carter-Wegman MAC. Here is the image of slide: Now my question is both $F$ and $S$ output $n$-bit strings. We XOR two $n$-bit strings and we ...
1
vote
0answers
40 views

DTLS 1.2 Finished message

I am implementing DTLS 1.2 and using ECDHE_RSA_AES_128_GCM_SHA256 cipher suit. Below is my client finished message Can anyone explain this message? How many bytes for verify data? Is there ...
0
votes
1answer
44 views

CPA on theoretical OTP with CBC mode

Body of question Note: this is THEORETICAL exercise. I understand OTP and CBC does not get along. I have to find a CPA on CBC enc-mode using OTP as the encryption algorithm, s.t a new key is ...
2
votes
1answer
92 views

RSA Encryption problem for Discrete Math

I am doing practice problems for my upcoming final exam, and am having trouble with this RSA encryption problem. If any one could check to see if i did these correctly, it would be greatly ...
0
votes
1answer
58 views

How to decrypt an RSA ciphertext given an oracle providing the lower 8 bits of decryptions?

I have access to an oracle that can encrypt and partially decrypt a number with RSA-1024 algorithm. For encryption: \begin{equation} C = M^e\bmod n \end{equation} But for decryption, result will ...

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