1
vote
1answer
40 views

tweakable block cipher and ideal block cipher

Can the set of block ciphers obtained from a tweakable block cipher (using distinct tweaks) be considered as the set of ideal block ciphers ?
1
vote
1answer
45 views

How secure is MD5 for one way authentication?

I have a server S1 with an Private String (PS) as an identifier shared with a server S2. Every 10 min S1 publish the hash value of PS+the current time which is used as public identifier (PI). Every ...
1
vote
0answers
26 views

How to approach to solve cipher text with fixed length key (which is repeating)?

I took a project to solve for lecture. In my project for a given cipher text(length 2031), I have a key (Picture of example is given.) which I do not know the length of it. So I started to try to find ...
4
votes
2answers
318 views

Security of the shared secret key for a smart meter (Linky)

Reading the specs of a new electricity smart meter (called Linky in France), I was surprised about the chosen encryption method (128 bits symmetric key AES), based on a single secret key (called CCC ...
4
votes
1answer
93 views

What is the major difference between FIPS 186-2 and FIPS 186-4?

Can anyone please tell me the major difference between FIPS 186-2 and FIPS 186-4? I know with FIPS 140-2 they want the DSS standard to be FIPS 186-4, but what difference does it make?
1
vote
1answer
22 views

How do two parties put together the AUTH data in the SKEME protocol?

SKEME is a Key Exchange protocol used in the Internet Key Exchange (IKE). It contains three phases: SHARE, EXCH, and ...
2
votes
1answer
119 views

Quantum vs. regular computing time to break ECC?

How long exactly would it take for a regular computer to crack an elliptic curve public/private key via bruteforce, vs. a quantum computer using Shor's algorithm with a couple thousand qubits? Can ...
5
votes
1answer
70 views

How many blocks can securely be encrypted with XTS

I could not find in the NIST recommendations on XTS how many blocks can securely be encrypted with XTS-AES. Through the recommendations, I've found: The length of the data unit for any instance ...
1
vote
1answer
25 views

Single-scalar multiplication with sign bit

I want to know if there's an "easy" timing-free way to compute the sign of $y$-coordinate of $r G$, for a secret scalar $r$ and $G$ the generator of an elliptic curve. We have several choices for ...
4
votes
1answer
47 views

Multiplying two additively shared values

Alice has $p_a,q_a$ and Bob has $p_b,q_b$, all elements of a ring $R$. They want to obtain shares of the value $pq$ where $p=p_a+p_b$, $q=q_a+q_b$. How do they do this ? Does revealing their shares of ...
1
vote
0answers
34 views

Possible enigma settings? [duplicate]

I'm writing an assignment about the Enigma machine, and i'm trying to calculate the amount of settings the enigma machine has. I have found several sites regarding this topic, but it seems like there ...
4
votes
1answer
136 views

differential cryptanalysis cipher for the final round

I have a problem to find the sub-key. The system is… For each round, we make the following stage: We add the round key $K_i$. Substitution : we have 8 blocks of 4 bits, and an S-box ...
-1
votes
1answer
34 views

Documents about ZUC

ZUC is a function that converts a string to another string. However, unlike a Hash function, ZUC converts a certain-length string to a any-length string. Can someone point me to its documentation or ...
3
votes
1answer
62 views

How can I convert a mathematical formula into a logical formula?

I'm using cryptominisat2.9.6 to solve equation set (including more than 160 equations). There are 160 variables in total, which are as follows: $x_0,x_1,x_2,...,x_{78},x_{79},y_0,y_1,y_2,..,y_{78},y_{...
0
votes
1answer
50 views

What is proper size of window Using RSA Window method?

I want to Use Window method for RSA modular Exponentiation. because of SCA. But I don`t know what is proper window size.
0
votes
0answers
26 views

Garbled table for 3 inputs

I have a truth table of a full adder with 3 inputs (A,B,Cin) and 2 outputs (S, Cout). How can I create a garbled truth table? I mean, in the general form it is ...
3
votes
2answers
76 views

Does a key need to be signed if it is being used to decrypt a message that is already signed?

I am trying to better understand authentication. Lets say I have posted my 128-bit AES symmetric key on some forum, encrypted asymmetrically to my friend using 256-bit ECC (25519). The forum isn't ...
3
votes
2answers
145 views

Should I add randomness at the end before AES?

Seen AES, changing a character drastically affects the encrypted text. I want to make it harder to decrypt AES I send. So, it seems this can be done by adding some special code and some random bytes <...
4
votes
2answers
62 views

Need for 3 rounds in Luby Rackoff theorem

I get that using Feistel network we can create a secure PRP from a secure PRF (in 3 rounds according to theorem). My question is why not just 2 rounds of Feistel network is sufficient. Is it that ...
9
votes
1answer
752 views

Does a big salt have the same memory effects as Bcrypt?

Citing Thomas Pornin on the question Why can't one implement bcrypt in Cuda?: bcrypt is a variant of the Blowfish key scheduling, which is defined over a table (a few kilobytes) which is ...
0
votes
1answer
61 views

AES GCM encryption, authentication and PBKDF2

I'm developing a kind of secret vault server application. The basic principle is similar to DPAPI where each secret will have its own unique random KEY/IV pair and and that KEY/IV pair will be ...
3
votes
1answer
267 views

AES 128 bits with 12 bytes IV vector composed of a 4 bytes counter : safe?

I have a 128 bits AES cypher (GCM, Galois/Counter Mode) using a 12-byte initialization vector (IV) composed of: 8 constant bytes: 6 bytes (device ID) 2 bytes (zero) 4 bytes (incrementing frame ...
1
vote
1answer
436 views

What is the random tape?

I am reading the paper "Toward plaintext-aware public-key encryption without random oracles" by Bellare and Palacio. So I can't understand what is the tape and random tape?
0
votes
0answers
59 views

How to calculate the exponent in modular exponentiation?

I have a problem when calculating power in modular, $a^b \bmod c = d$. where we can know values of $a$, $c$ and d, but we don't know values of $b$. example : $29^b \bmod 1024 = 365$. So, how can I ...
4
votes
1answer
71 views

How do I validate the AES cipher?

I have used AES CTR mode of operation. Each time a file is uploaded an encrypted file is obtained and the corresponding cipher is got – this is a mini project I have done. I wanted to know so as to ...
0
votes
1answer
43 views

FHE Block ciphers' usage

There are currently FHE implementation for AES Simon Speck, and may be more. Except for speed testing, amortized or not, one meaningful usage is mitigating form side channel analysis. Intel, AMD, ...
4
votes
2answers
111 views

RSA 3072 is 65,536 more difficult to factor than 2048?

If RSA 3072 is equal to 128 bit symmetric and 2048 is equal to 112 bit symmetric then 128-112= 16 and 2^16= 65,536. In that case wouldn't this make 3072 more future proof against quantum computers or ...
6
votes
1answer
204 views

How to assess the strength of the avalanche effect for AES?

Within the scope of a study project I'm looking for an approach to assess the quality of AES encryption in practice. To do so, I modified the OpenSSL source code to be able to log metrics while ...
1
vote
1answer
30 views

How to add passphrase to an RSA key?

If I want to protect a private RSA key, do I just XOR the password into the key, or do I do something else? Is it secure? Edit: I got a good answer from a comment - Hash the password/passphrase with ...
1
vote
1answer
36 views

Cracking vigenere of non-text cleartext

I've begun a course in crypto on coursera and the first homework was writing a vigenere(xor) cracker. It works, which was a rush :) but it makes one core assumption, one has encrypted a natural ...
5
votes
1answer
94 views

Generating an IV for AES-CBC

I am faced with the task of generating a secure 256-bit IV for AES-CBC. I possess the following resources: A 32-bit microprocessor A 32-bit PRNG (can read/reseed) A 64-bit clock counter (can read) ...
2
votes
0answers
201 views

The knife paradox?

In one of the hot forums of today on how to convince friends cryptography is good one of the arguments stated is the knife paradox, I was unable to find the answer on Google and my question is what is ...
2
votes
1answer
67 views

Cryptanalysis of XOR cipher with repeated key phrase

My assignment is to cryptanalyze cipher text that we know was encrypted with a stream cipher (bitwise XOR of plain text and key stream), and decrypt to plain text. We know the key stream is a repeated ...
5
votes
1answer
41 views

Can one make a secure AEAD from any secure cipher and any secure MAC?

Can one make a secure AEAD from any secure cipher and any secure MAC using encrypt-then-MAC: with independent keys and IVs (any cipher and MAC) if the cipher is a stream cipher (including a block ...
0
votes
0answers
20 views

Is there a reduction of security if I XOR Pkcs5S2 and SecureRandom?

I'm using this codereview sample to encrypt data. I would like to provide hardware protected encryption and a user password as the key. Is it acceptable to XOR the KDF Pkcs5S2 in Bouncy Castle with a ...
-3
votes
2answers
55 views

Is the one-time pad secure?

I have read about one-time pads (OTP) on Wikipedia. Is this secure? Can I actually use modular addition as ecryption like it said in Wikipedia? And the plaintext is as long as the OTP, so when I send ...
0
votes
1answer
22 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
68 views

Key exchange problem

I've found the following problem in one of my courses. Any tips on how to solve this would be appreciated! Alice has the key pair $(pka,ska)$. Bob has the pair keys $(pkb,skb)$. They want to ...
1
vote
0answers
24 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
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?
-2
votes
1answer
54 views

Randomness of a Key in a One Time Pad

The keys used in an One Time Pad are required to be randomly generated from a keyspace $\mathcal{K}$, we require 256 bit random keys, i.e. $\mathcal{K}=\{0,1\}^{256}.$ Suppose we randomly select an ...
1
vote
1answer
31 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) ...
2
votes
1answer
51 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 ...
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 ...
-1
votes
1answer
29 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 ...
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?
0
votes
1answer
29 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
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
1answer
89 views

New Improved Probabilistic version of RSA

On the 2nd page of "New probabilistic public-key encryption based on the RSA cryptosystem" by Roman'kov (PDF), at last it says Alice can find "f" of order "l" with least probability of (1-1/l). I ...
1
vote
0answers
61 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 ...

15 30 50 per page