-2
votes
0answers
30 views

How do Galios fields work in AES? [duplicate]

I am trying to learn how AES functions but I keep hanging at the subject of Galios fields. I am reading a lot about them but I just can not find an understandable explaination in how they work. Could ...
4
votes
2answers
637 views

Calculate the RSA private exponent from the CRT parameters

I am trying to make the RSA structure of Openssl manually, knowing the public key ($n$, $e$) and the CRT parameters $p$, $q$, $d_P$, $d_Q$, and $u = q^{-1} \mod p$. That is, I want to get the $d$ ...
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
41 views

Insecurity of CBC-MAC

Can anyone explain why CBC-MAC is not secure for variable length message? I read many books, but there are still some confusion. Such as the highlighted parts in previous pictures ...
3
votes
1answer
39 views

Is a chosen ciphertext attack on PGP still possible?

In a paper from 2002 (pdf), Jallad et al describe a chosen ciphertext attack on PGP by taking advantage of the CFB mode that the block ciphers use under PGP. It's quite a devastating attack. Is this ...
19
votes
3answers
13k views

How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint?

If cryptanalysts today were to crack the original Enigma machine, “how fast” or “how easily” could they do it? What methods would they use? The original cracking was significantly helped by operator ...
3
votes
1answer
47 views

The role of the dealer in visual cryptography

In visual cryptography schemes (VCS), there is special person called dealer. The dealer sets up the system, and the only one who knows about secret image. After encryption, the dealer distributes the ...
0
votes
1answer
37 views

Appropriate scrypt parameters when generating an scrypt hash

What values for CPU, memory and parallel difficulty should be used when generating an scrypt hash? i.e. ...
-3
votes
0answers
31 views

how a MITM attack works against tripartite in DH? [on hold]

Must Oscar change only the Key $K_{abc}$ (Alice, Bob and Charlie) or does he have one key for everyone of them ?
3
votes
2answers
590 views

How does blocksize affect security?

I have recently read about how blockciphers and how stream ciphers work, and although I think I finally got everything right, I'm still wondering how increasing blocksize increases security.
40
votes
1answer
4k views

What is a “freestart collision”?

In their work on SHA-1 collisions (cf. the EUROCRYPT-2016 paper “Freestart collision on full SHA-1” by Stevens, Karpman, and Peyrin) Stevens et al show that they are able to generate "freestart ...
4
votes
2answers
95 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 ...
-2
votes
0answers
20 views

Having trouble with a double encoded keyword sypher [closed]

IIYFATKOHRFDQLRTUKFOLDTIQLTFAZLGZFUNCKYCEFUCUQUGCWWOGYSOCZTXGZPNHYPMPQDOLNONAZOEQLUSEYELNUDEPQDOKPTIPQTYCZUZQQORUFANHQRGHIUJUQOEQQUWKEURLYHCSLUCUUUFKLUNAYLRUFAZQZONKYIGBKYITDOEAWGDPIKOOTRCUJLIGZWNSZGC ...
-2
votes
1answer
50 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 ...
0
votes
1answer
52 views

Key Hierarchy and key Encryption

If i have two 56-bit DES keys, and I use these two key to encrypt a 256-bit AES key. Like this $K_{AT}$ encrypts $K_{BT}$ and $K_{BT}$ encrypts $K$ What is the effective security of key $K$? Is it ...
5
votes
2answers
199 views

Finding the subgroup in isogeny-based cryptography

Isogeny-based cryptography is one of the newest post-quantum cryptography. Hardness of this system is based on finding isogeny between two elliptic curves. Also this is theorem: Elliptic curves ...
1
vote
1answer
36 views

McEliece variants that support signatures

Besides the Niederreiter cryptosystem, are there any other variants that support digital signatures? Can any of them sign arbitrary signatures unlike the Niederreiter cryptosystem? What are the key ...
1
vote
1answer
46 views

Expire signature

I am looking for a way to have a 'did it expired' key. There's a similar question here, but I have to prevent reusing of the 'did it expired' signature . A possible solution would be a two one-way ...
-2
votes
0answers
39 views

Man in the middle attack including 3 parties [closed]

How could a man in the middle attack work with 3 different parties in Diffie Hellman?
1
vote
2answers
71 views

How to break a 32 bit block cipher without key?

From what I know Skip32 is the only 32 bit block cipher and I heard its not secure. What do I do or which tool do I use to break a 32-bit block cipher? I did search for this but all I find is attacks ...
8
votes
3answers
11k views

What makes RSA secure by using prime numbers?

I am just learning about the RSA algorithm. Looking at the first two steps: Choose two distinct prime numbers $p$ and $q$. Compute $n = pq$. I have some probably stupid questions: Why do $p$ ...
1
vote
2answers
54 views

What does $\langle A, B\rangle$ mean?

I'm reading about CL-PKC and in Al-Riyami's FullIndent, I find some notations I must be sure to understand, to well explain it ...
14
votes
2answers
230 views

Formal verification in cryptography

I have seen in some places that people use formal verification and/or computer-aided verification for cryptography (tools like ProVerif, CryptoVerif, etc.). How do these approaches work?
4
votes
2answers
46 views

Motivation for the definition of statistical distance

Statistical distance is a widely used measure in cryptography for comparing two distributions. One can define various other measures for capturing the differences between two distributions, but why do ...
2
votes
3answers
1k views

Comparing Files: Is it better to use multiple hash algorithms or just one?

I'm looking to compare (for byte-for-byte equality) two binary files. I already have the process down: Check for existence etc. Compare file lengths Use a hash or CRC of a sort (right now I use ...
2
votes
1answer
29 views

What is the diffrence between Feistel networks and SPN?

I recently read about the concept of Feistel Networks and Substitution Permutation Networks but what is exactly the difference between the two ?
3
votes
1answer
40 views

Order of multiple encryption algorithms

as you can see on image above, in VeraCrypt you can select either Serpent -> Twofish -> AES or ...
0
votes
0answers
38 views

Is this Commitment Scheme binding?

Commitment scheme is given as follows: Alice chooses a random r the same size as x and calculates $y = h(x||r)$ where $||$ represents concatenation. Open: Alice sends x to Bob, and Bob calculates $y ...
2
votes
1answer
903 views

Hash algorithm with the least chance for collision

Out of these algorithms… MD5 SHA1 SHA224 SHA256 SHA384 SHA512 … which has the least chance of collision, and which is the most secure at the time of writing this?
0
votes
0answers
9 views

Time complexity looking up in a rainbow table

It is mentioned in the famous paper Making a Faster Cryptanalytic Time-Memory Trade-Off by Philippe Oechslin that: The total number of calculations we have to make is thus $\frac{t(t−1)}{2}$. ...
-4
votes
0answers
33 views

You can probably do this in your sleep [closed]

I have been working on a geocaching puzzle for a long time I have solved all the ciphers except this: YLVEYF GIIKAH I have done what plain text attack I understand (mainly affine, one time and ...
4
votes
1answer
33 views

Which values to store in rainbow table generation?

According to the Wikipedia and Philippe Oechslin's Making a Faster Cryptanalytic Time-Memory Trade-Off (pdf), both starting points and endpoints are keys. Here is an example from Wikipedia: As you ...
5
votes
2answers
255 views

How many possible Enigma machine settings?

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 are two answers to my question. The first answer is ...
4
votes
1answer
66 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?
5
votes
1answer
62 views

Difference between hierarchical and multi level secret sharing

In this paper, the definitions are simply as follows. Multi-Level secret sharing: Higher level participants can help lower participants to get the secret. Compartmented secret sharing: Each level ...
3
votes
1answer
110 views

Why should $a,b < N$ for Montgomery Reduction?

In Montgomery reduction, when calculating $a \times b \mod N$, it is required that $a \lt N$ and $b \lt N$. I think $0 \le T \lt N \times R$ is enough for the Montgomery Reduction. Rationale: Let ...
2
votes
1answer
115 views

Using e-ID Number for Encryption and Digital Signing

I want to use e-ID number for performing Encryption/Decryption and Digital Signing - and in order to do so, I've opted a PGP-oriented approach which goes a bit like this. Generating PGP key-pair ...
-1
votes
0answers
33 views

A symmetric key construction not based on XOR [closed]

As far as I'm aware, one of the symmetric key constructions which is CPA-secure is $c = \langle r, m \oplus F_k(r) \rangle$. For designing a specific system I need a symmetric key construction which ...
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 ...
2
votes
1answer
52 views

Get $a$ such that quadratic residue has a solution (Rabin)

My task is to implement Rabin signature. I have trouble with choosing padding a such that $$x^2 \equiv a \pmod n$$ has a solution. In that context, $n=p\cdot q$ is composite, where $p$ and $q$ are ...
4
votes
2answers
296 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 ...
10
votes
1answer
425 views

Compact digital signature for noisy data

The question asks for a signature scheme, with a public verification procedure, that is tolerant to minor alterations of the signed data during its transmission [possibly in analog form over some ...
18
votes
3answers
39k views

Difference between stream cipher and block cipher

A typical stream cipher encrypts plaintext one byte at a time, although a stream cipher may be designed to operate on one bit at a time or on units larger than a byte at a time. A block cipher ...
0
votes
2answers
49 views

Need help choosing algorithm and topic [closed]

I am not pretty sure if this is the right place, but I have searched a lot and still cannot decide what to do. So here is why I am typing here - I am studying last year computer science and therefore ...
1
vote
1answer
71 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 ...
1
vote
1answer
41 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 ...
2
votes
1answer
233 views

How long does it take to decrypt an RSA/ECB encrypted message?

I am working on assignment where I have specific scenarios and I am little bit struggling with this one. Alice sends and email to Bob.For this e-mail, she uses the following method of encryption: ...
4
votes
1answer
111 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 ...
0
votes
0answers
22 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 ...
5
votes
1answer
67 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 ...

15 30 50 per page