0
votes
0answers
28 views

Question about AES and Cryptsetup [migrated]

I've read that AES can work with three key sizes: 128 bits, 192 bits and 256 bits. I'm trying to set up a LUKS partition with CryptSetup, using “aes-xts-plain64” cipher. Why can I create keys of any ...
1
vote
1answer
131 views

A way around digital signatures?

Scenario: I have to protect the integrity of some files that will be exchanged between entities $A$, $B$, $C$. Entity $A$ creates the file (e.g. configuration) and sends it to $B$ and $C$. Entities ...
3
votes
3answers
193 views

How feasible is word-level frequency analysis over English (or any language)?

Say I have some black box which, given any English word, deterministically outputs a token for that word. Assume our black box is implemented using strong cryptography, i.e. the hardness of reversing ...
2
votes
1answer
93 views

Straightforward method for hampering frequency analysis on deterministic encryption

I'm brainstorming some different ways of making deterministic encryption more secure. I want to use deterministic encryption to preserve searchability over the keywords in a document set. However, I ...
9
votes
2answers
172 views

How exactly does key whitening manage to increase security?

Wikipedia states that key whitening increases security: In cryptography, key whitening is a technique intended to increase the security of an iterated block cipher. It consists of steps that ...
7
votes
1answer
166 views

How many degrees of freedom up my sleeve?

Now that we know how the MD2 S-box was constructed, I find myself wondering how good a nothing up my sleeve number it really is. It is derived from $\pi$, but not in a very obvious way, even in ...
4
votes
0answers
51 views

Homogenous and heterogeneous Unbalanced Feistel Networks

Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round). The advantage of heterogeneous UFNs ...
2
votes
1answer
95 views

How to only encrypt a subset of the plaintext

I was wondering if there is a smart way for a user to only encrypt a subset of a plaintext. I'll try to be more specific. Let's suppose the user U wants to use a special cipher such that given a ...
2
votes
2answers
77 views

ECDSA with SHA256 and sepc192r1 curve: Impossible, or how to calculate $e$?

I need to use ECDSA as the signing algorithm and SHA256 for hashing the message. I'm running into troubles verifying the signature calculated on two different platform (one is BouncyCastle, another ...
2
votes
1answer
314 views

Interleaving bytes to make an effectively larger block size

Will applying a 16 byte bit block cipher such as AES over a 256 byte block to in the following way result in a much stronger cipher:- Apply block cipher with first key digest to each 16 byte group. ...
5
votes
2answers
179 views

How does Truecrypt change password without the need for a complete re-encryption of volume

From what I understand: TrueCrypt takes the password as message Add salt calculates a digest use digest for encryption From what I understand. A good hash function has Second pre-image ...
2
votes
2answers
79 views

Skein or Keccak stream cipher construction

I am wondering if using Skein or the Keccak hash algorithm in this construction (as a stream cipher) is secure: $H$ = Keccak or Skein hash with a 256 bit output $K$ = The main 256 bit random key, ...
1
vote
1answer
47 views

Size of Fresh Ciphertext's Noise in FHE over the integers

I'm studying FHE over the Integer which is https://eprint.iacr.org/2009/616.pdf In the remark 3.4, it says that the fresh ciphertexts have noise at most $2^{\rho'+2}$. I don't know why that ...
2
votes
1answer
262 views

Revealing random bit permutation

I am new in cryptography. I want to determine the complexity of revealing a random bit permutation which is used as block cipher for plaintexts (bitstrings of length n). An adversary catches different ...
2
votes
1answer
55 views

Secure MultiParty Computation with secret inputs for secret outputs

I want to know if it’s possible to use a SMPC (Secure Multi-Party Computation) to have $N$ entities compute the outcome of a known mathematical operation with two or more secret inputs, where each ...
1
vote
1answer
54 views

where to keep the AES keystream?

I am trying to implement an AES encryption on my messages in my app and I want to have a different keystream for each "message group". Therefore, currently I am holding the keystreams in the database ...
0
votes
0answers
34 views

References and resources for learning to implement crypt. algorithms? [closed]

I wanted to learn about cryptography so they recommended me some of the books of Bruce Schneier. I'm now reading Cryptography Engineering and planning to follow with this one ...
2
votes
1answer
53 views

Constant data as input to hash

I want to use hash function on some data, and part of this data, might be constant for a certain period. The output of the hash function is used as authentication data (MAC). I want to know if there ...
0
votes
1answer
70 views

About S-box in AES

I am working on AES. Can we expand $s(a \oplus b)$ in terms of $s(a)$ and $s(b)$ where $a$ and $b$ are two eight bit inputs and $s(a)$ is the S-box value of $a$?
8
votes
4answers
266 views

Using hashes as passwords

I have thought of a system for generating passwords which works as follows: Take the following items: A password, such as williamwallace. A secret 1000 digit ...
3
votes
1answer
88 views

Public key in fully homomorphic encryption over the integers

I'm reading “Fully Homomorphic Encryption over the Integers” by van Dijk et al. I wonder why $x_0$, which is a component of the public key, should be an odd number?
4
votes
1answer
59 views

point addition equation in projective co ordinates

How can I get point addition equation for elliptic curves in projective co ordinate system ? Can I get it by changing $$ x = X/Z $$ and $$ y =Y/Z $$ in the equation for affine co ordinates' group law ...
2
votes
2answers
336 views

Cryptographically Secure Hash Algorithm with Very Specific Property

First of all, I apologize if this is a stupid question, but I don't have any background in cryptography. I'm looking for a secure hash algorithm $H$ with the property $H(K_1+n)\oplus ...
2
votes
1answer
41 views

run length testing [closed]

Looking for guidance/references with/about calculations: I am designing a widget that creates N-bit binary sequences. My customers target spec for the sequence's minimum entropy is X bits/bit. I plan ...
1
vote
1answer
72 views

Is SRP post-quantum secure?

Just a simple one: is SRP-6a post-quantum secure? If not, are there any post-quantum secure "SRP-6a-like" alternatives?
2
votes
1answer
114 views

Simple proof of work example?

Can anyone show me a simple proof of work algorithm that I can use to stop spammers? I've looked at hashcat, but i think there's a bit too much specialized hardware for bitcoin mining. That is, the ...
3
votes
1answer
777 views

Theoretical attack on RSA

The high security of RSA is granted, because it is very hard to factorize $$ N = p * q $$ Nevertheless, there is actually no need of factorizing $N$, in order to generate the $Private$ $Key$, but the ...
2
votes
1answer
66 views

Composing and Inverting Symmetric Encryption Keys

Using a symmetric encryption algorithm $E$ on a message $M$, users usually send $E(M)$ to the recipient and then the recipient will compute $E^{-1}(E(M))=M$ to retrieve the message. For what symmetric ...
4
votes
0answers
56 views

Given a 'good' basis for a lattice, how can we solve the CVP?

I'm doing a little bit of reading about lattices. I read that if we can find a 'short' basis for our given lattice, we can solve CVP and SVP very efficiently. However, the paper didn't describe an ...
5
votes
2answers
174 views

Is perfect-forward secrecy achieved with RSA?

I am new to cryptography and am going through the book Understanding Cryptography by Paar and Pelzl. From what I understand Symmetric key distribution systems like Kerberos do not provide PFS ...
9
votes
3answers
286 views

AES-GCM Disadvantage

What is the disadvantage of AES-GCM mode for authenticated encryption? Why does the CAESAR competition say that it’s one of the goals to find an AE scheme that offers an advantage over AES-GCM? What ...
0
votes
0answers
18 views

How do I extract the private key components $N$ and $D$ from a private RSA key? [migrated]

I have a private RSA key like – for example – this one: ...
-1
votes
1answer
83 views

Questions on FHE over the Integers - the question modified!

I modified my question since it is not as specific as I wanted. I'm studying FHE over the Integer which is https://eprint.iacr.org/2009/616.pdf I got questions about the proof of Lemma A.1. In page ...
2
votes
1answer
41 views

Symmetric-key login protocol

I'm trying to analyze a login protocol based on symmetric key cryptography. I'm just starting out, so this may very likely be a very bad idea, but nonetheless I'd like to hear your thoughts on it. ...
4
votes
1answer
116 views

Using Lattice-based cryptography for TLS\SSL

Given the general benefits of Lattice-based cryptography, such as: Post quantum Security Security from worst case scenario Efficiency What could the outlook of shifting from RSA \ ECC-based ...
2
votes
1answer
50 views

PGP String to Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
3
votes
1answer
107 views

Is this an acceptable All-or-Nothing Transform?

I was thinking about AONTs, and designed the one below, I call it CHANT for Chained-Hash All-or-Nothing Transform; it's my very first shot at something of the sort, and was hoping I could get your ...
2
votes
1answer
46 views

Encrypted files in an encrypted partition or folder

Recently I started wondering about multiple encryption and found pages upon pages of posts and debates about the security of cascades. Now, don’t worry – I'm not looking for someone to discuss a ...
2
votes
0answers
80 views

Challenge-response based on public-key decryption, why send public key

Quoting the handbook of applied cryptography, chapter 10.3.3 (i): Identification based on PK decryption and witness. Consider the following protocol: $A \leftarrow B: h(r), B, P_A(r,B)$ ...
2
votes
1answer
87 views

Test Vectors for ciphers

While implementing ciphers (/hash functions, ...), I often face this problem: Where to find test vectors for it; so that I can guarantee my program is correct. It is generally a tedious job to find ...
-2
votes
0answers
44 views

Would it be possible to crack the key used for params given DES [duplicate]

I am working on a product that will link back to another product. The problem is the GET params on the target product are encrypted using DES (I believe) so the params look like... ...
1
vote
2answers
119 views

Public key Issue - same key pair as existing one? [duplicate]

My question is a bit naive, but what if someone generates the same RSA key pair as someone else? This person would have the same private key and so would be able to decrypt messages not intended to ...
2
votes
2answers
86 views

ECDH anonymous key exchange to avoid PKI

I want to use TLS to encrypt the communication between peers in a P2P network. Each peer has a well known 256bit peer identifier (the public key of a 256bit elliptic curve keypair). Both peers need ...
1
vote
0answers
14 views

TLS WG Charter and Security Goals [migrated]

I was looking at the TLS Working Group Charter. I noticed that confidentiality and integrity of messages for those who desire it are not goals for the group. Naively, I believe confidentiality and ...
4
votes
1answer
77 views

OTT service using FPE

Would it be possible to create an Over-The-Top communication utility that will encrypt voice using format preserving encryption (voice clear-text to audio encrypted stream) and send that over an ...
4
votes
1answer
117 views

Implementing CD serial key system

I am trying to create a system where to unlock the application one needs to enter a serial code. I have read many articles on the theme but there are two problems bugging me. One is, If I have a ...
6
votes
1answer
69 views

The REACT transform and Replayable CCA

Before stating my questions, let us recall the REACT transform [OP01], which enables to construct a CCA-secure hybrid PKE scheme, $\varepsilon'_{pk}$, from an OW-CPA PKE scheme ...
4
votes
3answers
122 views

Is it secure to use Diffie-Hellman key agreement to generate a nonce?

I have a system, using AES, in one of the modes that uses a nonce and authentication. We have a pre-shared key, and to agree about initial nonce we could use Diffie-Hellman, using the resulting ...
2
votes
1answer
201 views

Adding points on Elliptic Curves

How do we add the integer points $P=(-1, 4)$ and $Q=(2, 5)$ on the elliptic curve of the form $y^2=x^3+17$ ?
0
votes
1answer
121 views

Known plaintext attack on ElGamal encryption

Assume that Alice uses Bob’s ElGamal public key ( = 2, Yb = 8) to send two messages $M = 17$ and $M' = 37$ using the same random integer $k = 9$. Eve intercepts the ciphertext and somehow she finds ...

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