2
votes
1answer
91 views

Encrypting decryption key

What's that property called when a scheme is secure even if you encrypt the decryption key? Some schemes have problems when your plaintext is the decryption key (or just the key if symmetric).
2
votes
1answer
164 views

Is AES-GCM length extension attack possible using authenticated decryption?

I am looking to encrypt a piece of data using AES-GCM with a full 16-byte GCM Tag and send it over the network using UDP. Is it safe to assume using the AEAD nature of AES-GCM that performing ...
2
votes
1answer
188 views

How to implement homomorphic multiplication for Elgamal?

I want to add the homomorphic property to Elgamal in libgcrypt. This is the core code I added to the library. ...
2
votes
1answer
112 views

Reduced message expansion in NTRU

In the original NTRU proposal from 1998, it says on page 16: It may be worth mentioning, though, that there is a simple. masking technique that can be used to significantly reduce message ...
2
votes
2answers
120 views

Group description in pairing based cryptography

Suppose we have a public key encryption scheme, in which public parameter contains $(p, G, G_t, e, g)$, where $p$ is prime number, $G$ is a (cyclic) group of prime order, $e:G \times G \mapsto G_t$. ...
2
votes
1answer
275 views

2048-bit RSA Decryption

If a message is encoded with 2048 bit RSA. The ciphertext is $M^e mod N$. In some cases, the message is short, $ M \approx 10^{20} $. With a high probability, $M$ can be written as $M = ab$ with $a, b ...
2
votes
1answer
88 views

How exactly is the output of the XOR step in PBKDF2 used?

I'm attempting to diagram PBKDF2 for a school project and I'm not 100% sure how to represent the XOR step. Specifically, I'm confused as to whether the output of the XOR step is used in subsequent ...
2
votes
1answer
167 views

Gap problem for Learning With Errors

Informally, a "Gap problem" arises when solving the computational (or search) version using an oracle for the decisional version. This definition of Gap Problem was introduced by Okamoto and ...
2
votes
1answer
114 views

Random Permutation polynomial

I need to know, please: (1) Is there anyway to pick uniformly at random permutation polynomial in a field of prime order? (2) Are there many permutation polynomials in a field? (3) In a finite ...
2
votes
1answer
333 views

Square roots, prime factorization

I´m stuck in my homework and since its homework, I would rather get some hints than full solution. The problem goes: factorize n = 88416763 in case that you know that the square roots of 51733469 ...
2
votes
1answer
419 views

Can public key be recovered from ciphertext & encrypted private key?

I'd like to implement something like a write-once public/private encrypted shared secret (no better quick description for the lack of terminology knowledge). I guess, I'm trying to implement HSM. The ...
2
votes
2answers
225 views

Encrypting twice with same key gives back plain text

I read in the answer here that when encrypting twice the plain text with same key could result in plain text as shown below $encrypt_{key}((encrypt_{key}(plain)) = plain $ Which block-cipher ...
2
votes
1answer
404 views

What are these twist attacks with cost $2^{58.4}$ on NIST P-224 curve, and when do they apply?

This page on Twist security mentions a combined attack and a twist rho attack, applicable in particular to NIST P-224 curve with cost $2^{58.4}$ something, with no mention precise definition of ...
2
votes
1answer
439 views

Frequency analysis of Vigenere Cipher

For Vigenere cipher, I understand Find period first (say we have p = 6) Find highest frequency of letter in each group (from 1 to 6) and assume it is "e" in plaintext What if we have more than ...
2
votes
1answer
177 views

Recover plaintext in passive attack of RSA of coprime public key

I have a situation in RSA like this. Charles sends same message $m$ to Alice and Bob encrypted with $e_A$ and $e_B$ respectively. It happens that he they are under same modulus $n$ and $gcd(e_A, ...
2
votes
1answer
282 views

Small Encryption Exponent

I am trying to crack an unpadded RSA set up for a homework. I have public key (R,e) and encrypted message E. ...
2
votes
1answer
168 views

Calculate the security of a cascade cipher

I’m reading “The Security of Multiple Encryption in the Ideal Cipher Model” and I’m having a hard time understanding something. How do I calculate the bounds of cascade cipher from the following ...
2
votes
1answer
477 views

AES-128 with weak key

Doing malware research (simple crypto locker) I found out that it uses AES-128 with weak key - every one of the sixteen bytes is represented by (a-z,A-Z,0-9). Thus simple brute-force attack should ...
2
votes
1answer
185 views

Understanding Pseudo Random Generators

I've been taking a crypto course online. I have a good idea how PRG's and Stream Ciphers work, but I'd love to get some input to help visualize what is actually happening. I understand a seed is used, ...
2
votes
1answer
686 views

Strong key generation using PBKDF

I know that PBKDF2 is very useful for generating strong keys. I'm trying to know is there any additional contribution of the given password to produce even stronger keys. Which key is more secure: ...
2
votes
1answer
135 views

Trapdoors for lattices

I refer to an article https://eprint.iacr.org/2011/501. I focus on (a bit modified) Algorithm 1 which runs as follows (in my understanding): For given $n, m\in \mathbb N$, $q=2^k$ and a distribution ...
2
votes
1answer
745 views

Isn't a simple Vernam cipher as secure as known symmetric key algorithms?

I have just read little about the Vernam cipher and the problems of implementing it. But, in practice, would not the key, if generated by a commonly used programming language's ...
2
votes
1answer
333 views

Is this correct way to generate stream cipher using AES CTR mode?

We are implementing searchable encryption techniques proposed by Song et al in Java for a paper[1]. The schemes need a Stream Cipher for achieving search over encrypted data. The stream of random bits ...
2
votes
1answer
175 views

Hill Cipher question

Recently, I was given three ciphers to crack for my cryptography class. At this point, I have guessed that one of them is likely a Hill cipher (probably 3x3, as that is the most complex we have done ...
2
votes
1answer
194 views

One Way function and Merkle Damgård

Is it possible keep the "one wayness property" of certain one way function in Merkle-Damgård construction? I'm asking this question because according to Collision-Resistant hashing: Towards making ...
2
votes
1answer
95 views

Variants of AES? [closed]

Would variants of AES provide the same level of security as AES, say by just replacing the S-box with another one, MDS matrix of Mixcolumn, etc.?
2
votes
1answer
94 views

Parallel variant of Carter-Wegman MAC with incremental property

Is there any variant of the Carter-Wegman MAC algorithm that is fast, parallel and has the property of incremental crypto?
2
votes
1answer
83 views

Verification of signed message with encryption

I have a question about the message that is being encrypted and signed. Say, two users called Tom and Mary, both have a pair of private key and public key. Tom sends a message through a system that ...
2
votes
1answer
85 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
142 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 ...
2
votes
1answer
86 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
1answer
149 views

Secure way to store fixed size string of digits

I need to store a string of digits (0-9) of a fixed size in my database securely. I've already performed a rainbow table attack on a plain hash, and it broke it in a matter of seconds. One option I ...
2
votes
1answer
385 views

Use AES-256 Or AES-CTR-256 For One Block?

I am have one block of data to encrypt that is 32-bytes long. Is it better to use the AES-256 primitive for this single block (not a stream) or AES-256-CTR, and also would there be any cons or pros to ...
2
votes
1answer
254 views

AES-CTR-256 Sub Keys With Encrypted Sub Key Index

I was working with some encryption and I decided to put a spin. To preface this would be used to encrypt multiple files. You start with a key file generated from random data. For example you could ...
2
votes
2answers
677 views

How secure is using a pad (using xor) on a encrypted data, for the purpose of obfuscating/hiding the underlying encryption?

Edit: I know this isn't really a one time pad (as pointed out), though I don't really know what to call it aside from just a pad, I guess. I have been reading around (mostly various stackexchange ...
2
votes
1answer
210 views

Generalized Merkle Signatures, SHA-3 and Sakura

Sakura specifies a tree hash mode for e.g. Keccak (SHA-3). Are there any reasons to use the Sakura tree hash mode in a Generalized Merkle Signature Scheme? It seems to me Sakura primarily solves a ...
2
votes
1answer
292 views

How to find which padding method is used in Block cipher(AES) encyption?

I have a cipher text which is encrypted using AES128 Algorithm. I want to know the following things to decrypt the cipher. IV (Initialization Vector) Padding Method Encryption Key How do I find ...
2
votes
1answer
94 views

mixing two asymmetrical random number generator streams

Knuth describes in "the art of computer programming part 2" an algorithm called "M" for mixing two streams of random numbers. This can be used to mix random number streams giving the assurance that ...
2
votes
1answer
437 views

What is the motivation behind Key-policy Attribute-based Encryption?

What is Attribute Based Encryption? has a nice explanation what both forms (Ciphertext-policy Attribute-based Encryption and Key-policy Attribute-based Encryption) are. My question is: what is the ...
2
votes
1answer
72 views

Is jacobian to projective conversion unique?

I am doing a small project in ECC. I have used the following equation for converting Projective to Jacobian coordinates: $$D = AC\\ E = BC^{2}\\ F = C$$ and also the following equation to convert ...
2
votes
1answer
200 views

Calculating IHVs from known message and hash output

Here is a somewhat silly and atypical problem I am currently facing. Usually, when it comes to hashes, one is bothered with finding collisions and preimages. My problem is, I need to find the IHV used ...
2
votes
1answer
841 views

How can I calculate the Rijndael SBox?

I would like to implement the Rijndael subBytes() operation using calculation instead of tables, because I like to play with this on different wordsizes, as an ...
2
votes
1answer
138 views

Simplification of a pairing

The paper Expressive, Efficient, and Revocable Data Access Control for Multi-Authority Cloud Storage contains the following simplification: $$e(C_i,\text{GPK}_{uid})\cdot e(D_i, ...
2
votes
1answer
212 views

Is a keyed PRF a MAC?

I remember I read that a MAC can be considered as a PRF. Can a variable-length input keyed-PRF be considered as a MAC?
2
votes
1answer
388 views

LFSR Output Sampling for Berlekamp-Massey

Looking at the use of Linear Feedback Shift Registers in cryptographic algorithms, I have learned that the Berlekamp-Massey algorithm can be used to find the (shortest) LFSR that generates a given ...
2
votes
1answer
82 views

Is HMAC padding the same as bcrypt?

I have been watching Christof Paar on his YouTube lectures also I used bcrypt to store two passwords with salts and I find that I have a few questions. I am interested in what bcrypt does to the ...
2
votes
2answers
209 views

Comparing two values without revealing them

Suppose Alice wants to prove to Bob that t1 is less than t2. t1 and ...
2
votes
3answers
1k views

Encryption of log files

I'd like to encrypt the contents of a log file that my application writes. The log system has the following characteristics: The file format is binary. Log files are left open while the application ...
2
votes
1answer
381 views

Pailler and Gentry - homomorphic encryption

Paillier cryptosystem is a probabilistic asymmetric algorithm for public key cryptography. Doesn't homomorphic encryption schemes have regular effects on the plaintext, and does that mean Pailliers ...
2
votes
1answer
422 views

What's the advantage of using OFB/CFB/CTR modes over a stream cipher

As far as I understand: The primary disadvantage associated with stream ciphers is the need for a random and unique key for each run in order to protect against reused-key attacks. OFB/CFB/CTR block ...

15 30 50 per page