0
votes
0answers
54 views

one complex password as a “seed” for localy generated per-service passwords

I've stumbled upon a project that suggests a way of having to remember one password, from which a “per-service password” could be generated by salting the service name using scrypt. What could be a ...
4
votes
2answers
704 views

ElGamal against chosen ciphertext attacks

In Hoffstein, Pipher, and Silverman's book An Introduction to Mathematical Cryptography, the authors make the following remark: An attack in which Eve has access to an oracle that decrypts ...
1
vote
1answer
97 views

Why we need ECDSA when we have ECDH?

ECDSA and ECDH give us the following methods: ...
0
votes
1answer
365 views

How to crack SHA256 only letters

I recently created a program that hashes a password using SHA256 and potentially using salt. How can I crack that if I know that the password only contains lowercase letters?
4
votes
2answers
211 views

Are all stream-ciphers IND-CPA?

A stream cipher usually generates a stream of pseudo-random bits which get XORed with the plaintext to form the ciphertext. The stream is generated using a given IV / nonce and a secret key. CTR-mode ...
1
vote
0answers
42 views

Clarify EC point addition and multiplication

Please clarify the below doubt regarding EC point addition and multiplication: $P$-Generator Point; $a$ and $b$ are integers; $X$ and $Y$ are EC points, defined as follows: $X = (a*P) + (b*P)$ $Y = ...
3
votes
1answer
81 views

Parameter choice Supersingular Isogeny DH

In “Towards quantum-resistant cryptosystems from supersingular elliptic curve isogenies” by DeFeo, Jao and Plut (PDF), the public parameters are defined as: Supersingular curve $E$, and bases $P, Q$ ...
1
vote
1answer
52 views

Degenerate discrete logarithm in binary field

Given a field $\mathbb{F}_{2^n}$, are there any choices of primitive element $g$ that make the discrete logarithm easier for that generator? That is, are there any degenerate cases? For example, if I ...
0
votes
1answer
17 views

PK systems using groups in practice

The four Public-key cryptosystems: RSA, ElGamel, DH, and Rabin (all with others) all require some group operations in an integer field or multiplication group of some residue classes. When it comes ...
1
vote
0answers
92 views

Where can I find names for cryptographic notation I don't recognize?

I'm new to this space and find myself stumbling over come cryptographic/mathematical notation. Search engines are not very helpful when copying and pasting Greek letters. Is there any reference that ...
1
vote
0answers
64 views

RSA algorithm assignment [duplicate]

Alice wants to share a symmetric key with Bob. She encrypts the small (64-bit) secret key $K$ with Bob’s public RSA key $(n,e)$ by padding it with zeroes to 2048 bits (the length of n) and computing $$...
1
vote
0answers
105 views

seemingly common error with OpenSSL and creating a PKS no certificate matches private key [closed]

I have a JKS store and export a signed cert (from the CSR generated in the store and signed) and the private key - I convert to PEM and attempt to generate a PKS from these two files. openssl.exe ...
2
votes
1answer
83 views

J-PAKE : About Schnorr NIZK proof for ephemeral private keys

Reading J-PAKE Authenticated Key Exchange Without PKI document : J-PAKE Round 1 : Alice sends out g^x1 and knowledge proof for x1, e.g : To prove the knowledge of the exponent for X = g^x1 ...
1
vote
0answers
78 views

AES-Paillier Homomorphic encryption [closed]

How can I implement following problem in java code for addition? (here I use Paillier homomrphic encryption): Input would be to generate a new AES key, encrypt the private data with that key, encrypt ...
9
votes
1answer
200 views

How many bits of entropy does an elliptic curve key of length n provide?

A FAQ for an open source project makes the claim: Indeed, an elliptic curve key of length n provides $n/2$ bits of security. I have two questions: What is the practical difference between "...
2
votes
1answer
241 views

How bad it is using the same IV twice with AES/GCM?

I understand that initialization vectors should not be used twice when using AES/GCM. I am using a counter as initialization vector. Every time I send out a new packet (I am developing an UDP based ...
3
votes
1answer
75 views

RSA: Range of public modulus

I know the public modulus is the product of two primes. For key with length L, the public modulus N should be such ...
5
votes
1answer
865 views

Ciphertext and tag size and IV transmission with AES in GCM mode

I am completely new to using AES in GCM mode of operation, and I have not a very large background in cryptography as well. I have been playing with OpenSSL trying to encrypt and decrypt some messages. ...
1
vote
1answer
110 views

Is one-time-pad still secure if the number of 1's in the key is revealed to the attacker?

For example, if $m = 10011$, $k = 11001$, $n=3$ (which is the number of 1's in k), $c = m \oplus k = 01010$. If $c$ and $n$ are revealed to the attacker, is this scheme still secure?
3
votes
1answer
239 views

Can there be a need for 1024-bit (symmetric) encryption?

I think we are all aware of the CAESAR-competition. Now the aim of this competition is to select a (portfolio of) winner(s) which provide authenticated encryption. I'll now assume that the results ...
3
votes
1answer
134 views

How does DPA work on AES?

I am really not much of a crypto guy so I don't really get how a differential power analysis on AES works. Can somebody explain it to me how it basically works?
2
votes
2answers
1k views

AES + CBC encryption for a stream of UDP packets

I am developing an application that is based on UDP, and I need to send a stream of packets. As you can imagine, packets can get lost or corrupted. I need to make sure that the content of those ...
8
votes
1answer
874 views

If RSA is only used to encrypt symmetric keys which are random, what's wrong with textbook RSA?

IND-CPA is used to protect against frequency analysis AFAICT. But if RSA is only used to encrypt symmetric keys (AFAICT) then what's wrong with using only textbook RSA because random keys are very ...
2
votes
1answer
91 views

Are all homomorphic encryption schemes not CCA secure? [duplicate]

Homomorphic encryption is hyped by computer sciences because it offers great potentials. For example you can perform cloud based calculation while nobody gets to know you data. I am wondering if ...
2
votes
0answers
26 views

Are there UFDs where the factorization problem is difficult but finding irreducibles is cheap?

Factorization of integers is hard, but finding irreducibles is expensive. Is there a ring where factorization is assumed hard but finding irreducibles is much cheaper than over $\Bbb Z$? It could ...
1
vote
1answer
73 views

About DH-EKE and ECDHE_PSK (PSK versus Pasword)

I am currently having a look at J-PAKE , so learning about Authenticated Key Exchange : Reading 2.2.2 E.K.E from this paper https://people.kth.se/~maguire/Erik_Ehrlund_Literature_Study_report_v1.2.pdf ...
4
votes
1answer
158 views

Quantum computing vs AES s-box equation

Do quantum computers have any affect on the ability to solve the non-linear AES s-box algebraic expression, or does solving it still fall under search algorithms (Grover's)? If quantum computer do ...
2
votes
1answer
67 views

Weakening of Pallier cryptosystem due to ciphertext equivalence and order in CryptDB

Pallier Cryptosystem is probabilistic in nature and IND-CPA secure. By design given two ciphertexts one cannot distinguish whether decrypting those two ciphertexts will result in same or different ...
1
vote
0answers
103 views

Is this a secure method of encrypting with authentication?

My goal is to allow two clients to send files securely over an untrusted network without the need for more than one block of information to be sent. Both clients have ECDSA keys of size 256 bits. I'd ...
4
votes
1answer
187 views

Parallelization of CFB mode encryption and decryption

While reading Evaluation of Some Blockcipher Modes of Operation by Rogaway (someone just linked it somewhere), I noticed two claims about CFB that I'm not sure I understand: Regarding whether CFB ...
2
votes
0answers
97 views

Does SHA-1 meet the strict avalanche criterion?

Does SHA-1 meet the strict avalanche criterion? I've been looking for a paper to cite on this, but haven't found one. It's something that seems to be easy to check (in "On the Design of S-Boxes", ...
3
votes
1answer
140 views

RSA with $\lambda(n)$ or $\varphi(n)$

The PKCS #1 v2.0 specifications suggest using $\lambda(n) = \mathrm{lcm}(p-1,q-1)$. What is the benefit of choosing $\lambda(n)$ over $\varphi(n) = (p-1)(q-1)$ in RSA key generation?
1
vote
1answer
153 views

Reversing Rotation + XOR

I have this cypher which is as follows : Take 2 numbers : A=1011 and B=1010 if the ith bit of A is 1 then shift B i times to the left. So in the end you will get ...
2
votes
1answer
99 views

Diffe-Helman Exchange result is always 1

I watched a video on Khan Academy explaining the Diffe-Hellman exchange. When I try to do an example problem, I get 1 all the time. Does the generator and prime modulus (or base on Wikipedia) have to ...
5
votes
1answer
211 views

Why have round constants in hashes?

This may seem like basic crypto knowledge, but why do hash functions like SHA-2 and Whirlpool have round constants that are absorbed into their respective states? I can understand that in a cipher ...
1
vote
1answer
134 views

What is the difference between a PRF and a PRF+?

What is the difference between a PRF and a PRF+? I am understanding them to mean the same thing, but I imagine that is because I don't understand their differences. The IKE RFC defines a PRF as: ...
-1
votes
1answer
44 views

different feistel words in key size

I have confusion on Feistel word in key size. Means, "what is the meaning of key size with different feistel word ?" What does m=2,3,4 represent? Where m represent different size of feistel word or ...
1
vote
1answer
149 views

SPI security of FE1 scheme

I have a question about security of FE1(Page 16-18) in paper "format preserving encryption". Can anyone explain me, why we are allowed to replace PRF with random function in security proof? And also, ...
5
votes
2answers
553 views

SHA-256 exhaustive search

How do I calculate the number of computations needed to break SHA256 in case we are using it for safely storing passwords (together with a salt)? Are there any formulas that can be employed? For ...
2
votes
1answer
54 views

Could a crypto system that uses non-FIPS crypto but then upgrades complete to FIPS be FIPS certified?

I know most people around here (including myself) are anti-FIPS, but I have a FIPS related question. Could a crypto system that is not FIPS, e.g. one based on primitives like Curve25519, achieve FIPS ...
1
vote
1answer
272 views

Calculating Multiplicative Inverse for Rijndael S-box using EEA

I am currently learning, and I'm stuck on something that I thought is very simple. On many academic sources they suggest using Extended Euclidean Algorithm to calculate the multiplicative inverse for ...
1
vote
2answers
121 views

How much pre-hashing a password increase security against brute force attack?

I am wondering how much hashing a password used as key for a symmetric key algorithm helps preventing brute force attack on crypted text. Let's assume I want to crypt text A using key B using AES-...
0
votes
1answer
117 views

Which is the most secure steganography technique? [closed]

Just like we have AES in crypotography, which is the most secure technique in Steganography? I am looking for a technique in which the standard image characteristic modifications it does go undetected(...
3
votes
1answer
86 views

Can I reduce the MAC size in TLS?

The MAC size is reduced to 80 bits in truncated_hmac extension , which says "forging of MAC values cannot be done off-line: in TLS, a single failed MAC guess will cause the immediate termination of ...
3
votes
1answer
52 views

Software interface for KDF and PBKDF?

I'm working on an implementation of Krawczyk and Eronen HKDF from RFC 5869. From Krawczyk's original paper, he identifies four inputs to a KDF in Cryptographic Extraction and Key Derivation: The HKDF ...
0
votes
1answer
85 views

In what cases will RSA not work? [duplicate]

I know that there are cases when RSA will not work like when the number to feed into the system is greater than the modulus. I was wondering if there were any other cases when RSA won't work I looked ...
2
votes
0answers
78 views

How to choose McEliece's parameters?

At the time of this writing, there are 3 sources for parameters for the McEliece public-key cryptosystem out there. The first paper is the original McEliece paper ("A Public-Key Cryptosystem based on ...
1
vote
1answer
42 views

Question on Miller's algorithm (change the input m)

From the book titled " An Introduction to Mathematical Cryptography" (Chapter 5,page 322), we know that the miller's algorithm returns a function $f_P$ whose divisor satisfies $$div(f_P) =m[P]-[mP]-(...
0
votes
2answers
522 views

What are the advantages of using OFB (Output Feedback Mode)? [closed]

I have a problem with OFB mode, because I have heard that it is stronger than CFB.
2
votes
1answer
69 views

Question about keyed hash functions

Maybe the answer to my question is obvious, but I have doubt... I have noticed that hash functions are studied in two forms, keyed hash functions or unkeyed. In general, lecture notes present hash ...

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