# All Questions

19,143 questions
2answers
54 views

### SIDH cryptosystem question

I'm trying to understand the SIDH cryptosystem and got confused at this point: Alice fixes base $\{P_A,Q_A\}$ so that it generates $E_0[l_A^{e_A}]$. Then she chooses secret parameters $m_A,n_A$ and ...
2answers
78 views

### What are linear and non-linear elements in cryptography?

I was reading this answer, How secure is XOR for encryption, and it stated that XOR's aren't good for securing messages as they are linear in Nature. And therefore should be paired with some non-...
0answers
21 views

### Difference between RSA & ECC [duplicate]

My question is regarding Asymmetric-key encryption, in which situation is better to use RSA? What are the advantages of RSA comparison with ECC but from a security point of view? Thank you
5answers
4k views

### Is the decompression of compressed and encrypted data without decryption also theoretically impossible?

We have two communication points in an information system, call them A(lice) and B(ackup). B has to store encrypted data received from A. The storage of B is encrypted, but not compressed1. B should ...
1answer
96 views

### Could time lock encryption be implemented through indistinguishable obfuscation?

In the paper "How to build time-lock encryption", the authors give a theoretical solution to build time-lock encryption using multi-linear based witness encryption and blockchain. However, an ...
2answers
53 views

### Efficient attack on RSA with known padding scheme and public key

I am having some trouble with an assignment problem. I hope I can get some guidance here. The question provides us with a public key, $N$ and the padding scheme. This is the padding scheme "Assume ...
1answer
40 views

### NIST elliptic curves behaving anamolous in OPENSSL benchmark

I tried to collect some benchmarks on NIST elliptic curves using charm library. The charm library is just a wrapper over OPENSSL. I experimented with prime192v1 (P-192), secp224r1 (P-224), prime256v1 (...
1answer
34 views

### Naming convention for NIST elliptic curves in OPENSSL

NIST standardized 5 elliptic curves (P-192, P-224, P-256, P-384, P-521) for prime fields. When I looked into openssl, these curves are named as prime192v1, secp224r1, prime256v1, secp384r1, secp521r1. ...
1answer
170 views

### What information does $g^x$ reveal about $x$?

Let $p$ be a large prime number. Let $G$ be a subgroup of $\mathbb{Z}_p^*$ with order $q$ - again a large prime. Let $g$ be a generator of $G$. Consider the following standard protocol for ...
0answers
32 views

### Strong and Practical Hand Ciphers [duplicate]

I know monoalphabetic ciphers are weak, but my message recipient doesn't like taking the time for the decryption process. I've tried Vigenere, Gronsfeld, Beaufort and Digraphic Ciphers, but he doesn't ...
2answers
62 views

### Distinguishing Original VS Fake Products

Let's assume that we want to distinguish original vs fake products when a customer receives them. I was thinking about using a protocol similar to digital signature. My question is can this problem ...
0answers
33 views

### How “Resending Message Attack” works?

In the second chapter of Bruce Schneier's book Applied Cryptography, 2nd Edition, 1996, we find this in section 2.7.1 Resending the Message as a Receipt: ...
0answers
4 views

### AWS cloudHSM ECDSA-SHA256 signature output to DER [migrated]

I am attempting to use an AWS cloudHSM to sign a message that needs to be converted to DER to be verified by another application. The output signature file from AWS is binary and I am struggling to ...
1answer
59 views

### Where can I find test vectors for the present cipher with a 128-bit key?

Where can I find the test vectors for the present block cipher with a 128-bit key?
1answer
2k views

### Cryptography and patents

First of all, I've seen a question marked as off topic because OP doesn't cover any issue related to cryptographic work, but the legal aspects, but I'm unsure where to attend to ask the following ...
0answers
36 views

### From 2-round key-exchange protocol to a public-key encryption scheme CPA-secure

I have to solve this exercise and I really could use some help: Show that any 2-round key-exchange protocol (that is, where each party sends a single message) satisfying $Definition$ $9.1$ can be ...
0answers
62 views

### How to prove that a predicate is not hard-core?

How can I prove that given a predicate $hc$ and a one-way function $f$ that $hc$ is not hard-core? I was thinking about something like that: i define $f(x) = (g(x), hc(x))$ that is one-way but $hc$ ...
1answer
25 views

### Estimating difficulty of “Memory-Hard Proof-of-Work” based on “size of memory”?

In Bitcoin proof-of-work, the difficulty of Proof-of-Work is estimated and calculated based on total hashing power of the participants. If total hashing power of the participants is higher, then PoW ...
0answers
18 views

### Looking for commutative asymmetric cipher for data matching

I need some crypto operation for matching data privately between two peers (let say Alice and Bob). Alice should be able to encrypt her data with Alice and Bob public keys and pass the cipher text to ...
0answers
22 views

### Test Vectors for XEdDSA

Anyone aware of test vectors (preferably with intermediate values) for the XEdDSA algorithm?
0answers
35 views

### Finding the period of a function with a single output qubit - impact on RSA

In this paper,May and Schlieper claim that one can find the period of a function $f()$ by embedding $h \circ f = h(f(x))$ for input $x$. This would have the immediate consequence of reducing the ...
2answers
124 views

### Does ChaCha20/Salsa have the same Bit Strength as AES for identical key sizes?

i.e. does ChaCha20 with a 128bit key, require 2^128 attempts to brute force, as with AES-128, theoretically? Ps. notwithstanding that ChaCha is a stream cipher.
1answer
74 views

### Symmetric property of DDT of inverse function

Given a bijective function $F: \mathbb{F}_2^n \rightarrow \mathbb{F}_2^n$. The entry of the Difference Distribution Table (DDT) at row $\alpha$ and column $\beta$ is defined as DDT_{F}(\alpha,\...
1answer
63 views

0answers
60 views

### Does such cryptographic scheme exists?

Is there any multi-key additive homomorphic encryption scheme based on elliptic curve cryptography? Meaning adding encrypted values encrypted with different public keys and decrypt the total sum with ...
1answer
34 views

### Why create a subkey in the digital signature algorithm

In the signing step, wikipedia, a subkey is created. A key k is randomly chosen from 1..q-1. What's the use of that k? If the k is to make less exposure to the ...
1answer
72 views

### Entity authentication protocol by encryption

I'm not a cryptography expert, so excuse me if the question seems very trivial. I need to know if this protocol is secure against a MiTM attacks and ensure a safe entity authentication method. We ...
0answers
77 views

### Security of an Elliptic Curve Public Key with a “Small” x-coordinate

Consider an elliptic curve over a finite field $F_p$ with $p$ prime and order $n$. Let $Q$ be a generator for the field. Given a public key point $P = aQ$, suppose we have an algorithm that finds an ...
0answers
45 views

### Is there a public-key system that can chain?

Does there exist any asymmetric cryptosystem that has the following properties: If I know somebody's public key PBK_1 and my own key pair (PVK_2,PBK_2), I can construct a new public key PBK_3 such ...
1answer
35 views

### Key exchange without an underlying semigroup

I am wondering whether there is a general reformulation of perfect forward secrecy for 2 party key exchange in 2 messages using semigroups. I am looking for references, which would discuss such ...
1answer
98 views

### Does such a cryptographic protocol exist?

Persons A, B and C put x€, y€ and z€ in a pot, respectively. Suppose that anyone can make a withdrawal from the pot as long as they prove they have such a right and that the y€ that B deposited is ...
1answer
3k views

### How long does it take to crack RSA 1024 with a PC?

Using an Intel Core i5 CPU, how long does it take to crack RSA using a key size of 1024 bit (generated using a secure key pair generation function)? Suppose for instance that we have thousands of ...

15 30 50 per page