# All Questions

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### Major PKC data formats

I've been searching for various formats that encodes public-key cryptography keys and ciphergrams. Major PKC standards such as PKCS#1, SEC#1, and EESS#1 had been defining their data types as ...
11 views

### Prove: If there exist strong OWFs then there exist weak OWFs that aren't strong

Please help me to understand the proof of the following claim: Assume there exist strong OWFs, then there exist functions that are weak $\frac{2}{3}$-one-way functions, but not strong one-way ones ...
31 views

### hiding bits inside random bits, is this some sort of encryption?

Let's say that I uniformly sample a 1000 bits randomly. Then, I hide a secret of 10 bits on those 1000 bits, randomly. That is, I pick each of the 10 bits and randomly replace them inside the 1000 ...
28 views

### Complexity if there are more than one collision

Let $h: \{0,1\}^*$ → $\{0,1\}^l$ be a hash function. We define a k-collision as a set of k distinct messages in which $h(m_1)=h(m_2)=...=h(m_k)$ There is an attack running in time $O(2^l)$ which ...
27 views

### Where can I find good practice questions for proofs by reduction?

I already have the Katz-Lindell textbook, but I also want some additional practice problems for security reductions for stuff like PRFs, MACs, digital signatures, private and public key schemes, and ...
36 views

### Is SHA1 break significant for an algorithm intended to be Proof-Of-Work?

Let's say I'm modifying the Scrypt hash function (https://github.com/Tarsnap/scrypt/blob/master/lib/crypto/crypto_scrypt-ref.c) and that all I want to do is replace SHA256 with SHA1 in the code to ...
34 views

### Is it possible to have a shared secret without any party knowing all the parts?

I believe with Shamir’s Secret Sharing Scheme, I can create an n-part secret and distribute each of those parts to n parties. ...
104 views

### Can you identify these cryptographic algorithmic symbols?

I am mostly self taught and have limited knowledge of the symbology in the image below. It is a diagram of a sub block the RIPEMD-160 algorithm: Are such symbols standardized? Is there a good ...
36 views

### Is this kind of mutual Authentication safe?

The following is a real-world problem. In a standardized protocol clients can connect to a server using mutual 4-pass authentication on an otherwise unsecured TCP channel: pass-1: Client send random ...
26 views

### How to have a hash function that maps any binary string of size n to binary string of size n?

I am implementing certificateless cryptography from this research paper in python language. Essentially, I want to have the following hash function mapping. This hash function is mentioned in the ...
58 views

### Unable to factorise the modulus from public key to extract a private key

I have a public key but struggling to get the modulus from it ...
55 views

### Should I use HMAC to create a multiple part HASH token

I have a web API with a custom API authentication system that users each have a SecretKey and a public ApiKey. Using these two keys client(or user) can generate a token for the authentication on the ...
13 views

### SSH Server Configuration Best Practices? [migrated]

I hope this is the right place to post this. I have been tasked with reviewing the settings of an SSH server, I'm currently trying to figure out what are the best practices, and I'm having a bit of ...
186 views

### Timing attacks: Symmetric vs Asymmetric Algorithms

There is a statement that I can't give a reference; "Since the timing characteristics of symmetric algorithms are not as key dependent as asymmetric algorithms, they are more resistant against ...
31 views

### key reuse: does knowing H(S) reveal HMAC(S)

given a hash H() , like sha256 and a secret text S and a public salt P will knowing H(S) reveal HMAC(P, S) ? to clarify: the question is if it possible to learn the digest, not the secret. In my ...
31 views

### Cyclical Redundancy Check and bijections

Let $F_M(n)=\operatorname{CRC32}(M|n)$, where $M$ is an arbitrary length prefix message, $n$ is a 32 bit integer (whether little or big-endian encoded is unimportant) and "|" is simply ...
40 views

### Current research problems in Lattice based Crypto

I am looking for research problems in lattice based Crypto. Can anybody help?
212 views

### What is a function on a Line or a Curve?

I am reading up on Pairings using Elliptic curves & all the texts talk about functions on a Curve. I am finding it difficult to even figure out what they mean by "function on a curve" or ...
41 views

### Double encrypted cipher involving polybius square

I am trying to solve this cypher. I know that the cipher is double encrypted and that the second step is a Polybius square with the key of the letters of the alphabet in order from a - y. However I do ...
209 views

### Why are public keys derived from elliptic curve cryptography (ECC) and not from hashing?

I've just started studying Bitcoin and cryptocurrencies, so I might be wrong, but so far my understanding is that public keys are derived from private keys using ECDSA, in Bitcoin's case using ...
19 views

### Why I'm getting ValueError while trying to unpad the data? [closed]

In short, I'm developing an encrypted chat using ECDH + AES. All encrypting and decrypting algorithms work just fine when I'm testing them separately. They are also working when there is established ...
152 views

### Testing of PQC NIST round3 submissions

I am new to this field and have some concerns regarding PQC; How does NIST do a comparison that a particular algorithm is efficient and its security can not be broken by future quantum attacks? I am ...
68 views

### Is the base equally well protected by the discrete logarithm problem as the exponent?

I'd like to ask if in case of modular exponentiation, reverse engineering the base would be equally difficult, when knowing the exponent as determining the exponent is hard when the base is provided? ...
26 views

### AWS IoT - Unique Keys per each device - Data encryption

(Probably not the right board to ask. But here goes) I'm designing an IoT Solution with RPi as client and AWS as the server. On the client hardware, I have an Security Chip that can securely generate ...
79 views

### Can a series of attached tetrahedrons be used for cryptography?

(based on a prior question with triangle) Given a regular tetrahedron T1 (with his 4 vertices A,B,C,D lying in a finite Field $\mathbb F_N^3$ with $N$ a prime) another attached regular tetrahedron ...
26 views

### What is the difficulty_1 value of Bitcoin Gold? [closed]

I have searched an incredible amount of time on the internet looking for the base difficulty of Bitcoin Gold without any result. The difficulty of Bitcoin Gold at this point in time is 204460. I need ...
33 views

### Wireguard: How do I verify web traffic & would it be considered encrypted? [migrated]

I setup a connection between my Windows PC & a VitualBox Debian Server running WireGuard using this walkthrough. The connection appears to be working because the Windows WireGuard Client GUI shows ...
94 views

### Is there any fundamental difference between the block cipher operations encryption and decryption?

Is there any fundamental reason to designate one direction of a block cipher as "encryption" and the other "decryption"? Or are these arbitrary choices? Or perhaps practical ...
71 views

### what are security reductions of symmetric-key algorithms?

I was reading Wikipedia page of post-quantum cryptography. It says that it is desirable for cryptographic algorithms to be reducible to some particular mathematical problem, that is intractability of ...
66 views

### Bringing a key to 256 bit by a hash algorithm

For example, if I use Rijndael for encryption, I have to specify a key of a certain length. For user convenience, I want the user to be able to use a key of any length. Then, to get the key to the ...
943 views

### Any advantage to a block cipher which is not efficiently invertible?

The classic definition of a PRP includes efficient invertibility. Given that many modern cipher modes (CTR-based e.g. GCM) use only the forward direction of the block cipher, it seems that the ...
417 views

### Shamir secret sharing where some specific people are required to participate

By using SSSS we distribute the key to "N" people where any "k" (N>=k) are required to participate to unlock the code. But what if I wish to have the people "x" and &...
28 views

### What would you tell this string is? [closed]

I have found this string gyO0uqISbC7xThS/f7Wx5Q== but I'm not able to decode it. I've tried Base64, Rot13 and more things but nothing seems to be working. Thanks
50 views

### Why does CBC-MAC(M) = CFB-MAC(M)?

I don't understand why $\text{CBC-MAC}(M) = \text{CFB-MAC}(M)$. Has it something to do with $\text{CBC-MAC}(M) = C_L$ and $\text{CFB-MAC}(M) = E_K(C'_{L-1})$?
47 views

### Hashing function: Generate unique 3 letters Identifier [closed]

I need to create an id generation function that takes 4-digit number and returns a unique 3-letter identifier. I already have a function that generates a 2-letter id from 3-digit number with some ...
10 views

### Is it possible to use non-deterministic ECDSA signatures schemes for signing Ethereum transactions/messages? [migrated]

Is it possible to use a non-deterministic/probabilistic (choosing k randomly and not HMAC-derived from msgHash + privKey like RFC 6979 states) ECDSA signature scheme for Ethereum Signatures? If yes, ...
13 views

### How to use d2i_ECPrivateKey() to load my private key in c++ with openSSL [closed]

I'm trying to use d2i_ECPrivateKey() to load key from a std::string which contains my private key. My goal is to do the ECDSA signing. My code snippet. ...
60 views

### Homomorphic Encryption Library Supporting Addition, Multiplication & Logical Shift

Does anyone know of a C++ homomorphic encryption library that supports addition, multiplication and logical right shift over integers? Some set of instructions that allows the implementation of ...
40 views

### Number of Involuntory Keys in Permutation Cipher

I've came with the following problem from the Theory and Practice book by Stinson-Paterson. It states the following: 2.17 (a) Prove that a permutation $\pi$ in the Permutation Cipher is an ...
64 views

### Pretty much confused about pretty good privacy-:

Authentication-: I understand that authentication is basically digital signature. But what I don't understand is how it has been explained here specially the RSA key part. It is leading me to huge ...
34 views

### computation time of pairing operations and their securities

Suppose G1 is an elliptic group and G2 be a multiplicative group and they are of same prime order p and e is a bilinear pairing, e: G1 X G1 -> G2. The operations e(p,q)r and e(pr,q) gives equal ...
51 views

### Reverse SHA256 Hashed Value from Multiple Instances where Part of Hashed Value is known

I apologize in advance if this question has been answered already. However, I have not been able to find an existing answer - despite the case being pretty simple and common I imagine. Perhaps there ...
57 views

### Can attacker steal data from AES encrypted table without knowing the key?

I think of a situation that attacker can steal data from AES encrypted table without knowing the key. I tried to search on internet but found nothing about this(may be I were not using the correct ...
22 views

### Examples of oblivious transfer protocols secure under stronger security assumptions than semi-honest model?

The question is basically stated on the title. I have done some introductory reading on Oblivious Transfer and most of them are secure in the semi-honest model. Are there any protocols that are secure ...
24 views

### How to prove that paillier encryption is positive (zero-knowledge)?

Is it possible that the plaintext encrypted in a ciphertext using paillier encryption is positive without using a zero knowledge range proof?
28 views

### How to securely store data with an untrustworthy party?

Alice wants to store key:value pairs with Bob. The goal of the exercise is for Alice to be able to use Bob as a reliable data storage service, even if Bob were ...
45 views

### Short Nonces in ECDSA signature generation

Recently I noticed that my device generates short-sized Nonces. Approximately $2 ^ {243} - 2^{244}$. Could it turn out that there will be a small leak of ...
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### What does counter mean in Counter (CTR) Mode? Is it the same as nonce?

As asked above, what does "counter" mean exactly? Is it the same as nonce? Also, the book Network Security Essentials (6ed.) from William Stallings states, "Typically the counter is ...