# All Questions

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### Dependence of a Pseudorandom Function's Security on its Input/Output Spaces

Let $n$ be a security parameter and $F:\{0,1\}^{\ell_{key}(n)} \times \{0,1\}^{\ell_{in}(n)} \rightarrow \{0,1\}^{\ell_{out}(n)}$ be a keyed function which forms a family of Pseudorandom Functions (...
24 views

### Are two halves of PBKDF output “related”

In other words, in the context of authenticated encryption using Encrypt-Then-MAC, is this stupid?: ...
17 views

### ECDHE Key with KDF Necessary

Is it necessary to pass a ECDH generated key to a KDF? According to the python cryptography documentation, it is stated that For most applications the shared_key should be passed to a key ...
25 views

### what is the motivation of multipartite secret sharing?

In this thesis chapter 3.1 [1] A multipartite secret sharing scheme is a scheme in which the set of participants is divided into several parts and all participants in the same part play an ...
27 views

### Bitcoin mining nonce and birthday attack

Having read the basics of mining and this about SHA256 (probabilistic?) partial preimage possible? and SAT solving - An alternative to brute force bitcoin mining, I have the following question: ...
15 views

### Should has the CMAC scheme the ECBC-MAC final block?

As I concerned the raw CBC-MAC scheme is not secure, and to solve this a final block using a different key is used. Also to fix the "Dummy blocks" generation for the padding in the CBC-MAC a CMAC ...
42 views

### collision resistance of a composed hash function

Given a collision-resistant hash function $H(x)$, and I device another hash function by $H'(x)=\sum^{m}_{1}H(x||i) \mod p$. The summation is defined on finite field of prime order $p$. Is the new ...
3 views

### How does windows 10 v.1803 save the password in the SAM file? [migrated]

I'm doing a search on how windows 10 saves hashed passwords in the SAM file. From this article I suppose that Windows does this: If the password is 123456 and the user has RID 000003E9: CALCULATION ...
20 views

The popular VeraCrypt encryption utility, as well as its precursor TrueCrypt, has the option to cascade multiple ciphers on top of each other, such as AES-Twofish-Serpent. It works by cascading three ...
2k views

### If hash functions append the length, why does length extension attack work?

I have understood that it's trivial to reconstruct the internal state of a hasher for many hash functions, if one only knows the output hash. Then, one can append data after the original data and ...
39 views

### It is the IV shared in CBC mode?

I don't know if the IV in CBC mode is equal in both sides of the encryption and decryption operations. I know that the IV must be unpredictable, but has it to be MACed in the encryption side to be ...
51 views

### What security is provided by a certificate? [on hold]

I've been working on the topic of certificates for a little while, and here is what I understand: A certificate is basically a public key + some data about the owner of the certificate + a signature ...
65 views

### On the security definitions

What are the differences between perfect security information-theoretic security semantic security indistinguishability are there other definitions? Do these security definitions depend on the ...
35 views

### How to encrypt an ASCII word using DES (ECB) [on hold]

I have a word, SIGURNOSTRACUNARSKIHSISTEMA, and my task is to find a value of a second block using initial permutation DES. Since this is more than 64-bit, I need to use ECB, but I have been unable to ...
46 views

### Point doubling with only one coordinate

In many source codes that implement ECDH, there is a function that multiplies the base point of that curve with a constant. This function usually takes as arguments the constant and just one ...
71 views

### How is the PRIVATE KEY actually created in the first place?

How is the "Private Key" created in the first place? I understand that once you have your wallet, you will also gain access to your public key and private key... But in order to have a wallet ...
16 views

### Why, in general, are proofs of possession (POPs) “clearly” not sufficient for substantiating the knowledge of secret key (KOSK) assumption?

In Ristenpart, Yilek - The Power of Proofs-of-Possession: Securing Multiparty Signatures against Rogue-Key Attacks they have the statement: In general, such proofs of possession (POPs) are clearly ...
81 views

### How many required known plaintexts for an attack are considered insecure?

I stumbled over this problem when looking at symmetrical block ciphers with a relatively small block size like 32 bit. When I was looking at more common block ciphers with a 64 bit, I learned that ...
26 views

### How to encrypt a small number of identities (which are related to each other)? / Which algorithm has the smallest bit-length?

I'm looking for an encryption with as small numbers as possible. Given a small group of identities ($G$) (e.g. numbers from $1$ to $N$). Given one entry (or a small number) $e_i$ allows to compute ...
88 views

### CVP over $Z_{q}$ - is the problem still hard?

I'm reading about the CVP problem, and all the papers I've read so far handle the case where the CVP matrix and vector are over $R^{n}$ (or over $Z^{n}$), and the distance is a real number. However, ...
49 views

### Are there any specific weaknesses in this crypto implementation?

I am reverse engineering the firmware of a particular router/modem. I am focusing on the functionality to export the router configuration. I an searching for a way to decrypt the configuration backup ...
32 views

### Are there any signature algorithms with pseudorandom signatures?

As the title says. My reference point for the "pseudorandom ciphertext" concept is this paper by Möller, which introduces a public-key encryption algorithm with this property. I want to know the ...
74 views

### How to sell a piece of data through blockchain?

User A attempts to sell a piece of data D (byte level) to user B at price C through the blockchain. A and B do not trust each other. A worry: After the data D is delivered, B does not complete the ...
126 views

### Are “non-mathematical” encryption algorithms comparably secure against brute force key recovery?

I recently learned about a desktop encryption application called ALKEMI, which does not use mathematical encryption according to the website, which I understand to be a misnomer, at best: The ...
2k views

### Does a hash function have a Upper bound on input length?

I came across this Answer stating (just a line from the answer):- The input space is "infinite" and thus it has an infinite amount of values that will collide into a single hash And in the ...
44 views

### Securely rekey/re-encrypt AES-encrypted file

Suppose I have a big file encrypted using AES (any mode you want) with key kA. I'd like to give an untrusted proxy a kA->kB "conversion key" so that it re-encodes ...
45 views

### Do q-ary lattices have parallelogram kind of structure?

An $m$-dimensional lattice is defined by a basis $A \in \mathbb{R}^{m \times n}$ is the set of points $\{Az : z \in \mathbb{Z}^n\}$. A picture of these points would be like a nice parallelogram kind ...
25 views

### Data Integrity check on IoT systems [on hold]

Sending a signed file from Onsite datacenter to IoT(box) or Linux box using any HSM Linux box will have a signed public key to verify the integrity. We should be able to generate the key pair on any ...
46 views

### How to calculate M when the attacker know e and w

Alice has a pair of RSA keys, the public key is $(n,e)$, the clear text message $M$ and the ciphertext $C=M^e \pmod n$. We suppose that Bob wants to encrypt two successive messages and send them to ...
28 views

### Fully homomorphic encryption - modulus switching technique [on hold]

How to implement modulus switching technique to reduce noise in fully homomorphic encryption scheme?
8 views

### NIST Randomess Test Running [migrated]

I am trying to run NIST randomness testing on an Input file having 3645018 bits. I can see that it's giving correct frequencies of Zero's and One's but I am not able to get the results of other test. ...
20 views

### Question about publication “Efficient (k,n) Threshold Secret Sharing Schemes Secure Against Cheating from n − 1 Cheaters”

In the paper on section "4 Proposed Scheme", I suppose that the scheme does not protect if an adversary has access to the $k - 1$ original shares, am I correct? If the adversary has $k - 1$ of both ...
31 views

### Whether ramp secret sharing possess additive homomorphism?

Ramp secret sharing replaces the random coefficients in original Shamir secret sharing with original data to be shared. In such a case, all the coefficients in the polynomial evaluation will be ...
28 views

### Public Key VS Wallet Address - What is the difference? [migrated]

I am seeing a lot of contradictory information on why we now use Wallet Addresses rather than Public Keys. Some say that due to additional level of hashing (double hashing), Wallet addresses are ...
71 views

### Does larger key size mean larger data size in asymmetric encryption?

I'm new to cryptography. I know the larger the key size (like 128-bit vs 1024-bit) the harder the ciphertext is to crack, generally. But assuming everything else being equal, does a larger key size ...
42 views

### Asymmetric Encryption - How is the Public Key Being Shared?

I've been reading up on the relationship between private keys and public keys (as well as hashing), and I watched a few videos, but I am still a bit confused. I don't have a programming background, ...
29 views

### How to accept USDT payments the right way? [migrated]

We are developing an e-commerce solution and consider USDT to accept payments. At the moment as I understand we can generate many addresses (1 per transaction) with BIP32 spec approach. Based on Omni ...
38 views

### pseudorandom permutation [on hold]

Assume that $F:\{0,1\}^{\lambda}\times \{0,1\}^{\lambda}\longrightarrow \{0,1\}^{\lambda}$ is a pseudorandom permutation. How to prove give two different pair $(k_{1},m_{1})$ and $(k_{2},m_{2})$, the ...
28 views

### I was to send signed file to IoT system. How do I use PKI for this [on hold]

I was to send the signed file to the IoT system. How do I use PKI for this? I require to store a private key in HSM.
42 views

### Security of ciphersuite and key

Is anyone able to cite resources that can be based on choosing a cipher suite? In my case, for a VPN server (OpenVPN) I chose a set of ciphers: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 It provides 128 ...
25 views

### Generating Public Key For ECDH with Botan (C++) [closed]

I am trying to implement ECDH with Botan by using C++. First, I generated two private keys. Yet, I could not handle to make it for public keys. Botan::AutoSeeded_RNG rng; // ec domain and Botan::...
148 views

### Difference between Pure EdDSA (ed25519) and HashEdDSA (ed25519ph)

My question refers to EdDSA as specified in RFC 8032. I get from the RFC that ed25519 and ed25519ph are two different instances of EdDSA mainly differing in the fact that that in the case of ...
44 views

### AES-256 Encryption 111 [closed]

In the Guarda cryptograph, the password was lost. There is a backup file backup.txt in which the keys are encrypted via AES-256. How to decipher?
34 views

Is there a program that automatically inserts the password options in the login field (as long as it selects the right one) using the search method and with the condition of approximate password data ...
34 views

### Nomenclature of Certificate Authorities and Certificates in PKI

In PKI there are different terms to identify certificate authorities in the chains. All terms I know of are as follow: Root Subordinate Super Intermediate I see all terms used interchangeably in the ...
23 views

### How to handle multiple key-agreements

If I would use two different key-agreements e.g. SIDH and ECDH how would I handle these both derived keys? Is there a different between XOR or SHA-256 the two keys? (Would one reduce the level of ...
2k views

### Can error correction and detection be done without adding extra bits?

I have gone through error detection and correction techniques like Hamming codes, and BCH codes require extra parity bits for detection and correction. While sending data, we always seem to introduce ...
74 views

### Difference between hash functions and algorithms?

Wikipedia lists "Hash function algorithms" within the "Hash function" page. I'm wondering what are the differences and if I can use the terms "hash(ing?) algorithm" and "hash function" interchangeably....