Questions tagged [keys]

Private and secret keys consists of secret information used as input to various kinds of cryptographic algorithms such as encryption, signature and MAC to select the concrete transformation done by the algorithm.

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Is there any cryptographic scheme with block size more than 128 bit

I am asking this question out of curiosity if there are any cryptographic algorithm that has a block length more that 128 bit. I am new to cryptography and I didn't know any. AES 128, 192, 256 all ...
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With RSA or ECC, if I encrypt my private key with my public key, is there a way to recover my private key?

Is there an algorithmic, mathematical, technical or implementation "hack" to recover the private key or is it definitively encrypted without any particular mathematical property, like any ...
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Are the asymmetric roles of the two keys in the elliptical curves the same (as for RSA)? Can they be interchanged indifferently?

More precisely, and as for RSA, is it really true that it is not feasible to recirculate one of the keys knowing ONLY the other with the Elliptic Curves, as for RSA? Or does ECs work differently on ...
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Key generation times vs CPU load

Does the key generation time affect the CPU load in a mobile phone, an embedded device? I am searching on Google for info, but I am not fully sure that I have concluded to something.
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Same private key for signing and decryption

I am designing a service which identifies records with public keys. All other fields are encrypted with that public key and protected by a HMAC. For authentication, I am thinking about signing ...
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Generating a XOR Hash function for a given group of numbers to maximise collisions

Given $x$, a vector of $m$ distinct bit vectors of bit length $N$, I want to use an XOR-hash $h$ such that all $x_i$ collide to the same value. I define an XOR hash $h$ which takes bit vector $q$ as ...
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Generating a recovery phrase for a RSA key-pair

What is an optimal way to associate a RSA key-pair with a recovery phrase/seed for access recovery purposes? I've seen a lot of cryptocurrency wallets provide this feature, however, I'm not looking to ...
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Is choosing $1$ as a public exponent valid in RSA?

I know it will not encrypt anything. But is $1$ valid as a public exponent in an RSA public key?
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RCON for AES 192 and 256

This is question about how many RCON values are used in AES 192 and 256. I read the NIST Publication introducing AES and in Appendix A.2 and A.3 (Key Expansion for 192 and 256-bit keys), only $rcon_1$ ...
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Are skeleton keys possible for ECCDSA?

As alluded to here (split-key vanity addresses for bitcoin), ECCDSA-keys can be merged such that the sum of two private keys $S=S_1+S_2$ yields a public key which is the sum of the respective public ...
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Curve25519 key structure

In the paper regarding Curve25519, the set of public keys $q$ is $\{q : q\in \{ 0,1,2,...,2^{256} - 1\}\}$ and the set of private keys $n$ is $\{n : n\in 2^{254} + 8 \cdot \{ 0,1,2,...,2^{251} - 1\}\}$...
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RNG to hide some bits

Suppose I have a sequence of bits of length M. I need to hide N out of M bits (hiding means forcing them to be 0) using RNG with a key. How I can relate the output of RNG to the number and positions ...
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What kind of approach can I use to reverse the following encryption scheme?

I'm trying to reverse an encryption scheme without success. I have several pairs of ciphertext + plaintext and found the encryption method to be something like this: ...
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Symmetric algorithm effective key length

If we have a symmetric algorithm with key length $m$ bit, and we do a 5 time encryption with it. How much will it be its effective key length.
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Does my encryption scheme make sense?

I'm looking at a way to encrypt a file so that our software will only allow users with the proper license to use it (see details below). I have some notions on that topic, but barely more than knowing ...
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Prove how to brute-force the double encryption with complexity 2^57 rather than 2^112?

We know that DES has key length that is too short to defend brute-force attack. One idea to improve DES was to encrypt a message using DES twice with two different keys. Let E be the encryption ...
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PIN & PUK protection for key

I'm trying to protect a key using a PIN code. However, if the user somehow loses the PIN code, I'd like to be able to allow recovery using a PUK (similar behaviour as for instance your SIM card on ...
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Encryption and decryption with Diffie-Hellman

I don't understand how it works. I only found explanations about the key exchange, but what about the actual encryption and decryption? Do you use the session key $K$ with a symmetric algorithm? Do ...
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Does a cipher exist with the following properties?

The key can unlock the ciphertext in polytime (measured in length of key + cipher). a. Given the key + ciphertext as input, if you cannot unlock it in some fixed number of steps (relative to input ...
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Number of keystreams generated in Kreyvium for a single key/IV pair

Kreyvium employs 128-bit key and 128-bit IV. By a single initialization procedure using a key/IV pair, how many keystreams can be generated?
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Are My Answers to This AES Question Correct?

Question I am extremely new to cryptography and AES and so I am not confident that I did this question orrectly. Please can you check my answers and let me know if anything jumps out as incorrect, ...
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Is it okay to reuse a single symmetric key for a large volume of messages and HMACs, so long as “nonces” are randomly generated for both of them?

https://www.reddit.com/r/crypto/comments/fnku50/nonce_reuse_vs_iv_reuse/ Nonce reuse with the same key is catastrophic to security. The same premise holds for initialization vectors. If the key ...
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Secret key formed by the combination of several keys

I think there exists an algorithm to create a key from the combination of a group of keys in such a way that if I encrypt a message using the key formed from the combination, I should be able to ...
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Encrypt files on harddrive with double encryption

So I've been stuck on this question for a very long time. How do you use double encryption to encrypt a hard disk so that all of the following conditions are met: All data on the hard disk is ...
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Is it possible to find the key of an HMAC-SHA-512 given the input and the hash output?

Is it possible to find the key of an HMAC-SHA-512 given the input and the hash output? If so, what algorithm if any prevents this? I'm working on a simple E2E communication system between two self-...
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Proof of probability of weak keys in block cipher

My textbook has the following theorem: Given a block cipher with a key length of K bits and blocksize of n bits as well as t plaintext-ciphertext pairs, the expected number of false keys which ...
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Is it possible to sign an Android OTA Zip using Hardware Security Module protected keys?

In my scenario, the ‘Release’ private key that matches the .pem cert file is stored in a HSM and it’s non-exportable. I see that signapk.jar takes the -providerClass parameter (which in theory should ...
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What measures can I do to prevent decryption of encrypted data?

This is entirely hypothetical, I'm working on securing some data and I want to make sure we do this properly. If I have a list of information which is encrypted (say, using a 256 bit encryption key) ...
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Can MFA codes be predicted if you know what their values were at a previous time?

I use an app on my phone that, after scanning a QR code on a website, gives me 6-digit codes which change every 30 seconds. These codes can be used for Multi-Factor Authentication (MFA) on some ...
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Protect student log data through public-key encryption and a trustee

I am looking for an GDPR-conform way to log student behavior in an online learning system (Moodle). In the system, students are offered a course to be examined in a field study. According to the GDPR, ...
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Best method for storing cryptographic secret key and generation of IV in Trivium?

How the secret key for Trivium cipher is stored and managed in an embedded system (IoT sensor node)? How the IV is generated in a Trivium? How to justify the fact that storing a fixed value (for ...
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Does pepper *require* an HMAC?

Assume you are already given a properly-salted, password hash $X$ from some slow PBKDF (e.g., like Argon2id). Now, you want to apply some large (~256-bit) secret "pepper" $S$ to it before storing it ...
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What kind of attack would a 128 bit SHA-2 be vulnerable to and why?

With SHA-2 for hashing, using only the first 128 bits to create a 128 bit hash, what kind of attack would this be vulnerable to and why? Since 128 bit encryption keys are secure, shouldn't a 128 bit ...
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KRACK - Is all-zero key installed by the acces point?

I don't really understand (and I think it's not described in the official paper) how the encryption can work when the encryption key is set to 0 by a KRACK attack on a device using wpa_supplicant 2.4 ...
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Disk storage of RSA and DSA keys

I have generated one RSA-2048 signing key and one DSA-2048 signing key, using gpg command gpg --full-generate-keys I would expect the key to have size 2048 bits, ...
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Prove linkage between secret keys

Hey guys I'm not a crypto expert so apologies if the question is especially noobish. We have a web application that requires the user to sign certain messages. We have been storing the secret key in ...
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Motivation for frequent key updates

I am wondering if there is any reason to regularly update cryptographic keys, that are used for authentication purposes in a real-time system. A key should be updated if it is weak, broken, ...
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How to calculate new AES keys for NFC application?

I want to program a couple of AES-enabled NFC tags (for example these) with some custom data, and secure these tags by using the AES features of said tags . In order to increase security, i want to ...
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Encrypting Data with user + custodian private keys

I want to be able to have a private user key (system generated) which, if destroyed, effectively renders all user data unrecoverable. This key would be used across the entire system to protect the ...
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Perfectly secure cryptosystem as many keys as plaintexts

Is a cryptosystem perfectly secure if there are at least as many keys as there are plaintexts? My guess is yes but I am not sure, new to cyptosystems
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Storing public key in cookie

I am encrypting my password before sending to my server with a public that i have stored as a cookie. Is there any security risks storing my public key in the cookie? Are there any better ...
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Prove that for key with $n$ dimensions, the order of the key is $k!$

I need to prove, that for a key with $n$ dimensions, they order of the key would be $n!$ and to prove that, I need to use mathematical induction: $$\text{Let n = 1} \Rightarrow {1} \text{ if there ...
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Trying to understand how the same secret key end up being calculated between Alice and Bob

This is basically a duplicate of this question which was not answered very clearly. From the documentation, these are the calculations that happen for Alice to compute the shared secret key: ...
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PCI - Limit Key Injection Capabiltiy 3DES + DUKPT

Current Context: I'm using a Triple DES with a DUKPT Key Management Approach. I have two organization which have access to the BDK Key: Orgzanization 1 which acts as the Secure Decryption ...
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Key Exchange vs Key Encapsulation

From what I understand, the steps of a key exchange protocol are Alice and Bob each encrypt something using their public key and private key and send the result to each other Alice and Bob each do ...
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BIP32 Extended Key to EC Private and Public Key Pair

We are working on an application in Android using Java. In our project, we used to generate EC key pairs (of size 384 bits) using SpongyCastle - an old Android version of Bouncy Castle. The problem ...
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Computing PGP ed25519 and curve25519 keygrips?

There are public key algorithmic differences for how PGP computes fingerprints and keygrips. For the v4 protocol, fingerprints are not exclusively computed from public keys while keygrips are. RFC ...
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AES key with DES3_CBC_PAD mechainsm

I am new to cryptography and have a question. If I try to wrap some key using an AES key using DES3_CBC_PAD as a wrapping mechanism will this go to work? I am doing this operation inside an HSM.
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RSA p and q size to encipher a block

I have a plaintext about 18 bit size. I have to encipher it using RSA. How large have to be p and q? So M (message to encipher) = 2**18 bit I tried, using a Python coded RSA alghoritm, different sizes ...
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Why is the Keyspace of a Substitution Cipher not 2^26 but 2^88

It is known that a cipher has a keyspace of cryptographic algorithm whose key length is $n$ is given by $2^n$, but the keyspace of the substitution cipher is $2^{88}$ which is an approximation of $26!$...

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