# 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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### RSA - Is $e = d$ a problem?

I'm working on small RSA project in university. At this moment I have done this: An array of prime numbers is generated from selected range. $p$ and $q$ selected randomly from this array $n$ ...
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### Symmetric-keys algorithms with different keys for encryption and decryption

The Symmetric-key algorithm article from Wikipedia states: The keys may be identical or there may be a simple transformation to go between the two keys. I am not aware of any symmetric-key ...
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### Can I set certificate purpose in Android API 22? [closed]

In android api 22 I can use only this function to create keys and certificate: ...
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### Why a bulk encryption key and frequently used key needs to have a shorter lifetime?

In NIST standard (NIST SP800-57), the bulk data encryption key and other key material that is used frequently have a short lifetime. As quoted from (Sec. 5.3.6, point 6.b.): The originator-usage ...
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### How to calculate time needed for decryption of 64-bit key

I am having trouble figuring out how long it takes to decrypt a 64-bit key, given that a computer can do 1 billion trials per second. I know that there are $2^{64} = 1.844 \times 10^{19}$ possible ...
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### Key generation for DH key exchange - benefits of using KMI

Context We need to generate a key pair in order to perform DH key exchange with the other party. Some suggest to use a KMI solution (think: AWS KMS or like) in order to generate the key pair. ...
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### Can I compress $192$ byte key into $16$ or $32$ bytes which can be later used in KDF to recover full key

I have a key $k$ which is $192$ bytes long. Is there a secure way to first compress this key into $16$ or $32$ bytes, but in such a way that later given those $16$ ($32$) bytes I can use a key ...
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### Why should I export my private key instead of well known asymmetric crypto mechanism on openkeychain?

I'm trying to use password-store as password manager under linux. I created a private github repo with my gpg files in order to use it with other devices. I installed android-password-store app for ...
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### Good layperson analogy for password and encryption keys

NOTE: QUESTION UPDATED. SEE BOTTOM OF THIS POST. I'm writing something where I need to make someone come across as though they know cryptography. I don't know enough, but as cryptography plays only a ...
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### For the theoretic scenario of a brute force attack, how would you know if you succeeded?

That is something I never understood: If you managed to brute force an AES encrypted text, how would you know you cracked it? After every attempt, you wold have to compare the text to an English ...
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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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### What is the key generation and management process of a fully homomorphic encryption system?

I've been very interested in fully homomorphic encryption lately, and I understand the concept well enough, but there is one thing that I don't understand... What is the key creation and, more ...
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### How is the time intereval calculated for symmetric key re-negoatition in UK Security Standard ā Use of Cryptography?

According to point 10.6.4 (Encryption in Transit) in Security Standard āUse of Cryptography, one of the criteria for key renegotiation is timeout , Encrypted sessions MUST re-negotiate new symmetric ...
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### Looking for an algorithm to encrypt with a single key and decrypt with a lot of keys without consuming too much space

Is it possible to have an encryption scheme that could be encrypted with a particular key, then decrypted with a large amount of keys without massively inflating the size of the final result? I am ...
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### How to use separate keys for signing and encryption

I read that the same key should not be used for both certificate signing and encryption. I wonder if this is not a problem with PKI/TLS/SSL, the reason being asymmetric encryption is used to transmit ...
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### Encryption: am I doing it right?

I'm trying to get a per-user encryption key scheme off the ground and need some validation from wiser crypto pros. Consider the following procedure: User provides registration information to include ...
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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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### 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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### Cracking a key using a combination of partial keys

As part of a cryptanalytic attack I've carried out, I used a divide-and-conquer strategy to divide the secret key $k$ into several equal-sized partial keys $k = {k_1, k_2, ...}$. The attack works ...
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### What is the difference between key size and block size (for AES)?

We are working on AES and want to develop a website which should provide an encryption facility but we are not understanding the difference between key and the block size. More appropriately what does ...
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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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Assume that sender and recipient both already have each others public keys(certificates). Sender needs to generate session key to encrypt some data and sends encrypted data to recipient. All offline - ...
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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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### 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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### 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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### What is the main difference between a key, an IV and a nonce?

What are the main differences between a nonce, a key and an IV? Without any doubt the key should be kept secret. But what about the nonce and the IV? What's the main difference between them and their ...
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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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### 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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### 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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### How HSM stores keys securely

when we say that HSM stores keys securely we mean that non-authoriszed requester cannot access the keys. but the key is stored physically anyway in the hardware, so access is still possible if the ...
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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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### Revoke a GPG key using previously generated revoke certificate after renewd (change expiration date)

I have few sub-questions Do secret keys get expired, or just the public key gets expired? Do I have to back up the master sec key each time I renew it? For an ...
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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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### 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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### 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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### 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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### 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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### How to know the type of encryption method

If I have a program that take a string to give me the ciphertext, nothing stored, using the same keys. The ciphertext is a base64. Can I figure out the type of encryption by the amount of characters ...
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### Purpose of key evolution?

When generating and exchanging keys, what is the purpose of performing key evolution after public key exchange + authenticated encryption?
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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 ...