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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 battery usage an important parameter for mobile based key exchange protocol?

I am studying a key exchange protocol based on public key cryptography technique specifically designed for mobile devices. I noticed there is no importance given to battery usage by these protocols. ...
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610 views

How to properly AES encrypt a string, deriving the key from the same string?

Let's say someone has a list of names, e.g.: 'Batman' 'Batman' 'Super Man' I am auditing this list, but I'm not allowed full access to all names. So they must be ...
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105 views

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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273 views

How to securely combine multiple sources of entropy?

Suppose that I have $n$ secure 32-bit keys that were generated separately using methods that are known to be secure. For example, one of them might have been generated by using a proven CSPRNG. ...
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3answers
941 views

Derive a key from a password and another key?

I would like to encrypt some data using a password. I want to use a function like PBKDF2 to turn my password into a key. However, I would like to also require a keyfile, for added security. My data ...
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911 views

Is including the key as AAD actually dangerous?

In a recent answer, Maarten mentioned including the key is a bad idea as well. This got my curious. Is there any scientific / cryptographic analysis whether including the key in the ...
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242 views

DES Subkeys in one box?

Can one calc the 16 subkeys in DES in one step ? I mean that we create for example a new “box“ where we directly permute the key k in 16 subkeys
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1answer
306 views

Use Cases of Otway Rees key exchange protocol

I am working on an seminar paper regarding key exchange protocols. Of course my first choice of protocol was DH. Second, I choose Otway Rees protocol since I found it very interesting that there is ...
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148 views

Handling key invalidation

I'm writing an Android app which will need to store some data for the user as a byte array of unknown length. The data must be encrypted. I have gone down the path of the hardware-backed keystore and ...
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1answer
179 views

Explain the mathematical definition of a cryptosystem using words

So when googling "cryptosystem" I found a Wikipedia page which contained a mathematical definition of a cryptosystem. Find this definition below. Could someone tell me what that what the last line ...
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1answer
280 views

Speeding up the Denning-Sacco protocol?

I have started to study cryptography and I have come across Denning-Sacco protocol. I understand multiplicity vulnerability. My question is why Denning-Sacco protocol choose to generate key on ...
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258 views

What are the costs of generating master key for symmetric ciphers?

I recently read that generating large master keys for symmetric ciphers is very expensive. But what exactly do they cost? Any references would be much appreciated. I have checked NIST but actual costs ...
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1answer
694 views

Why does appending a message to a key before hashing not guarantee integrity? [duplicate]

I want to guarantee the integrity of a message $m$. My first thought is to append the message to an integrity key $k$ and hash it as $H(k\,||\,m)$. However, I have been told that this is not totally ...
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51 views

Trying multiple private keys against a pcap

I have 1000's of Private Key files "f0167f3d025582d6bb65d5ca501a50eb.key" etc to use against a PCAP file. Only one of those private keys are valid and I am wondering what would be the easiest way to ...
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2answers
79 views

Why should keys be hidden from an eavesdropper for a pseudorandom function?

What advantage would knowing the key used for a given pseudorandom function give over having access to an oracle for that function $F_k(\cdot)$ and the actual key $k$ which will be used? Thanks very ...
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465 views

How can I find or reverse engineer the whitening in an AES algorithm?

I am working with this black box cryptography scheme. I know the plain text, cipher text, and everything else except how they whiten the data (or key?). Everything is 128 bit, 16 bytes. I have two ...
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2answers
9k views

Key derivation functions (KDF): What are? Main purposes? How can they be used?

What are KDFs? What are their main purposes? How they can be used, in other words, what's their drill in a cryptography scheme?
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156 views

General idea for storing public/private keys?

What are the general ideas for storing keys in order to make sure no one else has access to it? It's not a good approach to hash the keys, since you are going to need them later.
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What is the use of key iterations?

I read about PBKDF2 on Wikipedia and seen few apps. having option to manually enter number of iterations. I am still not clear on this. (1) With what I understood, key iterations can be used only ...
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1answer
731 views

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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1answer
70 views

Can you type your own keys?

Instead of generating keys, is it possible to type your own? For example, could all the characters be A's for example sake. Or do they have to be generated because they are based off of prime numbers ...
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1answer
2k views

What's the difference between DH and DHE?

The DH equation is: $$ K = g^{xy} \bmod p$$ Does using DHE mean even the $g$ and $p$ parameters are randomly generated (instead of being fixed)? Is this the difference?
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4k views

How does the sender obtain the receiver's public key?

Cryptography process includes encryption and decryption process. In public key cryptography public key of receiver is being used for encryption. I want to know how public key of receiver is sent to ...
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449 views

Guidelines for cryptographic key generation

I was wondering whether you know can point me to some general (basic) principles/guidelines one should follow for generating cryptographic keys? I have looked at NIST 800-133, but was hoping for some ...
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1answer
169 views

Can encrypting well known files hurt the security of the key?

I wanted to know if mass encrypting files (both well known and not so well known) on my external HDD would somehow hurt the security of my private key. As for the details: I am using GPG with a key ...
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1answer
279 views

Selecting an appropriate key for HMAC

I'm writing a symmetric encryption scheme for a product that I'm working on which doesn't store sensitive data (license validation data). I'd still rather do it right and reuse it than do it wrong and ...
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303 views

Detection of weak keys for AES-GCM

There are many papers out there that show that a message authenticated and encrypted by AES-GCM can be forged if the used key is weak (e.g. by Handschuh and Preneel, Saarinen or Procter and Cid). With ...
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40 views

How measurement error works in PRNG operation?

Suppose, I have PRNG with seed key length of $|K_s|$ and output sequence length of $2^{|K_s|}$, so the complexity of the PRNG is of the order of $2^{|K_s|}$. Now, if there is any measurement error in ...
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207 views

Is this method of string encrypting “uncrackable”?

I was thinking of unique methods of encrypting strings, and I thought of this. Given a string, for example "Hello, World!" we can convert it into a char array using a computer program, and then ...
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1answer
382 views

Is it safe to send HMAC and plaintext in the same message?

If a certain protocol sends $plaintext$ and its corresponding HMAC then is such a protocol prone to key extraction attacks ? Intuitively , HMAC is $ciphertext$ generated from $plaintext$, (although ...
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1answer
355 views

Probability of same input as output in AES 256

Note: I am assuming that, when entering in the key and plaintext, they are formatted in the same manner as the output of an AES-256 encrypted text. What is the probability, if any, that you could ...
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2answers
387 views

Using hash functions for Key Check Values (KCV)

As discussed in this post, calculating key check values for block cipher keys can introduce vulnerabilites. Plus, this method only applies for block ciphers, and there is no equivalence for private ...
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Clarification on Size of an Encryption Key

Given a key with a certain key size (e.g., 64bits). Would I be correct to interpret this as 8 characters (since each character would be 8 bits under ASCII encoding)? Because the ASCII scheme is ...
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119 views

How to choose key from string?

do you know any methods for choosing specific position in text for a key? Background: Lets suppose, that I want to encode message to friend: Text1 (not too long - max 1000 chars). I have made ...
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1answer
603 views

AES Key Generation based on database guid

I am developing a .NET application spanning multiple servers who should all be able to decrypt data stored in a SQL database. My database is multi-company where each company has its own GUID. since ...
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2answers
217 views

MAC unforgeability and secret key guessing

The standard notion security for MACs is usually expressed by means of experiments like the following one (given an attacker A): $k \leftarrow \mathsf{KG}(1^\lambda)$ Invoke $A^{\mathsf{TAG}_k(\cdot)...
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209 views

Chance of finding the right key by exhaustively searching on half of the key space

An exhaustive search of half the key space requires $2^{n-1}$ work and provides the right answer 75% of the time. If the attacker finds the key, he knows the answer. If he doesn't find the key, he ...
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490 views

Do all ciphers have equivalent decryption keys?

Do all ciphers suffer from the problem of multiple equivalent decryption keys? Is the existence of equivalent keys an essential property for the security of a cipher? If you could prove that a cipher ...
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353 views

Questions about length key of RSA 2048 bit

I use putty gen to generate RSA key, I choose length of key is 2048 bit, it generate public key: ...
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1answer
2k views

How can I obtain the raw decimal value of an RSA key's modulus? [closed]

So maybe I'm thinking about this too hard, or maybe I'm missing a piece of information. We'll use Google for this example. Say I wanted to obtain the modulus of Google's current public key. Well I ...
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Truly Random Values [duplicate]

I am trying to build a one-time pad encryption software and I am thinking about simply using /dev/random to generate keys. My question is: Is it ...
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1answer
126 views

Highest prime factor that is Safe for a particular scheme

My question is how many bits of prime number is secure so that it cannot be factored from very large number? Until today how large prime factor is found in large number? Quantum computing find ...
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1answer
118 views

Need help understanding this exercise's solution

We were given this exercise, which asks us to identify the types of keys used on this diagram: The solution was Kxa -> A's private key Kya -> A's public key KxB -> B's private key My question is, ...
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347 views

Is there a administrator key that can decrypt all ciphertexts encrypted with different keys by different persons in a group?

here is the scenario: $A, B, C, \ldots, Z$ are in a group with a administrator $Admin$, each of the users in the group has his own key $Key_A, Key_B$, and so on... everyone encrypt his own ...
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1answer
139 views

Can you decrypt with 1 round key?

If one has the last round key in an SP or Feistel network (the 16th round key in DES for example), would that someone be able to decrypt the rest of the encryption?
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1answer
102 views

Master keys' strengh

If I am going to use a master key to generate a session key, why the master key must be "stronger" than the session key? Like should not be distributing 128-bit AES keys derived from a 56-bit DES key....
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1answer
102 views

Use MDC to provide origin authentication for public key encryption?

Why can't we use an MDC (“Manipulation Detection Code”, as also handled in this Q&A) to provide origin authentication when using public-key encryption?
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12k views

Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy ...
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423 views

Do I need to worry about timing attacks in Base64 encoding/decoding of private keys?

Do I need to worry about timing attacks in Base64 encoding/decoding of private keys? This is a common operation (ex. PEM keys) and is variable time in typical implementations.
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5k views

How long should a HMAC cryptographic key be?

In the top answer to this question the answerer says 'with a sufficently long key'. I am using a SHA1-HMAC (may switch to SHA256-HMAC) algorithm to verify cookies sent to clients as authentication ...