usually secret information used as input to various kinds of cryptographic algorithms, like encryption, signature, MAC, to select the concrete transformation done by the algorithm.

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2
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2answers
182 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 ...
3
votes
2answers
399 views

How to measure ECC key size?

I have implemented a ECC key generation scheme successfully. Now I need to find ECC key sizes of each generating key pairs. I assumed that ECC key size is the size of the ECC private Key. So I would ...
1
vote
1answer
68 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 ...
6
votes
1answer
5k views

Can I remove newlines in a public key?

Can I remove new lines from the RSA public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or ...
0
votes
1answer
73 views

Key Hierarchy and key Encryption

If i have two 56-bit DES keys, and I use these two key to encrypt a 256-bit AES key. Like this $K_{AT}$ encrypts $K_{BT}$ and $K_{BT}$ encrypts $K$ What is the effective security of key $K$? Is it $...
1
vote
1answer
228 views

Intuition for random variables in cryptography

I have a simple question about the use of random variables for encryption schemes, to make sure my intuition is correct. We say $P(K = k)$ to represent the probability that a particular key $k$ is ...
3
votes
2answers
145 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(\...
1
vote
1answer
46 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 ...
4
votes
2answers
74 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 ...
4
votes
1answer
393 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 ...
1
vote
0answers
194 views

Perfect Forward Secrecy in MTI/A0

Would the property of perfect forward secrecy still be achieved in MTI/A0 for a session key that was established between C and D when one LL-key aD is revealed so that both LL-keys aC and aD are ...
1
vote
1answer
41 views

Crypto lib that use files instead of passphrase [closed]

I would like to program an application to allow people to encrypt files without using a password or pass-phrase but an arbitrary long file. I'm searching for a library that allows me to safely create ...
0
votes
1answer
64 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: ...
1
vote
0answers
50 views

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

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 ...
2
votes
1answer
68 views

Application level encryption and key renewal

I had posted this question on stackoverflow and been asked to move it to crypto. What is your view on this? What is the doability? I have a question related to encrypting data in the database, at the ...
1
vote
0answers
25 views

Deriving Minimum Description Length of Substitution Key

Given a plaintext: Now is the time for all good men to come to the aid of their country because the quick brown fox jumped over the lazy dog. and a substitution ciphertext: Mpe od yjr yo,r ...
1
vote
0answers
39 views

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 ...
2
votes
2answers
1k views

Am I understanding AES key padding correctly?

I’ld like to ensure I understand AES key padding correctly… Is the initial AES key (expanded to the key schedule) byte padded if less than e.g. 16 bytes? Is there a safe way of determining if ...
4
votes
2answers
85 views

Does a key derivation function always generate an even distribution of bits in the resulting key?

I am a student of crypto. During our study course, we went into the AES-128 algorithm. All the examples given used an initial key k, 128 bits and we only briefly touched on the key derivation of ...
3
votes
1answer
78 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 ...
5
votes
1answer
483 views

For a given plaintext-ciphertext pair, how many valid AES keys are there?

For $PT\in \mathbb{M}$ and $CT\in \mathbb{C}$, let $\mathbb{F}=\{f|f:\mathbb{M}\rightarrow\mathbb{C}\}$ be the collection of all functions from $\mathbb{M}$ to $\mathbb{C}$. Then AES encryption under ...
3
votes
1answer
54 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 ...
1
vote
1answer
259 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 ...
4
votes
1answer
47 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?
9
votes
2answers
81 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.
1
vote
0answers
33 views

cumulative secrets

Imagine a server with an authentication scheme that utilizes an element of randomness in new sessions (i.e. one that uses the secure remote password protocol). At the end of a successful ...
12
votes
6answers
1k views

Why does PBKDF2 xor the iterations of the hash function together?

The definition of PBKDF2 states that I obtain a derived key (1) by calling a pseudorandom function a bunch of times recursively: $U_1 = PRF(password, salt)$ $U_2 = PRF(password, U_1)$ … $U_n ...
1
vote
1answer
27 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?
3
votes
1answer
45 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....
4
votes
2answers
75 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 ...
3
votes
2answers
80 views

Does a key need to be signed if it is being used to decrypt a message that is already signed?

I am trying to better understand authentication. Lets say I have posted my 128-bit AES symmetric key on some forum, encrypted asymmetrically to my friend using 256-bit ECC (25519). The forum isn't ...
0
votes
0answers
28 views

Garbled table for 3 inputs

I have a truth table of a full adder with 3 inputs (A,B,Cin) and 2 outputs (S, Cout). How can I create a garbled truth table? I mean, in the general form it is ...
1
vote
1answer
196 views

Choosing primes in the Paillier cryptosystem

In the first step of key generation phase in Paillier cryptosystem given here. It's given that $$\operatorname{length}(p) = \operatorname{length}(q) ) \implies \operatorname{gcd}(pq,(p-1)(q-1))=1$$ ...
0
votes
1answer
541 views

Are there attacks on AES with 16-bit keys? [closed]

Are there known attacks on AES that uses a 16-bit key? Assuming the data can be 95MB size, and that I can request the same data over and over. For example, can someone explain to me how this code ...
3
votes
2answers
93 views

Can CMAC be used as a 128bit Key Derivation Function?

I want to derive a key a number of times for a deterministic scenario, where I can get n keys from a single one. The logic looks something like this: ...
6
votes
3answers
12k views

The modulus of RSA public key

I am studying the RSA cryptosystem. The public key consists of $(n, e)$, the modulus (product of two large primes), and the encryption exponent. I want to separate the modulus $n$ and exponent $e$. A ...
1
vote
2answers
4k views

If I have the unencrypted text and the encrypted text, can I calculate the key?

If I have the unencrypted text and the encrypted text, can I calculate the key? It seems logical based on my limited knowledge of encryption that I should be able to... but it also seems like too ...
1
vote
1answer
82 views

How would an attacker perform an exhaustive key search on a block cipher using ECB mode?

Do you always assume from Kerchoff's principle, that the attacker has access to everything but the decryption key? That is, am I to assume that to perform an exhaustive key search, the attacker has a ...
1
vote
1answer
64 views

Why are there $q^2$ keys for each equivalence class in Pedersen-van Heyst Signature Scheme?

How do you know there are $q^2$ keys for each equivalence class in the Pedersen-van Heyst Signature Scheme? My textbook says this is "easy to see", however, I am not seeing it. Is it because in the ...
4
votes
3answers
146 views

Why are there $2^{56}$ possible DES keys when there are 64 key bits?

On forums I read DES has $2^{56}$ possible keys so it takes x times to brute force it with hardware x. But there are 64 total bits of which are 8 parity bits. But those parity bits are a ...
1
vote
1answer
151 views

AES key and block size

I am trying to understand $AES$ and I wondered what happens in the case of a $128$ bit block size and a $256$ bit key. All documents I read about $AES$ told me the key expansions algorithm for $128$ ...
2
votes
1answer
254 views

LUKS multiple key slots - what's the intuition?

LUKS volumes have the ability to allow multiple independently usable passwords, as explained here: [https://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions] The intuition behind basic ...
2
votes
1answer
78 views

Can the key-complement property of DES be used against 3DES?

The comments in this recent question about the security of 3DES made me wonder if the key complement property of DES (which reduces its security by ~1 bit) can be used in the meet-in-the-middle attack ...
2
votes
0answers
35 views

Hiding the identity of a party within the Kerberos authentication scheme

In the Kerberos authentication protocol, as described here: would it be safer to replace step (1) with: $$ A \rightarrow T : A, E_{K_A{_{T}}}(B, N_A) $$ so that a passive adversary does not know ...
0
votes
1answer
39 views

Synchronous Stream Cipher Problem

Hello I am facing a problem trying to solve this question in the picture. Does anyone know how to produce the mentioned 32-bits of the key stream? The plaintext in this case is ...
3
votes
1answer
57 views

Updating the seed key of a PRNG while maintaining initial entropy?

Consider a seed key ($n$-bit long) is completely random and entropy of random variable is $n$ and PRNG is using deterministic algorithm and that that deterministic algorithm does not add any entropy ...
0
votes
0answers
28 views

key hierarchy management and master key

I have this equation, $E_{K_{as}}(E_{K_{bs}}(K_{ab}))$ which means $K_{ab}$ is encrypted by $K_{bs}$ then whole packet is encrypted by $K_{as}$. I think the key structure is $K_{as}$ is the master ...
0
votes
0answers
34 views

Can we use more than one irreducible polynomial in AES?

I understand that the irr. poly is used to form the s-box (and inv. s-box), the key schedule and the mix columns. But could we use a different irr. poly for the mix columns and another for the key ...
3
votes
1answer
176 views

Provable security of cryptographic hash functions

I am working on the following exercise question: Consider the following construction of a “keyed” hash function from Katz & Lindell (ex. 7.22 (1st ed.)/ 8.21(2nd ed.)). Gen : On input $1^...
0
votes
1answer
81 views

Storing RSA private key

Currently I'm developing an application where users generate their own pair RSA keys in order to achieve a secure communication with my server. Also clients are able to communicate directly, sending ...