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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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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0answers
28 views

How can I identify this (I think) symmetric encryption? [closed]

I'm working on a CTF and I'm trying to decrypt some cipher text. I've got a key and the cipher text, but I'm not sure how to determine the algorithm used. ...
0
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1answer
44 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 ...
3
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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(\...
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2answers
73 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
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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 ...
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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: ...
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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 ...
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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 ...
3
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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 ...
3
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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 ...
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1answer
258 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
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?
3
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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....
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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?
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2answers
175 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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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.
4
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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 ...
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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 ...
3
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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 ...
2
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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 ...
3
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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: ...
0
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1answer
539 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 ...
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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 ...
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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 ...
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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 ...
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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 $...
3
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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 ...
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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 ...
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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 ...
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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 ...
0
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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 ...
1
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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 ...
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1answer
28 views

Symmetric : Generate new key from old ones

Symmetric keys should be refreshed regularly. Is is terribly wrong to first agree on $N$ independent keys and then generate the key $k_j$ with $j>N$ by computing some form of hash on the keys $k_{...
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2answers
114 views

Shannon theorem of perfect secrecy

From the class: Shannon Theorem: For a perfect encryption scheme, the number of keys is at least the size of the message space (number of messages that have a non-zero probability). Proof: ...
1
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1answer
233 views

HMAC Secure Key Exchange?

Within RFC 2104 section 3 there is discussion around keys (below). How are these keys agreed upon/distributed? Practically speaking is asymmetric crypto a requirement to "bootstrap" and distribute ...
4
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1answer
360 views

What is considered a “weak key” in AES?

I need to construct an AES key from an array of bytes (in Java), but I first I have to check if the key created from these bytes would be weak. Java can check for weakness for DES, but not for AES. ...
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0answers
64 views

Decrypting a file encrypted with AESCRYPT using key instead of password

i have encrypted a file using aescrypt and took memory image while the file was being encrypted and hence have the key that was used for encryption in the image but not the password, can i decrypt the ...
6
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3answers
930 views

AES key reuse and guessing the key

Bit of a noob question and a fair bit of Googling didn't help. I understand that the current encryption standard is AES256. A few questions Is the point of this (and other encryption techniques) to ...
4
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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 ...
4
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1answer
98 views

How does a company like Apple keep its keys safe? [closed]

Whatever key is used to sign new iOS updates (for example) must be incredibly well-protected. How does a huge corporation like Apple keep those 4096 bits safe?! Same goes for SSL keys for websites ...
3
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2answers
27 views

X509 converted to Encrypted and Signing keys

We have proprietary tool which takes a p12 file and generates a .key file. Inside the key file, I see two PEM formatted sections: Encrypting Certificate and Signing Certificate. When I open them on my ...
3
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0answers
73 views

How common are weak RSA keys?

There exist certain attacks that can be used against RSA keys whose prime factors are of specific forms, such as one by Coppersmith. How common are these RSA keys? If you generate primes randomly, ...
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1answer
60 views

Number of shifts in DES key schedule

In DES key schedule some rounds use one left shift while others use two left shifts. What is the reason behind this?
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76 views

Confidentiality then Integrity with different keys

Can anyone describe how we can do what is said in the below sentence which is in Mark Stamp crypto slides (PPTX) on slide number 101 : Can do a little better - about 1.5 “encryptions” The whole ...
2
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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 ...
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1answer
61 views

Why does a hacker need to crack the key to an encrypted file, instead of just brute forcing the password? [closed]

Most encryption softwares don't seem to have a trial limit. So why would a hacker need to crack the key, or even need to know the salt value, if he can just brute force the 6-8 digit password?
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3answers
114 views

Choosing which is public vs private key

When I calculate two RSA keys, what if anything, would make any difference which I call the public vs which I call the private key?
3
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1answer
108 views

Question on 3DES keys

The official NIST publication I saw says for federal applications 3DES with three keys should be used. I have such questions: what does it mean federal? Does it mean for industrial applications that ...
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1answer
80 views

Compression in key generation of DES algorithm

Does anyone have a pseudo-code or an algorithm or even a diagram of the compression (pc2) of the DES algorithm? I can't find a relation between the bits that are dropped, even when I do it manually ...