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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1answer
47 views

Counter Mode: how to choose the nonce part of the counter? [duplicate]

Suppose: The "counter field" is about: NONCE || CTR-VALUE. I have multiples messages $M_a, M_b, M_c, \dots$ Each message can be divided into x-bits blocks ($M_{a1}, M_{a2}, M_{a3}, \dots$). Each ...
3
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1answer
220 views

Can all asymmetric key pairs be reversed?

After reading about public/private key cryptography, there are still a few points I don't really understand. Based on the way (I understand) challenges work, the public key is used to encrypt a ...
7
votes
2answers
343 views

Is it secure to derive an AES key from a MAC?

I'm working on a project where we need to encrypt a large number of files and store them on the cloud. And I'm wondering if the following process would be secure (we have a “Hardware Security Module” ...
1
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1answer
63 views

Private Key - Memory Lifecycle

I often heard about private key storage, but rarely about key life cycle in memory. For example, when SSL is used from one peer, the private key is used to sign messages or decrypt other peers' ...
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1answer
65 views

Is encryption mainly using Diffie-Hellman Key Exchange?

I know how Diffie-Hellman Key Exchange works. Is this the main way of encrypting with PGP, ssh, ssl (https), DKIM, ...? I wonder if Diffie-Hellman is the clue to understand how encryption with ...
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0answers
57 views

Security implication of exporting private key [migrated]

I have a key pair stored in GPG Keyring. If I export it to an ASCII Armored format, am I removing any layers of security as long as the exported key stays on the same server as the key ring itself? My ...
3
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2answers
90 views

Combining two keys

What is the most secure way to combine two "random" keys X of size k (k ≤ 512 bits) and Y of size 512 bits in one key Z of size k? Result Z will be used for encryption/decryption with various ...
3
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1answer
54 views

Session-specific Symmetric Key Derivation Using SHA256

I was wondering if there were any security implications of deriving session keys from a symmetric key using SHA256 in the following manner: $Ks = SHA256(Nonce||K)$, where $Nonce$ is the session ...
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2answers
174 views

How exactly does key whitening manage to increase security?

Wikipedia states that key whitening increases security: In cryptography, key whitening is a technique intended to increase the security of an iterated block cipher. It consists of steps that ...
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2answers
121 views

Public key Issue - same key pair as existing one? [duplicate]

My question is a bit naive, but what if someone generates the same RSA key pair as someone else? This person would have the same private key and so would be able to decrypt messages not intended to ...
1
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1answer
53 views

Choosing primes in the Paillier cryptosystem

In the first step of key generation phase in Paillier cryptosystem given here. It's given that ( length($p$) == length($q$) )$\implies$ gcd$(pq,(p-1(q-1)))$=1 where length($k$) = # bits in ...
2
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2answers
122 views

What exactly does a key do?

I am getting to grips with cryptography as a total newbie, and am struggling with encryption "keys" and how to visualize them. From http://computer.howstuffworks.com/encryption.htm/printable: ...
2
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2answers
127 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 ...
3
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1answer
194 views

RSA example-calculation: Public Key = Private Key (e = d)

I am a bit confused. I just calculated manually the single steps of RSA for an implementation with small numbers and suddenly $d$ was equal $e$. Please help me understand what I am doing wrong. ...
2
votes
2answers
172 views

Password-based encrypted key storage?

RFC 5959 specifies the encrypted storage of private keys based on PBKDF2-HMAC-SHA-256 and AES encryption (in ECB mode). Is there a particular reason AES is used, instead of simply XORing the key ...
2
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1answer
61 views

User-specified PBKDF2 password, salt, and iterations limits

For a decentralized login where a user is left to select the password, salt, and iterations, what minimums for each should be enforced? In other words, because none are ever stored by the ...
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1answer
54 views

How can the key size be calculated [closed]

If the decrypting key is 448, then what is the key size? Suppose I am encrypting a plain text with a key by choosing some random numbers between ...
2
votes
2answers
471 views

Does the secret key used in AES have to prime?

I’ve looked around this site and the web quite a bit, but can’t find a definitive answer on whether or not the secret key $k$ used in the AES crypto-system has to be a prime number? Or can you just ...
2
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1answer
66 views

Number of keys when using symmetric and asymmetric encryption?

Quoting part of my homework/assignment: How many keys are required for secure communication among 1000 person if: Symmetric key encryption algorithm is used? Asymmetric key encryption ...
4
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1answer
158 views

Understanding hash entropy

I have been told that one advantage of using a hash function is that it spreads entropy over all input bits. But it also seems to be true that a bad hash algorithm can make things less random. But how ...
1
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1answer
60 views

x509 CA trust question

I'm trying to understand the logic of CAs, trust and client certificates. I have a general understanding but am having a tough time bridging some gaps. In a hypothetical situation a software system ...
2
votes
2answers
178 views

DES with actual 7 byte key

Do we have any library or any mechanism where we can use true 7 byte key for DES instead of 8 byte key. I need it for keys analysis in DES and 8 byte key requirement for associated library is creating ...
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1answer
48 views

Do I need two keys for AES CBC and HMAC or can I use the same key for both operations?

I am setting up a Python program to encipher messages on the following basis: -from my password, generate 32-byte key from SHA256(password) -generate a 16-byte IV from a PRNG -measure the length of ...
0
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1answer
53 views

Spurious keys filter [closed]

Is there any possible way to filter a key space in a crypto-system to get a set of keys that decrypts out a valid text (text that is in same language or readable)? I tried a random approach and got ...
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votes
1answer
51 views

Positioning of keys in encrypted text

I'm just looking at very simple encryption. I've noticed that the key is typically either at the front or at the back of the encrypted text. This is quite easy to break if you know the key. It can ...
2
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2answers
182 views

Does AES-128 have the same strength as AES-256 with a padded key?

When I use the same 128-bit key for AES-128 and AES-256 with a known/public padding for the latter, is there some weakness in AES-256 that is not present in AES-128 with essentially the same key? ...
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0answers
62 views

Hill cipher key space

Key space is the set of all possible keys that can be used to generate a key. We using the number of valid key to describe it. I've given a hill cipher of block size $k$ over alphabet of size $p$, ...
5
votes
1answer
230 views

Secure AES Key Generation via Salsa20?

I am not creating my own cryptography or anything, but to learn about the Dos and Donts of cryptography, I am looking into AES encryption and ways to generate keys for that. As far as I've ...
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3answers
241 views

What is h in the improved solution of RSA algorithm?

I am trying to implement a proposed improved algorithm of RSA . Here the author has increased the number of exponents. However I am unable to understand what $h$ is in the Key generation step. Can ...
0
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1answer
261 views

Decrypt AES-128 with key file but missing IV? [duplicate]

I want to decrypt a file that has been encrypted using AES-128 in CBC mode using OpenSSL. I got the “.key” file – which is 32 digits – but when I try to decrypt with OpenSSL, the program asks me for ...
5
votes
1answer
198 views

Is it possible to weaken a bitcoin private key by “using” it elsewhere?

What are the increased possibilities (if any) of being able to crack a private key given the following: The associated bitcoin (ECDSA Secp256k1-based) public key is known. The private key has been ...
0
votes
0answers
32 views

Is it possible to weaken a bitcoin private key by 'using' it elsewhere? [duplicate]

What are the increased possibilities (if any) of being able to crack a private key given the following: The associated bitcoin (ECDSA Secp256k1-based) public key is known. The private key has been ...
2
votes
1answer
270 views

Is it true that for RSA with no padding, the length of data must be equal to the length of key?

The question pertains not in terms of security but computing operational functionality, as it how the computation is done. Is it true that for RSA with no padding, the length of data must be equal to ...
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1answer
72 views

How does the key size per data bit influence the security?

The likelihood of breaking, for instance, an AES-128 cipher is 100% after $2^{128}$ tries in brute force, meaning that I've got to try $2^{128}$ keys to certainly break it. What if I (hypothetically) ...
2
votes
1answer
142 views

Do any one-key-of-many cryptographic schemes exist?

I'm pretty sure I understand how public/private key cryptography works. Anybody can encrypt a message using a well-known public key, but only the person who holds the private key can decrypt it. My ...
1
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1answer
148 views

What is the best way to share a shared secret key over HTTPS to be used for HMAC authentication?

I am writing an application in Java that will be using SHA-1 HMAC message authentication. From what I understand, a connection over HTTPS is considered secure enough to share a secret key in plain ...
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0answers
42 views

Random numbers for Master Key and Key_block

Exploration through RFCs concludes that random numbers used in the creation of Master Key and Key Block(Key material for Encryption Key and Mac Secret) are from ServerHello.random and ...
0
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1answer
96 views

Prime factors of non-random keys

I have been working on a challenge i found on the internet. It is as follows: You've stumbled onto a significant vulnerability in a commonly used cryptographic library. It turns out that the ...
2
votes
1answer
215 views

Find out which keying option is being used in Triple DES?

As far as I know, there are three standard options for the three keys $K_1$, $K_2$ and $K_3$ used by 3DES: Three distinct keys. The first and last key are equal: $K_1$ = $K_3$. Three equal keys: ...
2
votes
1answer
93 views

Secrete message sharing using N private keys

I'm looking for an encryption scheme that could possibly meet the following requirements. Let, $X = plaintext$ $M = (pub, priv)$, where $priv == (Ky + Kz)$ Given ...
3
votes
1answer
103 views

Does re-iterate AES128 with different keys gives any benefict?

I'm not cryptography expert (well, I'm here after all!) but I have this doubt… Suppose I have 2 different keys: secretkey1 secretkey2 And a plain text: myReallySecretPlainText If I use AES128 ...
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2answers
124 views

Cryptanalysis of an certain algorithm

Is an attacker of an cryptographic algorithm allowed to change order of sub-keys but not changing their number in attack? Would it be called an attack on broken algorithm of cipher?
3
votes
2answers
253 views

If PGP and GPG both follow the OpenPGP standard, are they 100% compatible in all use cases?

If someone gives me their PGP key, can I use it with GPG, and vice versa, all the time (100% interchangeable)? Or are there times when they are not compatible, when only PGP can be used with a PGP ...
3
votes
1answer
103 views

How to protect against ephemeral key reuse in some signature schemes?

Given that some signature schemes (for instance Elgamal) use an ephemeral key that cannot be reused ever. How do people usually protect against this? I'll elaborate more: if you reuse the ephemeral ...
2
votes
2answers
379 views

Can curve25519 keys be used with ed25519 keys?

Can curve25519 keys be used with ed25519? I'd prefer to use ed25519, but there isn't a fast java version. For my application, I'd like to use curve25519 until I can get a faster ed25519 for java. ...
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4answers
318 views

Messages exchanged between Bob Alice are encrypted safe?

Can you help me understand the following reasoning? If Alice sends Bob a message and that message is encrypted with two keys simultaneously: a symmetric key (Ks) and Bob's public key. The symmetric ...
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1answer
130 views

Generate keys with k3d3 / ed25519-java

I'm trying to use a java implementation of ed25519. In the code, I can't find any functions that generate keys. My experience with cryptography is limited to about three weeks of asking questions on ...
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1answer
66 views

Why is the security of block cipher not a function of key and tweak?

The proofs and security of block ciphers constructed especially of Luby Rackoff Constructions and Feistel Networks is based on the number of queries and round functions. The security measure is always ...
1
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1answer
567 views

Is Curve25519-java secure?

I have only about 2 weeks of cryptography experience mostly in the form of questions on bitcoin.se. Is Curve25519-java up to date with current Curve25519 standards? Is Curve25519 itself secure? ...
2
votes
1answer
93 views

Proof of shared secret through key derivation

Alice gives a random key $K$ (e.g. 32 bytes long) to Bob through a secure channel. Bob want to prove to Alice through an unsecured channel that he knows the key. Is it secure for Bob to send ...