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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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How does Twofish avoid weak keys if it uses key-dependent S-boxes?

From section 7.2.2 of the Twofish paper, the four S-boxes for the 128-bit cipher are generated with: $$\begin{align} s_0(x) &= q_1[q_0[q_0[x] \oplus s_{0,0}] \oplus s_{1,0}]\\ s_1(x) &= q_0[...
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66 views

Cryptography concept concerning keys and key-space [on hold]

What cryptography concept is someone referring to if he says that our galaxy is like key-space and the rest of our universe is like universe of possible numbers where that key-space exists. If you ...
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19 views

Extract the slave key and encryption key [closed]

I am trying to solve this problem and I need help if possible Suppose a Hardware Security Module (HSM) has a master key KM (56-bit) in its secure memory. It also has a slave key KS (56-bit) ...
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1answer
37 views

Key, plaintext block and ciphertext block permutations question

Question: If a cipher’s key size is $k$ bits and its block size is $b$ bits, how many possible keys are there, how many possible plaintext blocks are there, and how many possible ciphertext blocks are ...
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22 views

Implememtning GKE+P Group Key agreement protocol on nodejs [migrated]

I try to implement the GKE+P protocol presented on paper Flexible Group Key Exchange with On-Demand Computation of Subgroup Keys by Michel Abdalla, Céline Chevalier, Mark Manulis and David Pointcheval ...
10
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4answers
3k views

If Kerckhoff's Principle holds, why do we need a cipher at all?

I understand Kerckhoff's principle, in a very practical sense, that the best attack that can be performed on a given cryptographic algorithm should be only as practical, if not less practical, than an ...
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0answers
28 views

What is connection between curve used for ec_keypair generation and ClientHello extension?

Im currently experimenting setting up my first SSL server and don't understand the following scenario: My server has a generated ECC keypair with group identifier $A$ (e.g Brainpool256r1). During TLS ...
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0answers
11 views

Production Ready Message Format Standart for Key agreements on top of XMPP

Greedings, I try to run group key agreements on top of XMPP thus I want somehow a production used message format for key agreement. As far I found theese: XEP-0384: OMEMO Encryption XEP-0102 But all ...
2
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2answers
19 views

Mutual keys protection/wrapping

Is there a known risk in having two keys wrapping each other? Let's say, an adversary has access to both AESkey1(key2) and AESkey2(key1). Does it make it much easier for him to recover the keys?
16
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1answer
4k views

Related-key attacks on AES

According to Wikipedia: Related-key attacks can break AES-192 and AES-256 with complexities $2^{176}$ and $2^{99.5}$, respectively. What are the requirements for these attacks (i.e how many ...
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0answers
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PCI DSS requirement 3.5.3

3.5.3 Store secret and private keys used to encrypt/decrypt cardholder data in one (or more) of the following forms at all times: ............ As at least two full-length key components or key shares, ...
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34 views

Why would one split HKDF output into multiple parts instead of expanding it multiple times

Reading the implementation details of Signal's approach on double ratchet algorithm I noticed the following key derivation procedure for using AES-CBC with HMAC: HKDF is used (...) to generate 80 ...
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0answers
13 views

GlobalSign cert in Trusted root for Google Services shows Sha1. Security postures

"GlobalSign" certificate in Trusted Root Certification Authorities for Google Services shows Sha1. Security postures are different than just 2-3 yr ago. At my home, router bought 2016, networked; ...
0
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1answer
40 views

ED25519 Child Key Derivation

Let's say I generate a keypair for a user with go's ed25519 package: pub, private := ed25519.GenerateKey(nil) And I want to generate additional child keys as ...
3
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2answers
373 views

How much extra security does key wrapping provide?

Wikipedia says: Key Wrap. Key Wrap constructions are a class of symmetric encryption algorithms designed to encapsulate (encrypt) cryptographic key material. The Key Wrap algorithms are intended ...
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2answers
579 views

Why can we always assume that $Gen$ algorithm choose key uniformly?

Disclaimer: This is exercise 2.1 in Katz-Lindell book. Given a (symmetric) encryption scheme $\Pi=(Gen,Enc,Dec)$ where $Gen$ takes the security parameter $1^n$ as input and generates a key $k$ of ...
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1answer
33 views

Attack vector difference when not allowing repetitions in BIP-39

We are using a 12-word scheme BIP-39 mnenemonic key generating scheme that creates an entropy of 128-bit that is then used to generate a seed that in turn derives a private key for the user. It ...
0
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1answer
134 views

Key Entropy meaning Help

Can anyone help me understand key entropy the mathematics behind it and the uses for it? I understand most of it but I just want to understand what does $\log 2$ do like if I do. $\log 128 / \log 2 = ...
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0answers
76 views

Implications of identical round keys in Rijndael

When reading up on the Rijndael key schedule, I learned that the master key itself is used as a round key directly before the key schedule generates additional round keys. When a 256-bit key is used, ...
2
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1answer
101 views

Does the public key and private key for WhatsApp only remain within a WhatsApp account

The world of cryptography is starting to really intrigue me admittedly. I initially hated it because it looked too hard Mathematically but now it looks cool :) Got a good question for the experts and ...
7
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1answer
129 views

How to find fixed points for DES weak keys

Can someone explain me this please I am a bit confused? It's from a texbook I am reading (block cipher companion) it says that: each weak key has $2^{32}$ fixed points $m$ where $\operatorname{...
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1answer
52 views

Does repeated xoring of the (same) key K lower the entropy of K?

If a symmetric encryption key $K$ has been generated by some recommended (NIST for example) RBG then we should have a key with high entropy. But if we xor other bit-strings (e.g. IVs, other keys, etc....
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5answers
3k views

Is a PRG more costly than AES or any other encryption standard?

I know that there are many encryption standards that take a key and sometimes an IV, and produces a cipher-text (the most prominent one is AES). These standards usually involve many rounds of addition ...
2
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1answer
34 views

mDP kay agreement protocol where z's are found on the step where the common key is generated?

Whilst I was studying the mDP protocol I came across into the following step: Group Key agreement: Each $U_i$ checks whether $z_1 \bigoplus ... \bigoplus z_n = 0$ and whether all signatures $\...
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0answers
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Asymmetrical encryption with multiple sufficient key-pairs [duplicate]

I have the following requirement: There are N public/private RSA key pairs. The encrypted data must be decryptable by any of the private keys alone, but not by any other key. For encryption, the ...
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Asyncronous Rachet tree: How user movability is handled is the Rachet tree being recreated?

As I have read the latest state of art in group key agreement is the Asyncronous Rachet Tree. But in applications like IRC that exists high user movability (users join in ans leave the room). Is ...
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1answer
79 views

Find $F(2x)$ from $F(x) = a^x \bmod p$

Given $F(x) = a^x \bmod p$, where $a$ is a primitive root of $p$, Is it possible to work out what $F(2x)$ or $F(3x)$, etc if you know what $F(x)$ is but not $x$. If you use $F(x)$ then $F(2x)$, etc ...
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1answer
46 views

Signal/TextSecure multiparty Chat. Does the protocol transmits a symmetric key?

As I look over the TexSecures specifications for multi-party chat I have noticed this. Also as far as I understood in TextSecure (now known as Signal) the minimal steps required to do a secure ...
3
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1answer
106 views

Keys-space for a restricted substitution cipher

How can one calculate the key-space for a restricted substitution cipher? A restricted substitution cipher is one where no letter is assigned to itself. For an alphabet with 26 letters how many keys ...
0
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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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0answers
69 views

Signal Sender Keys: Why it works and which is the common key at the end?

As I has read upon "WhatsUp Encryption Overview" when a client receives a sender message then it performs the following actions: Decomposes Sender Message to ...
7
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1answer
127 views

HMAC-SHA-512 with a 256-bit key

I am implementing hmac-sha-512 in an integrated system. However, one subsystem is only supports the use of 256-bit keys. I read in https://tools.ietf.org/html/rfc4868 that: However, note that [...
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2answers
40 views

Maximum number of possible keys for a fixed-length password?

I'm reviewing some information and possibilities regarding key space size following a unique password requirement, as it were. This particular requirement is a fixed-length password of 12 characters, ...
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1answer
60 views

How do i manage encryption keys with a cloud provider?

I would like to provision services from a Software as a Service (SaaS) provider. This is multitenant environment (multiple companies will be using a single instance of the application, with a single ...
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2answers
91 views

Two working decipher keys giving various, valid results for one ciphered message - is it possible?

Let's assume following scenario: There's a ciphered message. Two decipher keys (let's name them A and B) are known. Message deciphered with key A gives valid result - normal text but with no secret ...
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0answers
28 views

GPG Sub Key Renewal Questions

Last year, I followed this guide to create two GnuPG Smart Cards; one card with the Primary Key and the other card with the Sub-keys. I noticed that the sub keys were close to expiring so I renewed ...
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1answer
76 views

What happens at this part in the key schedule of a Speck…?

I am trying to figure out the process behind the Speck block cipher. I understand how XOR works (Exclusive-or) when you take 2 strings of bits and you want to XOR them together. However, in the key ...
3
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1answer
70 views

Basic Vigenere Cipher

I'm taking my first cryptography course and having trouble deciphering some Vigenere encrypted text. I was able to crack the first one: I'm having difficulty with the other two. I think the ...
2
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1answer
124 views

Getting a Keeloq manufacturer key

I have seen a lot of articles and research papers about breaking the Keeloq algorithm. My understanding is that the hardest part is getting the 64 bit manufacturer key. Some methods use crypto-...
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0answers
67 views

Need help decyphering message [closed]

THEIR DIFFERENCE WILL REMAIN, LONG AFTER THEY ARE DEAD Dear Friend, IV IV 12 8 14 - 19 14 18 9 13 IV I C C 9 17 IV 17 12 IV 8 14 IV 7 F 14 IV 7 19 D IV 12 15 F 19 E IV 8 17 IV 7 12 15 F 19 13 17 9 E ...
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Nature of risk(s) from KeeChallenge XML file stored in cloud at Onedrive

As a noob user of KeePass2 on Windows desktop and Keypass2Android on my phone, supplemented by YubiKey Neo configured for hmac-sha1 challenge response, I noticed that Keepass2Android appears to store ...
3
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1answer
50 views

Does it make sense to have long SSH Key with shorter Passphrase?

If we encrypt our data with a longer SSH key which is protected by a shorter passphrase (with a decent entropy), then the limiting factor is entropy of the passphrase. So why do we use a longer key at ...
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0answers
36 views

Is there hierarchical key generation that completely tolerates leakage?

Is there a hierarchical key construction algorithm that achieves forward/backward privacy with any (unlimited) leakage of private non-master keys? What I mean is that if there's an unbounded number ...
2
votes
1answer
70 views

Ciphertext to different plaintext

Is there any algorithm for generating the same ciphertext from different plaintexts, depending on the key used? This seems similar to Honey Encryption, but I don't need to have every key give ...
5
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3answers
3k views

Key management for military GPS receivers

I wonder what encryption scheme is used in high-precision encrypted GPS streams (the so-called “P(Y) code”). If there's a master key needed, then it has to be in every device. Yet the master key doesn'...
2
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2answers
77 views

Trustless exchange without a third party

Is there a cryptographic (or even not entirely cryptographic) way of exchanging objects between Alice and Bob that would not require a third party, and Alice and Bob would not need to trust each other?...
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0answers
51 views

Is it possible to successfully encrypt/decrypt in DUKPT using different sized BDKs?

We are having our P2PE Solution validated against the PCI P2PE standard. We currently use a TDEA 2-key based BDK, and IPEK in both the encryption and decryption environments. ANSI X9.24-1 (2009) ...
5
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1answer
397 views

If the plaintext contains the key used to encrypt the ciphertext, is the ciphertext easier to decrypt?

I have a symmetric key which can be used to encrypt plaintext and decrypt the resulting ciphertext. I use it to encrypt a plaintext which is a copy of the aforementioned key. My adversary gets a copy ...
2
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1answer
57 views

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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2answers
115 views

Does AES use different keys for each block of plaintext?

If you have 4 16-byte blocks of plaintext to encrypt does each block have a different 128 bit original key? Or do they all use the same?