2
votes
2answers
138 views

Security of CFB on a public channel

Given a server that broadcasts all received data to all connected peers (except the sender), two participants can have an encrypted conversation using a self-synchronizing method like CFB and some ...
2
votes
3answers
505 views

How can I accomplish Key Derivation in JavaScript?

I need to take a potentially weak user password and derive a strong key for AES encryption in JavaScript. How can I do this? I expect the hardest problem is generating a good random salt - perhaps an ...
2
votes
1answer
341 views

How was 256-bit WEP cracked as well?

WEP is now considered as insecure. But how about the 256-bit WEP? Could someone explain why a 256-bit encryption isn't enough? 'A 256-bit WEP system is available from some vendors. As with the other ...
2
votes
1answer
228 views

Selecting bijective functions for permutations

How would one go about selecting an appropriate bijective function for introducing permutations into a cipher or hash? For example, $f(x) = x+1 \space mod \space n$ is a bijective function, but isn't ...
2
votes
1answer
203 views

Securely generating passwords based on a secret and a public identifier

I'm trying to create a good scheme for generating passwords in my systems management scripts. What I'd like to do is have a secret key (let's say hello123), which I ...
2
votes
1answer
775 views

Is a PBKDF2-derived master key easier cracked if very many Data Protection Keys are derived from it?

I'm referring the NIST document about PBKDF2, NIST Special Publication 800-132, Recommendation for Password-Based Key Derivation, Part 1: Storage Applications, Page 8 and 9, section 5.4 Using the ...
2
votes
1answer
81 views

How does the possible attack on passwords and salts mentioned in PKCS#5 v2.1 work?

From PKCS#5 v2.1, 4.1 Salt (page 6, emphasis by me), also in v2.0, RFC 2898: In password-based encryption, the party encrypting a message can gain assurance that these benefits are realized ...
2
votes
2answers
415 views

Generating IV in TLS 1.2

I'm writing a TLS 1.2 implementation (in C#) using a custom protocol. My question is how to generate the IV attached to each message, I don't want to use RandonNumberGenerator because I've heard it ...
2
votes
1answer
332 views

Security of Salsa20 with some known plaintext?

Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known? Assume that a different IV and Key are generated before each file is ...
2
votes
1answer
234 views

Can prepending “junk” be equivalent to an IV when encrypting using CBC?

We are encrypting a small positive integer (1-1000) with a constant key using AES256 encryption. We are considering two approaches to make this secure; use an initial vector (which we then need to ...
2
votes
2answers
550 views

Does key authentication in SSH protect from MitM?

How do cryptography in SSH(2) work (secure channel establishment, authentication)? Does key authentication in SSH(2) protect from MitM by providing authentication and integrity and why?
2
votes
1answer
69 views

Comprehension question on a signature protocol based on the RSA assumption

We have the following two-party protocol between Alice and Bob. Alice sends messages $m_1, m_2, \ldots \in_R \mathbb{Z}_n^*$ to Bob and Bob signs these values by calculating $v_1, v_2, \ldots \in_R ...
2
votes
2answers
571 views

Using salted hash as password for easy memorization without reuse?

I had an idea earlier: Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a key between sites, and include the site's name as a salt? For example: ...
2
votes
1answer
299 views

Understanding one-way hash functions construction

I understand the needs that lead to the development of cryptography and I am quite familiar with the uses we make of the cryptographic tools. But, as a programmer, I am conditioned to see them as ...
2
votes
2answers
140 views

Key Exchange and anonymity issue

If Alice (sender) sends a private message embedded with public key of the Bob(recipient) through onion network, so in this key exchange, does Bob remains anonymous to Alice as Alice knows about the ...
2
votes
1answer
59 views

Equivalents to a physical hat+shaking?

I would like a multiparty protocol, secure in the honest-but-curious model at least, but hopefully other situations as well, that can do the following: every party among $\{P_1, P_2, \ldots P_n\}$ ...
2
votes
1answer
375 views

Can you help me understand how RC4-52 is done using pen-and-paper?

I've played a lot with VIC and enjoy its complexity and effectiveness as a field cipher. However, RC4 has caught my attention lately and I've read there is a RC4-52 variant that can be done by hand. ...
2
votes
1answer
312 views

What information to include is the 'info' input for HKDF?

The RFC states the following: 3.2. The 'info' Input to HKDF While the 'info' value is optional in the definition of HKDF, it is often of great importance in applications. Its main ...
2
votes
1answer
524 views

Nonce role on stream ciphers

Modern stream ciphers usually predicts the usage of a nonce (also termed as IV) in the cryptosystem. The cost of initializing the cipher with the nonce varies from algorithm to algorithm (for ...
2
votes
1answer
526 views

Digital signatures in SSL/TLS-like protocols

The TLS protocol includes an optional Server Key Exchange message that is signed by the server. It seems to me that this message is digitally signed only to prove to the client that the message ...
2
votes
2answers
189 views

Name for identical operations for encryption and decryption

Is there a name for the property of a cryptographic algorithm that the operations for encryption and decryption are identical, i.e. $E_k(x) = D_k(x)$ and accordingly $E_k(E_k(x)) = x$? An example ...
2
votes
1answer
122 views

Using UMAC with stream cypher

I understand that most stream ciphers, due to being applied with a simple XOR, are specially fragile against data tampering, and must be used with some MAC mechanism. So I am investigating the use of ...
2
votes
1answer
94 views

What is the most secure way to let Alice “input” her private key, transfer it to the server and decrypt the message?

What is the most secure way to let Alice "input" her private key, transfer it to the server and decrypt the message? (Then destroy the private key on the server) Every connection is using SSL. ...
2
votes
1answer
95 views

Is there a big RSA Data Set

Is there a big dataset containing RSA public $(n,e)$ and private keys $d$ and primes $p,q$ where $n = p.q$ ?
2
votes
2answers
233 views

What are the cryptographic assumptions in the Dolev Yao model?

In the Dolev Yao model for interactive protocols, the cryptographic primitive (encryption, for example) is considered as a blackbox. Does blackbox here mean that the primitive is to be considered CPA ...
2
votes
1answer
540 views

using Post-quantum asymmetric ciphers instead of RSA

We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ...
2
votes
1answer
6k views

What exactly is addition modulo $2^{32}$ in cryptography?

EDIT: I've been confusing this the whole time. What I've been wanting to say this whole time is addition modulo $2^{32}$ not addition modulo 32 as the question originally said. Thanks for pointing ...
2
votes
1answer
892 views

Shamir Secret Sharing - Threshold decryption implementation

I'm implementing Shamir secret sharing in C using OpenSSL. I've split up the private key and I'm ready to start decrypting the original message using some of the shares. I set $n = 5$ (5 shares ...
2
votes
2answers
224 views

RSA keys finding when messages are known

I have this situation, where, in a game, people send messages to each other (game moves etc...) These messages need to be encrypted, and should only be readable by the destination person. I am using ...
2
votes
1answer
402 views

server side Javascript security

It is accepted that the javascript library lacks the ability to create an adequate PRNG. My understanding that this was mainly due to the limits of a sandboxed browser enviroment that javascript ...
2
votes
1answer
924 views

How to test distribution of a hash function?

From what I've found, it is generally accepted a cryptographic hash function like SHA-2 has an evenly, randomly distributed output. Is there a way to test this without running through the entire ...
2
votes
3answers
450 views

Can we construct fully homomorphic encryption scheme based on non-circuit approach?

At present, all FHE scheme are be constructed based on circuit approach. Can we construct fully homomorphic encryption scheme based on non-circuit approach? Is Polly cracker non-circuit approach ?
2
votes
1answer
1k views

Shortcuts / practicality of brute forcing block cipher (AES) + ECB with known plaintext

I know the plaintext (26 bytes long) and cryptotext of block cipher (suspected to be AES) in ECB mode. I can generate hundreds or thousands of such samples, but the samples are not arbitrary. What are ...
2
votes
1answer
1k views

BouncyCastle Elliptic Curve implementation

I'm implementing ECDH key exchange in C# using the BouncyCastle library and I'm having a hard time understanding the elliptic curve side (FpCurve). ...
2
votes
1answer
3k views

Calculating the inverse modularity of the determinant for Hill cipher

I'm trying to decrypt a message encrypted with Hill Cipher, but I don't understand how to find the determinant so it solves the equation $det * 1/det = 1 mod 26$. The determinant for my key matrix is ...
2
votes
1answer
320 views

What are the safe ways to derive HMAC key using block cipher?

Suppose we have a state of block cipher initialized with some key unknown to us, that is, we have the state after running key schedule, but we have no access to actual key or subkeys, all we can do is ...
2
votes
1answer
925 views

Self-expiring symmetric keys, or: cryptography in absence of secure deletion

I can encrypt some data D using a random symmetric key K, obtaining a ciphertext C, and then encrypt K with my public key Pub and obtain H. So far so good: I can only decrypt C if I have H and my ...
2
votes
1answer
393 views

Why can't Homomorphic encryption schemes support algorithms with conditions/branching?

If it isn't already apparent from the title of my question, i should make clear that I have only a very basic understanding of homomorphic encryption. I would like to know why homomorphic encryption ...
2
votes
1answer
219 views

How is the EAX-mode used in EAP-PSK (RFC 4764)?

According to the specification of RFC 4764, contents in EAP's third message and fourth message are required to be encrypted by AES-128 in EAX mode (also called protected channel). In RFC 4764, the ...
2
votes
2answers
260 views

Stream cipher malleability

Considering a stream cipher that produces a ciphertext $c$ from a message $m$ and a key $k$ is it possible to apply operations (multiplication and/or addition) directly to $c$ without knowing the key ...
2
votes
1answer
191 views

How many different keystreams can I produce with AES in Counter Mode?

I'm using a 64-bit nonce (incremented between the streams) and a 64-bit counter (incremented within a stream) for AES in CTR mode. How many different key streams can I produce with this setup?
2
votes
1answer
1k views

Using “Additional Authenticated Data” as a secondary key

In implementing a cipher in GCM or CCM mode, you are provided the option to add "Additional Authenticated Data" (AAD). This AAD is required for decrypting the cipher text, and seems to be used when ...
2
votes
1answer
1k views

Generating a strong unique Initialization Vector

How can I determine if I am generating a unique and strong Initialization Vector? If my mode is generating Keystream? Is there any scientific explanation in generating a unique and strong ...
2
votes
2answers
230 views

Byte location of plaintext vs ciphertext when using a block cipher or stream cipher

I know that when you use a stream cipher you are just XOR'ing the plain text with the PRNG stream, such that you know if a specific byte is in position 3 of the plain text it will still be in ...
2
votes
1answer
2k views

Use of nonces in Kerberos and Needham–Schroeder protocols

Can you please explain me what is the reason of using nonces in the Needham-Schroeder and in the Kerberos protocols for Key Transport. In particular : Can you explain me the use of $N_A$? And ...
2
votes
1answer
264 views

Regarding matsui's Paper on Linear Cryptanalysis of DES

I's going throught the the Paper by Matsui on Linear Cryptanalysis of DES . In that he says $NS_{5}(16,15)=12$ And then in the next paragraph he says considering the expansion and permutation phases ...
2
votes
1answer
236 views

Separate Read and Write Keys in TLS Key Material

Why does the TLS protocol use different symmetric keys for receiving and sending data? Isn't it enough to have a single key used for both reading and writing?
2
votes
1answer
217 views

Transparent cipher

I'm trying to implement this protocol: Alice has her permanent key $K_1$. She computes $E(K_1, P)$. She wants to share $P$ with Bob, Carol and Dave. For each of them she: 2.1. Generates $K_2$. ...
2
votes
2answers
105 views

Encrypting documents through a proxy key

Suppose I'm developing an app to secure a lot of documents. These documents were encrypted (say, using AES) with a key X. This key X is basically the password that the user enters before wanting to ...
2
votes
1answer
818 views

Recovering the key in an ElGamal Signature Scheme variant

From page 318 in Stinson's "Cryptography: Theory and Practice", question 7.3: Suppose that Alice is using ElGamal Signature Scheme. In order to save time in generating >the random numbers k that ...

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