2
votes
1answer
305 views

Shamir's secret sharing with passwords

I'm trying to design an extension to Shamir's Secret Sharing that would allow the participant to specify a password instead of remembering/storing a large integer or binary data. So far, I have two ...
2
votes
1answer
899 views

What key exchange do OpenSSL and CryptoAPI prefer by default?

Here is what I know. When I connect to a brand-new Linux Web server with Chrome and click the "lock" icon, the key exchange algorithm is described as "ECDHE_RSA". (Yes I know what that is.) When I ...
2
votes
1answer
273 views

The security of an encrypt-and-MAC

I would like to know what is the security of an encrypt-and-MAC with different keys for each transaction For example: the one-time-pad with $k_1$ and the HMAC with $k_2$ $$C = M \oplus k_1\\ MAC = ...
2
votes
1answer
346 views

Proof of correctness of a homomorphic ElGamal sum

Let's suppose we are using the exponential ElGamal as a public-key encryption scheme, so that we encrypt $g^m$ instead of $m$, for some generator $g$. Let $x$ be the private key, and $h=g^x$ be the ...
2
votes
1answer
196 views

RC4 system pitfalls

A system fell into my neck, where lots of files are splitted into several segments and encoded via RC4. RC4, because client side - slow computer, slow flash arithmetic ops - can only decode big blobs ...
2
votes
1answer
153 views

Multiple parties must encrypt and get the same result

Hopefully this question is not too simple - I did some research but with encryption I really don't want to make a mistake. Our scenario is that multiple groups need to encrypt a number and arrive at ...
2
votes
1answer
658 views

How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
2
votes
1answer
165 views

Verify Messages to Embedded Device

I'm building an embedded device that I plan on distributing. Periodically the device will poll my server to check for updates and commands. I'd like the device to verify that any messages(JSON strings ...
2
votes
2answers
170 views

Does it necessarily mean that an RSA moduli generated with poor randomness is not random?

In 2012 a group of researchers collected a large amount of RSA moduli and calculated their greatest common divisor in order to find common factors between them. By finding a common factor they could ...
2
votes
2answers
684 views

Derive a key from public data using a secret master key

Users in my system will be given a device that contains a 128-bit AES user key. The user key will be derived from 64 bits of public data related to the user, which is unique but very predictable (i.e. ...
2
votes
2answers
148 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
588 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
367 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
291 views

The probability of finding a limited set of collisions for HMACSHA256

I need some input on the use of HMAC-SHA256 in an open source project, any help appreciated. The problem I'm solving is session fixation. We have a username, for that username we'd like to generate a ...
2
votes
1answer
245 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
827 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
82 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
1answer
1k views

How is text converted to a number for RSA? [duplicate]

According to http://en.wikipedia.org/wiki/RSA_%28algorithm%29#Key_generation the key length is the number of bits in n. So how can a message of many megabytes (millions of bits) be modded by a 1024 ...
2
votes
2answers
432 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
350 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
164 views

Connections between Instance Hiding and Fully Homomorphic Encryption

Another approach taken by researchers for carrying out computations over encrypted data is Instance Hiding. In brief, If a user wants to outsource the computation of a function for a particular input ...
2
votes
1answer
245 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
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
636 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
305 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
105 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
404 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
575 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
567 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
1answer
92 views

Could use an explanation of the notation for an oracle adversary

In the definition below, what exactly does it mean for the adversary (not even sure that's the correct term?) to equal one? $$ \underset{K}{Pr} \left [A^{F_k(\cdot)} = 1 \right ] $$ Source (Page ...
2
votes
2answers
198 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
125 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
95 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
2answers
270 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
573 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
935 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
232 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
409 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
998 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
466 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
2k 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
2k 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
326 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
963 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
400 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
226 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
279 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?

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