-1
votes
1answer
54 views

How ECDH algorithm selects modulus value?

I am curious to know how an ECDH algorithms select a module value, if both ends A & B can generate same shared key using the public key of each other ? If I understood DH correctly, both A and B ...
2
votes
1answer
117 views

Why isn't a table used to solve the large number factoring problem?

Lots of modern encryption (RSA comes to mind) are based on the fact that factoring large numbers is hard. However, multiplying large numbers is much easier, and table lookups are very easy. Since ...
2
votes
1answer
72 views

What is this encryption system called?

Let's say you want to break down a message, for simplicity it is just a bit $0$ or $1$, $m$ into two messages $(m_1, m_2)$ as follows: If $m =0$, then $(m_1, m_2) = (0, 0)$ with probability $1/2$ and ...
3
votes
1answer
187 views

public key cryptography and authentication for cross-platform network application

I'm developing network based application for control and telemetry on Linux based embedded system. I'm using ZMQ network library and Google Protocol Buffers serialization library for communication ...
2
votes
0answers
44 views

Testing PRNG quality from ECC public keys?

Having a large set of ECC public keys $P_i = n_iB$ on a fixed curve $E$ over a prime field, is there a way to determine if coefficients $n_i$ were generated using a bad PRNG? In other words, can a ...
8
votes
4answers
1k views

Is it possible to get an RSA encryption key by comparing the unencrypted and encrypted file?

Exactly what the title says. If I have a RSA encrypted file, and the exact same file but decrypted, can I tell the key that was used from that information?
1
vote
1answer
99 views

File encryption with AES CTR mode

I understand that encrypting files in CTR mode is not perfectly safe, because it potentially leaves the files open for cryptanalysis, if the attacker has access to previous versions of the same files. ...
2
votes
1answer
61 views

Strong LRSW assumption for type 3 pairing groups

Why does the "strong LRSW" assumption by Ateniese et al. [Untraceable RFID Tags via Insubvertible Encryption, CCS'05] hold ONLY for type 3 pairings and NOT for symmetric pairings? Whereas, the LRSW ...
7
votes
2answers
356 views

Is calculating HMAC from hashed input a good idea?

Original HMAC algorithm is as follows: H(K XOR opad || H(K XOR ipad || text)) What if text would replaced with H(text)? ...
4
votes
1answer
138 views

Usage of Zero-knowledge proofs for NP-complete languages

It is well known that if OWFs/PRGs exist, then there is a zero knowledge proof for any NP-complete language, say G3C (graph coloring in 3 colors). The zero-knowledge notion maintains that any ...
3
votes
1answer
55 views

Prove that H(s) = G(!s) is a CPRNG if G(s) is one

Given a cryptographic pseudo-random number generator $G$, prove that $H$ with $H(s) = G(!s)$ is also a cryptographic pseudo-random number generator. Here $s$ is a binary string; $!s$ is its ...
7
votes
2answers
209 views

How does the simulator of the special-honest verifier zero-knowledge property works?

I’m a bit confused about what the simulator of the special-honest verifier zero-knowledge property of a $\Sigma$-protocol is supposed/allowed to do and how to prove that it is indeed efficient (i.e. ...
2
votes
1answer
154 views

Extension of a password hashing algorithm using Fibonacci

I am right now taking a class named Applied Cryptography and our final project is to create a password hashing method using at least one existing algorithm and then add additional steps to make it ...
5
votes
2answers
671 views

How to verify the integrity of RSA encrypted messages?

I need to encrypt messages using PublicKeyCrypto and send it to the server, where the message should be decrypted. I'm aware of the Padding Oracle Attack and want to apply a server side integrity ...
12
votes
3answers
4k views

Why is the P-521 elliptic curve not in Suite B if AES-256 is?

In the NSA's document, "The Case for Elliptic Curve Cryptography" (archived), we have ...
4
votes
1answer
506 views

Understanding a Blowfish cryptanalysis

I'm reading a cryptanalysis on Blowfish, and I've come across something that I don't quite get. Let's denote $$\delta = a \oplus a'$$ where a and a' are bytes that cause a collision in some S-box ...
1
vote
1answer
68 views

Are digital signatures using preprocessed paper pads possible?

My idea was, given that a computer could produce some sort of lookup tables on paper, could then a human use those lookup tables to create a system for digital signatures? This was really an idea for ...
0
votes
0answers
32 views

how many pairs of plaintext-ciphertext are needed before we break AES? [duplicate]

Imagine a set of words ($plaintext$) each are encrypted using AES-ECB mode and due to some leakage in the system an attacker could gain access to some pairs of $plaintext$ and $ciphertext$. But once ...
16
votes
2answers
18k views

HMAC-SHA1 vs HMAC-SHA256

I have three questions: Would you use HMAC-SHA1 or HMAC-SHA256 for message authentication? How much HMAC-SHA256 is slower than HMAC-SHA1? Are the security improvements of SHA256 (over SHA1) enough ...
5
votes
0answers
110 views

Would the encryption of bigrams and trigrams weaken the code?

Supposing a rotor machine of the 1940s or 50s, with 36 characters instead of 26. Would the encryption of the ten additional characters as the most frequent bigrams or trigrams weaken the code? What ...
1
vote
1answer
117 views

Cryptography in wireless medium

How do I implement asymmetric key algorithm into wireless medium using NS 2.35? For example: node $A$ is a sender and $B$ is a receiver. Now, $A$ is sending a packet using $B$s public key ...
1
vote
2answers
78 views

Collision probability of MD5 over different attacks

I am researching the collision probability of MD5 and various attacks against it. Can someone help me how to learn the least probability that there will be a collision in a specific attack on MD5? ...
6
votes
3answers
136 views

Why is it good to split a CTR-mode counter into nonce and counter?

When discussing the CTR mode of block ciphers, Wikipedia says the following: Simply adding or XORing the nonce and counter into a single value would completely break the security under a ...
1
vote
2answers
113 views

Perfect secrecy with n-time key

How can you encrypt $n$ messages with the same key, and have the same theoretical security you'd have encrypting a single message with a one time pad? For example, how can you encrypt two messages ...
4
votes
1answer
417 views

How hard is the Solitaire cipher to crack?

Assuming your deck is completely random and that it is not retrivable, how hard would it be for a casual person to decrypt a message encrypted with the Solitaire cipher?
4
votes
2answers
324 views

Why must we generate the signature before any compression being done at PGP?

I have done some research on PGP and I found out there are of two reasons why we must generate the signature before doing any compression. Yet, I am not sure I really understand them both. One ...
3
votes
1answer
144 views

Is RSA vulnerable to the padding oracle attack?

I know that AES in combination with CBC mode is vulnerable against the Padding Oracle Attack. RSA also uses some kind of padding, hence can this attack be apply to RSA encrypted messages too?
10
votes
3answers
888 views

How useful is NIST's Randomness Beacon for cryptographic use?

NIST have just launched a new service called the NSANIST Randomness Beacon. It has been met with some initial skepticism. Perhaps the cryptography community would have used it before June 2013 when ...
2
votes
1answer
92 views

Mathematically / statistically “safe” way to differentiate between crypto and random blob?

I assume the United Kingdom will impose (as opposed to just talk about it) restrictions on crypto software that may be used within it's borders. Me, quite the border clown (yes, I always bring a up ...
5
votes
1answer
125 views

EC: Why does $h>200$ need to hold?

From BSI-TR-03111 (PDF), on page 15: The class number of the principal order belonging to the endomorphism ring of E SHOULD be at least 200. This value commonly is referred to as $h$ in that ...
1
vote
0answers
52 views

Details related to the ZIP algorithm used in PGP message encryption? [closed]

I am very new to PGP. PGP encryption works with hash function, asymmetric encryption, symmetric encryption and a zip algorithm (LZ77). What I know is that the zip algorithm is used to reduce the ...
1
vote
1answer
77 views

Anonymous offline digital cash scheme

Can a digital cash scheme exist that is anonymous and offline using blind signature and anonymous signature?
11
votes
2answers
219 views

Attacking RSA signature verification that ignores padding

I am looking at a RSA signature verification that is quite obviously flawed and am wondering if there's a way to exploit that flaw in practice. Signature is generated using RSA with PKCS 1.5 padding, ...
2
votes
2answers
67 views

How badly does disclosing an M-bit prefix of an N-bit private key compromise security?

I apologize profusely for knowing nothing about cryptography, please go easy on me! I'm working on a project where I have a 2048-bit RSA private key and a public certificate generated from the ...
1
vote
2answers
239 views

Attribute-based encryption for cloud storage

I'm trying to understand attribute-based encryption schemes. Almost all articles describe that they are designed for cloud storage, but as I understand, almost all computing (encryption & ...
1
vote
1answer
84 views

Is it a good practice to use plain text for derivation of Keys?

I have a question regarding the derivation of keys in crypto. Is it a good practice to use the plain text (in form of hashes) for derivation of keys ? these keys will be used for encryption of the ...
3
votes
1answer
63 views

Given just the hash of a file, can I verify that the file contains a specific data block?

Imagine I only have the hash of a file which we can call hash(file). Then a user sends me a data block (or section) of the same file, which we can call ...
4
votes
1answer
632 views

Attacking historical ciphers methodology

It's more a theoretical question of how would you approach it. All you know about the ciphertext it's was generated with a historical cipher. The ciphertext appears to be random, BUT it's divided into ...
1
vote
2answers
44 views

Validate per round rather than cycle-walking in FPE

I was thinking about FPE specifically for numbers, CC, phone, SS #, etc. and I thought of some small "optimization" that could be implemented. Can I validate the string length after each round in the ...
3
votes
1answer
221 views

Why don't we use bcrypt and scrypt together?

Everyone is comparing bcrypt to scrypt. Bcrypt is proven, lots of cryptoanalysis and no vulnerabilities so far, but uses very low memory. While scrypt uses a lot of memory, but it's too early in its ...
6
votes
1answer
378 views

What does “a 15360-bit RSA key is the equivalent to a 256-bit symmetric key” mean?

NIST key management guidelines suggest that 15360-bit RSA keys are equivalent in strength to 256-bit symmetric keys. If a 15360-bit RSA key is the equivalent to a 256-bit symmetric key, does that mean ...
6
votes
4answers
361 views

Why aren't zero-knowledge proofs used for authentication in practice?

I read on Wikipedia that zero-knowledge proofs are not used for authentication in practice. Instead (I think) the server is entrusted with seeing a password in plaintext form, which it should then add ...
3
votes
1answer
131 views

Secure method of encrypting data within a database

I'm designing a program which makes queries to a database stored locally which could potentially contain a lot of sensitive information. As such the information must be kept secure as possible from ...
2
votes
2answers
91 views

Same 64-bit preimage resistance security for SipHash and SHA-512/64?

If I have to chose a 64 bit preimage resistant hash function; will there be any difference in security between SipHash and SHA-512/64 (SHA-512 truncated to 64 bits)? How long will it take an ...
14
votes
2answers
519 views

Is (AES-)GCM parallelizable?

I recentely faced the issue of random access decryption while AES-GCM was being used. I said this person that the underlying CTR should allow parallelization but I have no idea how authentication ...
2
votes
2answers
89 views

What kind of operations are involved in NTRU?

I've read that lattice based algorithms involve matrix-vector products. Is this the case of the NTRU algorithm? When I've read the details of the NTRU algorithm, I've seen products of polynoms. Where ...
3
votes
1answer
156 views

Is there a scheme that allows to use RSA based challenge response protocol limited to signing only 8 bytes to create a secure signature of any data?

I have a tiny device that has a challenge-response authentication mechanism where the device signs 8 bytes of any data with it's internal 2048 bit RSA key. I would like to be able to certify any data ...
0
votes
1answer
93 views

What is the meaning of h(r) in this protocol?

Could somebody tell me what the meaning is of $h(r)$ in the protocol below? ‎‎$A‎\leftarrow‎{B}\quad:{h(r)‎‎}{,B}{,P{_A(r,B)}}‎ \\A‎\rightarrow‎{B}\quad:r$
3
votes
1answer
273 views

Standard format to encode AES cipher and random IV

As far as I understood, a secret key (same length as CBC block size) and an initialization vector (IV) are needed to decrypt a AES-256-CBC encrypted string. As the IV should better be random, it has ...
4
votes
0answers
91 views

Is the key schedule of Serpent a circle?

The creation of the prekeys for Serpent works by XORing some previous values with a counter and a fixed value. Every word is 32 bits big and 4 words form a round key (after applying a S-Box, but this ...

15 30 50 per page