# All Questions

181 views

### Why don't use random padding in RSA?

Consider the following scenario: Sender S sends a message to receiver R. He uses a hybrid encryption scheme with RSA as key-encapsulation algorithm and AES-256-CTR (4byte-counter) and SHA256-HMAC. ...
378 views

### Why should one prefer Salsa20 over ChaCha?

We are all aware of Google's approach to introduce ChaCha/Poly1305 as TLS cipher suite. The rationale seems clear: ChaCha is newer and seems to provide better security (and maybe speed?) gained from ...
247 views

### Simulation based proofs: Simple examples

I am aware that,(in theory) in order to proof that a scheme is secure using simulation based proof we replace an adversary in real world with a simulator in ideal world. Then we try to show that their ...
309 views

### Has anyone heard of matrix-based “Russian Doll” encryption techniques?

I've been told that prime-number factoring is based on a "russian-doll" sequence of matrices, where a seed matrix of height Y and width X exists consisting of all zeros except for a single 1 at row Y ...
184 views

### What values constitute failing for ENT tests?

The dieharder tests give a clear PASSED, WEAK, etc and I'm wondering what those thresholds ...
262 views

### ElGamal and Paillier key sizes for short messages

I am using ElGamal and Paillier schemes to encrypt a large number of short messages: typical 4-byte integers. I do this for the homomorphic properties of these schemes. However, the way the ...
214 views

### 64bit nonce in AES-CTR, why not 128?

I'm just a bit confused about the nonce/IV in AES-CTR ... it seems the suggested way to go is have a 64bit random nonce, and use the last 64bits as the counter, "starting at 0". I'm just wondering ...
168 views

### Determine AES key given encrypted and unencrypted files

Given an encrypted file, the original unencrypted (cleartext) file, and knowledge of which AES encryption algorithm was used, is it possible to determine the key that was used to encrypt the data in a ...
599 views

### Why does “2xAES-256” provide “99.99%” security strength whereas “1xAES-128” provides “40%”? [closed]

I recently was "directed" to FlipsCloud, a company selling security solutions (as far as I can tell). In particular I've investigated their page and found a page on their "encryption features". This ...
59 views

### Identification schemes: Okamoto

I am reading Cryptography theory and practice by Stinson. The book is talking about the proof of security of Schnorr and Okamoto schemes. It claims that if an impersonater can find (in the case of the ...
80 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? ...
121 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 ...
77 views

### Why does encryption in STS protocol protect against identity attacks?

The basic STS protocol contains encryption of the signature as shown in Wikipedia. https://en.wikipedia.org/wiki/Station-to-Station_protocol If we would like to defend against MITM attack, this ...
152 views

### Blowfish Weak keys

I've read about the weak key issue with Blowfish, but can't seem to find anything that explains the practical effect of weak keys on Blowfish with the full 16 rounds. Is there any actual attack upon ...
95 views

### What needs to be proved for a cryptosystem to be secure?

For example showing that it is easy to produce ciphertext from plaintext but is difficult/impossible to get plain text from ciphertext. I am asking in general but am more interested in asymmetric ...
169 views

### Deterministic ECDSA signatures?

ECDSA signatures depend on parameter k that is chosen by the signer. As a result, there are many signatures for the same private key d and message m. What I want to achieve is a deterministic ...
143 views

### How many bits to flip in an RSA public key to do signature forgery?

Scenario: Alice wants to verify a signature from Bob. Alice knows Bob's RSA public key (e, n). However, Alice is getting the data, the signature of the data and the public key from an attacker Eve. ...
122 views

### Problems implementing AES in CBC+CTS mode

I'm trying to implement an AES cipher in CBC+CTS mode, but I'm unable to get the second last plaintext block to decrypt properly. I've attached my code, it's based on the steps listed under CBC ...
68 views

### Is authenticated encryption basically a lockable box?

I recently used a custom construction as a commitment scheme, which was taken from the standard picture you give people while explaining commitment schemes. Basically commitment schemes can be ...
46 views

### One-Time-Signature based codes

I'm trying to understand the sentence in bold, in the follow paragraph of A new one-time signature scheme from syndrome decoding Keygen: Given a security parameter $\lambda$, choose a suitable ...
163 views

### How to derive the curve Ed25519 from Curve25519?

According to the paper "Faster addition and doubling on elliptic curves" by Bernstein and Lange, the Montgomery curve (Curve25519) $$v^{2}=u^{3}+486662\cdot u^{2}+u$$ is birationally equivalent to the ...
60 views

### Certificate for the public key

I am new to Network Security and learning about various security features like Diffie-Helmann and others. I understand that the Public key send by the server to the client needs to certified that it ...
116 views

### curious DHE implementation for key exchange

I have made some reverse engineering on proprietary software and came up with some DHE algorithm that works like this: First and foremost, the client and the server shares some public parameters (g, ...
136 views

### MAC tag size in AES CCM, when using CTR + CBC-MAC (not CBC MAC only)

Assuming that AES CCM is used with respect of the NONCE unicity // the key life cycle, I wonder about the need of using the highest size for CBC-MAC authentication tag if CTR mode encrypts both ...
60 views

### Unconditional authentication

I have a few questions regarding universal-hash functions: Is there a way universal hash functions can be used to provide unconditional authentication in the way the OTP provides unconditional ...
42 views

### N users must approve a request

I have a locked-down production system that we'd like to process specific requests, picked-up (poll) from a less-secure location. For security and "go slow, this is production" reasons, a request ...
87 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 ...