Linked Questions

2
votes
1answer
3k views

What is the meaning of IND-CCA secure under standard model? [duplicate]

I notice that in many research papers (viz. "Universal hash proofs and a paradigm for adaptive chosen ciphertext secure public-key encryption" by Cramer and Shoup) the authors showed that their ...
1
vote
0answers
694 views

Understanding CPA and CCA Secure [duplicate]

CPA attack means the attacker can send in his own plaintext to the oracle and receives some sort of ciphertext back. CCA attack means the attacker can send in his own ciphertext to the oracle and ...
1
vote
0answers
361 views

What do you mean by Ciphertext indistinguishability [duplicate]

Wiki definition : A cryptosystem is considered secure in terms of indistinguishability if no adversary, given an encryption of a message randomly chosen from a two-element message space ...
31
votes
2answers
7k views

7zip : Why does encrypting the same file with AES-256 not give the same output?

Using 7-zip 19.00, on Windows 10 1909, build 18363.592, I encrypted a text file with the contents "hello there" using AES-256 and the password "123". I did this two times, the exact same procedure, ...
11
votes
5answers
2k views

What is the purely mathematical definition of encryption strength?

An encryption function can be used to obfuscate pieces of information and later on retrieve them. What is the yardstick for measuring how well the function encrypts the information ? Given any ...
19
votes
1answer
4k views

What do the signature security abbreviations like EUF-CMA mean?

From time to time, one stumbles across formal security definitions. This includes security definitions for signature schemes. The most common ones are the *UF-* ...
8
votes
1answer
2k views

How to prove security of a randomized encryption algorithm?

I have designed an random encryption in public key setting. I am convinced about its security guarantee but I need a formal way to prove its robustness. How can I prove the security of this random-...
7
votes
3answers
2k views

Does adding complexity mean a more secure cipher?

I have a cryptography workshop question I'm having trouble with as follows; Person A creates a cipher $E_k(m)$ which produces a ciphertext from message $m$ using key $k$. The function inside $E$ is ...
1
vote
5answers
11k views

How secure is a client-side javascript encrypter?

A friend of mine needed help with her website and asked how to send me her login information securely. I've never known how to do this, so I figured now was the time to learn. After some googling, I ...
3
votes
3answers
2k views

How can a system be non-deterministic?

Newbie here, so forgive me if this is a stupid question. In math class we learned about RSA encryption (as a practical application of what we learned about the Euler phi function and Fermats little ...
3
votes
2answers
1k views

Does having a hash of the plaintext compromise the ciphertext?

If I have a SHA512 hash of my plaintext, does it weaken or break the encryption of my ciphertext?
5
votes
1answer
2k views

Is ElGamal IND-CCA1?

We all know that textbook ElGamal falls due to chosen ciphertext attacks, because of its multiplicative homomorphic property ($E(A)*E(B)=E(AB)$). However these attacks require the ciphertext ($E(A)$ ...
3
votes
1answer
3k views

ElGamal CPA secure

I understand that if DDH (Decisional Diffie–Hellman) is hard then ElGamal is CPA secure. But I'm having confusion on what part the DDH applies to. So, given $pk=(G, g, y), y=g^x$ and $sk=(pk,x), x \...
2
votes
3answers
741 views

Can public key help attackers to break RSA encryption faster?

I have two, closely related questions: Can a really good attacker (hacker) use the public key for his advantage and break RSA encryption faster? My point is that in RSA "communication" public key is ...
7
votes
3answers
319 views

Is there a cryptographic approach to availability

Background Cryptography can be said to provide the tools used to fulfill the goals of information security. The three pillars of information security are confidentiality, integrity, and ...
6
votes
2answers
415 views

What do NM-CPA, and NM-CCA mean?

When I've been researching authenticated encryption, the following terms keep showing up: NM-CPA NM-CCA ....without any definition as to what they mean. I've tried searching the web for their ...
6
votes
2answers
312 views

Why does Encrypt-Then-Sign not yield a CCA-secure public-key encryption scheme?

In symmetric cryptography, combining an IND-CPA secure symmetric encryption scheme with a secure MAC with the encrypt-then-MAC method yields a IND-CCA secure symmetric encryption scheme. I am trying ...
4
votes
2answers
279 views

Chosen plain text and chosen ciphertext definitions clarification

I am trying to understand a concept of CPA and CCA attack and I cannot get one thing from the definition. If an attacker can execute a CPA attack for something like Send 100 dollars to attacker that ...
2
votes
1answer
456 views

Homemade Randomized RSA

Considering the following encryption scheme where RSA is used to encrypt a plaintext m and then we choose a random r and compute: $$A = r + m^e \bmod N$$ and $$B = r^e \bmod N$$ So the ciphertext is ...
0
votes
1answer
161 views

Is there any theory to measures and determine the strength of an encryption protocol?

To determine the strength of an encryption protocol, there are elements like key size, Strength of an algorithm, Performance of an algorithm or etc, I have studied these topics but I could not find ...
1
vote
1answer
712 views

Padding on RSA signature and RSA encryption

Why use a random padding on RSA encryption and not on RSA signature?
5
votes
1answer
288 views

Which attacks are possible against raw/textbook elliptic curve?

A quick question, we know that raw RSA is a no go. To solve this we have different PKCS standards forcing structure on the input messages. For EC the story is something else. For signatures we have ...
0
votes
1answer
283 views

Use of OAEP in RSA Encryption

I am working on creating an RSA Algorithm and learned that OAEP is a padding scheme that is commonly used before encrypting using RSA. Is this step necessary? Will it harm the integrity/security of ...
4
votes
1answer
272 views

Does Elliptic Curve Integrated Encryption Scheme (ECIES) provide IND-CCA2 security?

I am looking for a faster alternative to RSA with OAEP as a IND-CCA2 public key scheme. Elliptic Curve Integrated Encryption Scheme might be a candidate, but I am not sure if it provides IND-CCA2 ...
0
votes
2answers
228 views

What type of encryption is this homebrew “encyption algorithm”? ${}$

Background: Quite a long time ago (somewhere 1998) I thought I was really clever and invented my own encryption/decryption code. Looking through old code I rediscovered my old algorithm. (No, it was ...
0
votes
1answer
276 views

When do I need to use hybrid cryptography?

I need to provide confidentiality for a protocol. The protocol message size is between 100 bytes to 500 bytes. Do I need to use asymmetric encryption or hybrid cryptography?
0
votes
1answer
418 views

Message Expansion / Encryption Blowup Factor / Ciphertext Expansion of ECC

In order to complete the following table with asymptotic times and message expansions, $\quad \quad \quad \quad \quad \quad \quad \quad \quad$ RSA $\quad$ McEliece $\quad$ ECC Encryption Speed $\...
3
votes
1answer
193 views

Can you help me understand indistinguishably as described in the CPA security definition?

When I read the definition of the CPA indistinguishably encryption scheme, I see that the adversary can use an oracle as many times (to get as many encryptions of any messages it choose). An the end ...
0
votes
1answer
307 views

Proof that a modified public-key encryption scheme is not CCA secure

Let $\mathcal{E} = (G, E, D)$ be a CCA-secure public-key encryption scheme defined over $(\mathcal{M, C})$ where $\mathcal{C} := \{0, 1\}^\ell$. Let $\mathcal{E'} = (G, E', D')$ be a scheme (over $(\...
0
votes
1answer
153 views

Is this a good communication scheme?

I'm writing a wrapper for a chat program to allow for end-to-end encryption. I'm using Python and PyCrypto to accomplish this. I'd like to use a well known library to do this, but to my knowledge, ...
1
vote
1answer
83 views

Why can´t an attacker find the key if he has the plain text, the IV and the ciphertext? [duplicate]

I am reading a book about web security and they are now talking about AES CBC. After reading the chapter I was wondering, can an attacker compute my secret key if he has access to the IV, the plain ...
-3
votes
2answers
133 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 ...
0
votes
2answers
117 views

For the symmetric-key encryption algorithm, is it possible to use the exponent and modulo to be the keys

For example: Encrypt with: $M^{k_1} \bmod k_2$ where $M$ is message, $k_1$ and $k_2$ are independent keys If it is possible, what is the decryption algorithm? Thanks!
0
votes
1answer
149 views

algorithmic scheme to compare these two number encrypted using paillier cryptosystem

I have been going through https://eprint.iacr.org/2006/287.pdf (Conjunctive, Subset, and Range Queries on Encrypted Data by Dan boneh) I am trying to implement the paillier system to create a secure ...
1
vote
1answer
85 views

ECDH, x25519 and limitations for securing client-certificates on the server

g'day Crypto.SE I'm working on a practical application of sharing a static key to better-identify a user, between the recipient (server) and the initiator (client ie. user's machine). My core ...
0
votes
1answer
94 views

What is the advantage of a probabilistic PKC over a traditional PKC?

While reading through a textbook, I came across the idea of a probabilistic public key cryptosystem, which uses a probabilistic TM to generate the public encryption and private decryption algorithm; ...
0
votes
0answers
117 views

Formal security-definition reference

Is there a reference where all common formal security-definitions are summarized (such as OW-CPA, IND-CPA, IND-CCA1, IND-CCA2, EUF-CMA and so on)? I need a PUBLISHED reference (paper, book) which ...
1
vote
2answers
79 views

Modes of operation that simply uses the tweak of a tweakable block cipher

What is the name of the mode in which we simply change the tweak for each block without the need for complex chaining modes? Is this mode secure? Are there any other recommended modes for native ...
0
votes
2answers
61 views

would this be classed as a cipher text attack?

Say i'm given a cipher text to decrypt, however i also have access to a server that performed the encryption; where i could enter any plaintext and observe the result of encryption. would it be ...
2
votes
0answers
67 views

Asymmetric encryption property required in an authentication protocol

We want to choose an asymmetric encryption scheme for use as follows: A device holds its private key, with the corresponding public key known and trusted by all. The device also holds a small $b$-bit ...