Linked Questions

31
votes
2answers
8k 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, ...
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-* ...
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 ...
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 ...
7
votes
3answers
327 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
333 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 ...
6
votes
2answers
450 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
1answer
312 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 ...
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 ($E(A)$ ...
4
votes
2answers
282 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 ...
4
votes
1answer
288 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 ...
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?
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
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 \...

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