The semantic-security tag has no wiki summary.
6
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1answer
124 views
Message space in security definitions
What is the message space in the following example and how does a message space relate to a security definition?
I mean, what difference does it make to such a definition if your message space is ...
5
votes
2answers
301 views
Practical necessity of semantic security under chosen plain text attack (CPA) in CBC mode
I was not able to understand why we practically need a CPA security in Cipher Block Chaining. (which insist on having a random IV), let say if the encryption is not CPA secure i.e , the adversary can ...
4
votes
3answers
211 views
Is there a public key semantically secure cryptosystem for which one can prove in zero knowledge the equivalence of two plaintexts?
If Alice encrypts two messages $a$ and $b$, such that $x=E(a)$, $y=E(b)$. Can Alice prove (without revealing $a$, $b$ or the private key) that $a = b$?
Obviously the proof must not be too long and it ...
2
votes
2answers
246 views
Can I build a secure tweakable block cipher from a normal one by adding key and tweak?
Let (E,D) be a secure block cipher.
Consider the following tweakable block cipher:
...
2
votes
2answers
137 views
Which categories of cipher are semantically secure under a chosen-plaintext attack?
I am trying to get my head around the circumstances under which a cipher is (or is not) semantically secure under a chosen-plaintext attack.
I can't seem to find a good reference explaining this.
I ...
1
vote
2answers
102 views
Is semantic security important in a hybrid cryptosystem?
RSA doesn't provide semantic security when used unmodified, and neither does the commonly used PKCS#1 v.1.5 padding scheme for encryption.
Is this a problem for hybrid cryptosystems at all?
My ...
1
vote
1answer
142 views
Can a shift cipher attain perfect secrecy?
On a practice question for my intro cryptography exam, it asks the following:
Assuming that keys are chosen with equal likelihood, the shift cipher provides:
A) computational security
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1
vote
1answer
113 views
Constructing secure key exchange protocol
I have $\Pi=(Gen,Enc,Dec)$ and let it be semantically secure public-key encryption scheme. Security parameter is $n$, then the message space of plaintext is always $\lbrace 0, 1 \rbrace^n$.
By using ...
0
votes
1answer
117 views
Why is proof-by-reduction needed (for Elgamal proof of security, for example)?
The textbook proof for Elgamal encryption basically reduces to the Decisional Diffie-Hellman assumption (DDH).
Elgamal:
$Gen(.): x \xleftarrow{R} \mathbb{Z}_p$; $Enc(m,g^x): r \xleftarrow{R} ...
