Questions about formal definitions of "security" for various cryptographic schemes (e.g. perfect secrecy, semantic security, ciphertext indistinguishability, etc.)

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How exactly is “true randomness” defined in the realms of cryptography?

Especially in relation to stream ciphers, I frequently read about (sometimes theoretical, sometimes practical) attacks that are able to "distinguish a ciphertext from a truly random stream". What's ...
9
votes
1answer
2k views

What stops the Multiply-With-Carry Random Number Generator from being a Cryptographically Secure Pseudo-Random Number Generator?

Despite the fact that Marsaglia's MWC PRNG (multiply-with-carry random number generator) is considered to be "the mother of all RNGs", it does not seem to be considered to be a CSPRNG ...
3
votes
2answers
399 views

Definition of a CSPRNG

I am interested in what conditions are necessary and sufficient to define a cryptographically secure pseudo-random number generator (CSPRNG). Wikipedia lists two defining characteristics: It ...
2
votes
2answers
369 views

Why is a non fixed-length encryption scheme worse than a fixed-length one?

I have the following definition (highlights by me): An (efficient secret-key) encryption scheme $(Gen,Enc,Dec)$, where $Gen$ and $Enc$ are PPT algorithms and $Dec$ is a Deterministic Polytime ...
7
votes
2answers
172 views

Key Size for Symmetric Homomorphic Encryption Over the Integers

In the paper Fully Homomorphic Encryption over the Integers, it mentions a symmetric key scheme on page 1 and 2. Key Generation: Pick a random odd number $p \epsilon [2^{N-1},2^N)$ Encrypt A Bit m: ...
6
votes
1answer
277 views

Understanding Twist Security with respect to short Weierstrass curves

I'm trying to understand the "Invalid-curve attacks against ladders" section of SafeCurves Twist Security page and I have difficulties to apply it to short Weierstrass curves. That section claims ...
3
votes
1answer
371 views

Proofs of security methodologies

I'm looking for course material on the subject of proofs, reductions, and games, as used to prove cryptographic schemes secure. What are the methodologies? What are the preferred ones? In what cases ...
4
votes
2answers
358 views

Block Ciphers and (Non-)Generic Attacks

I am currently reading through Cryptography Engineering and came across this definition of block cipher security: Definition 2 An attack on a block cipher is a non-generic method of ...