# Tag Info

Accepted

### What is the difference between uniformly and at random in crypto definitions?

If you sample a random element, then you sample it according to some distribution. Uniformly then means that you sample from the uniform distribution, i.e., you sample it from a set where drawing ...
Accepted

Accepted

### An unpredictable PRG is secure (Theorem Yao'82)

This lecture (PDF) has the solution in section 3. Here's my informal explanation of the proof: We have an unpredictable PRG $G$. We want to show that $G$ is secure, or in other words ...

### Key Size for Symmetric Homomorphic Encryption Over the Integers

The paper says that the parameters are $r ≈ 2^{\sqrt \eta}$ and $q ≈ 2^{\eta^3}$. Note that these values are expressed as functions of $\eta$, not $N$. With regard to the parameters, it is common ...
Accepted

### Does information theoretical security definition imply DDH, RSA, QR does not hold?

Does this mean that the standard definitions for DDH, RSA or QR do no hold in that setting, because the definitions assume some bounds on the computational power of the adversary? That is correct; a ...
Accepted

### Does GCM (or GHASH) only provide 64-bit security against forgeries?

The phrase ‘128-bit security’ is a bit glib to cover the online/offline distinction—the purpose of the explicit formulas is to quantify the forgery probability in terms of limits on the online and ...
Accepted

### What is the difference between information-theoretic and perfect types of security?

Information-theoretic security means that any algorithm (even unbounded) has a negligible probability of breaking the security property (in the security parameter). This is the same as unconditional ...

### What is the security concept in printer cartridge?

A company can make more money if the printers it sells only work with the cartridges they sell, which does not work if there is competition. It's cheaper to force a vendor lock-in than it is to ...

### Simply put, what does “perfect secrecy” mean?

Perfect Secrecy essentially means these notions: $P(M=m|C=c) = P(M=m)$ i.e. seeing a ciphertext doesn't give you any extra information about the plaintext. The probability of seeing a message $m$ ...
Accepted

### Is the practice of "security through obscurity" violating Kerckhoffs's second principle?

"It should not require secrecy, and it should not be a problem if it falls into enemy hands" Where "it" is the algorithm design itself, and not an input to it... But isn't the practice of ...
Accepted

### Indistinguishability of symmetric encryption under CCA

CCA security always seems extreme to people who are just learning about it. The premise seems ridiculous, why would we give the attacker so much power? Why would we just let the attacker decrypt ...

### Simply put, what does “perfect secrecy” mean?

Perfect secrecy is the notion that, given an encrypted message (or ciphertext) from a perfectly secure encryption system (or cipher), absolutely nothing will be revealed about the unencrypted message (...
Accepted

### Effective security of block cipher – equal the key size, or half the key size?

I just read that chapter of the book, and the authors don't really justify their claim. They also talk about "using random data to prevent collision and precomputation attacks" (which would then give ...
Accepted

### Key Size for Symmetric Homomorphic Encryption Over the Integers

-- Introduction First of all, I know that you are trying to have a better understanding about the symmetric scheme, but, since the authors focused on the public key scheme, you will have to ...
For convenience, let's assume that $\mathcal{K} = \mathcal{D}$ so that the key $k \in \mathcal{D}$. Define $E$ to be some strong PRP, and let $D$ be its inverse. Now, define a PRP \$E' : \mathcal{D} \...