Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.

# Questions tagged [pseudo-random-function]

A pseudo-random function (PRF) is a family of deterministic functions indexed by a parameter, such that a randomly selected instance is computationally indistinguishable from a uniformly random function with the same input and output spaces.

291 questions
Filter by
Sorted by
Tagged with
108 views
+100

### Any speed up methods for finding the index of a random value produced by the Inversive congruential generator?

The Inversive congruential generator produces random values with: $$x_{n+1} = a\cdot x_{n}^{-1} + b \mod P$$ (special case if $x_n=0$ -> $x_{n+1}=b$) starting with an initial value $x_0$ With well ...
49 views

### Random oracle : Replay

What I understand about the random oracle game: The adversary can query the oracle polynomial many times with the same (secret but unknown) key. From the output returned by the oracle, the ...
64 views

69 views

### Dependence of a Pseudorandom Function's Security on its Input/Output Spaces

Let $n$ be a security parameter and $F:\{0,1\}^{\ell_{key}(n)} \times \{0,1\}^{\ell_{in}(n)} \rightarrow \{0,1\}^{\ell_{out}(n)}$ be a keyed function which forms a family of Pseudorandom Functions (...
6k views

### TLS Key Block calculation - What is a PRF?

In Section 6.3 of the RFC for TLS 1.2, it is written that the key_block is derived from the following formula: ...
90 views

### A hash-based pseudorandom function

Let $H()$ be a cryptographic hash function. Question: Can we consider $c= H(r||i)$ as a pseudorandom value, where $i$ is a public value, $1\leq i\leq n$, and $r$ is a large uniformly random value/...
249 views

### PRF from hash function?

Let $G=\langle g \rangle$ be a cyclic group of prime order $Q$. Let $H_1:\{0,1\}^*\to G$ be a hash function. Is the following a family of PRF for $s \in \mathbb{Z}_Q^*$? $$f_s(x)=(H_1(x))^s$$ Or ...
81 views

### Can you defeat AES-CTR's birthday boundary with a 2nd AES?

This follows on from How do I produce a stream of secure random numbers from AES-Counter mode? Consider then the generator:- $$\operatorname{AES_{k1}}(n) \oplus \operatorname{AES_{k2}}(n)$$ ...
127 views

### PRP vs PRF for the F-function of a Feistel network

A Feistel network is generally defined with a PRF for its F-function, but PRPs have been used as well. What are the theoretical cryptographic implications of using a PRP instead of a PRF? Does it ...
254 views

### Do you really need a KDF when you have a PRF?

My understanding is that a KDF is like a PRF, except that it has a preliminary step that "extract" entropy. It is thus needed when the entropy is non-uniform (for example the output of ECDH is modulo ...
43 views

### PRP, PRF change at next selection?

This is probably a silly question, and similar question was asked before; but I can not figure out what actually is PRP/PRF. For example, it is commented that: A Pseudo Random Function is a ...
66 views

### How does changing input size affect The Goldreich-Goldwasser-Micali Construction?

If we want to construct a PRF that is length preserving, it is easy to show with hybrid proof that the resulting construction is a PRF. But what happens when we have longer input. Supose that the ...
77 views

### Construction PRF from PRG

As discussed here, a classic and secure construction of PRF from PRG is: $F_k(x_1x_2\cdots x_n) = G_{x_n}(\cdots(G_{x_2}(G_{x_1}(k)))\cdots)$ where $G$ is a secure pseudorandom generator. I was ...
97 views

### Does a regularly reseeded PRNG provide backtracking resistance?

I'm currently discussing a security topic with some of my classmates. A cryptographic PRNG typically provides backtracking resistance if an adversary that compromises the internal PRNG state cannot ...
604 views

### Pseudorandom function of different keys

Could someone explain to me how they formulated the equation and how it equals to $0^{n}$ (like what F(x, x) equals to or how they cancel each other out?) on the first box and if its related to the ...
100 views

### A well known hash function?

Name a well-known and standardized function $F : \{0,1\}^{256} × \{0,1\}^{128} → \{0,1\}^{128}$ that is believed to be a pseudorandom permutation. I was thinking SHA256, but I am not sure. Can ...
137 views

### Which functions can be used as Pseudo Random functions? Can block Ciphers be used for this purpose with our own encryption function?

Since the cloud security algorithm I am trying to implement says that for a PRF, any secure encryption algorithm or a keyed hash function can be used. The security parameter I have chosen is 15 bits ...
25 views

### Tool to find non-linearity, resiliency and algebraic degree of a boolean function?

Is there any program or software to find out cryptographic properties like non-linearity, algebraic degree, balancedness and resiliency of a large boolean function?
106 views

### Constructions of PRF (Pseudo Random Function)

I was taught only GGM based PRF construction in class. It's very inefficient. I am just curious about various PRF constructions from standard assumptions. Please provide a few PRF constructions from ...
192 views

### Can Pseudorandom values be used as secure keys?

I want to derive $n$ keys from a master key. I pick a master key $mk$ and use pseudo-random function (PRF) to generate $n$ pseudo-random values, $v_i=PRF(mk,i)$ where $1\leq i \leq n$. Next, I use ...