Pseudo-random generation functions

Contract / Module:

  • free.util-random

Dependencies:

  • free.util-lists

  • free.util-strings

  • free.util-math

  • free.util-chain-data

This module provides random generation functions.

The random integers Xn are generated according to the following formula:

  • Xn = HASH(Xn-1 + TxHash + HASH(block-time))

  • Xn is stored in database for the next iteration

The random strings is derived from Xn with the following formula:

S = HASH( [Xn + 1] ) + HASH ( [Xn + 2] ) + HASH ( [Xn + 3] ) + ……….

The result is easy to predict. Even if block-time includes microseconds, block-time is an exact copy of the creation-time of the previous block.

That’s why a contract whose security would rely on that module would be highly exploitable.

An attacker just need to watch the current block, to predict what will be the generated numbers in the next block.

DO NOT NOT NOT USE this PRBS generator for cryptographic or lottery purposes.

Several numbers can be generated in the same block or transaction. They will be all different, and uncorrelated.

Integers

random-int

→ integer Returns a 256 bit random integer

pact> (random-int)
42217767265191416845873285650063916717654783831511640486359396574333357048814

pact> (random-int)
111356071076120320443192908521083690658058559363319245130075594187850043340684

random-int-range

_min integer _max integer → integer

Returns a random integer in range [min - max].

pact> (random-int-range 0 10)
6

pact> (random-int-range 0 10)
7

pact> (random-int-range 0 10)
0

Booleans

random-bool

→ bool

Returns a random boolean

pact> (random-bool)
true

pact> (random-bool)
true

pact> (random-bool)
false

Decimals

random-decimal-range

_min decimal _max decimal → decimal

Returns a random decimal in range [min - max].

pact> (random-decimal-range  -1.0 1.0)
0.636958912683

pact> (random-decimal-range -1.0 1.0)
0.857566630911

pact> (random-decimal-range -1.0 1.0)
0.376521587006

Lists

random-choice

choices-list [<a>] → <a>

Returns a random element from the non-empty list.

pact> (random-choice ["Cat", "Dog", "Horse", "Rabbit"])
"Rabbit"

pact> (random-choice ["Cat", "Dog", "Horse", "Rabbit"])
"Cat"

pact> (random-choice ["Cat", "Dog", "Horse", "Rabbit"])
"Cat"

pact> (random-choice ["Cat", "Dog", "Horse", "Rabbit"])
"Dog"

shuffle

in [<a>] → [<a>]

Shuffles a list using a sort method with random indexes.

pact> (+ "My preference pets order list is:" (to-string (shuffle ["Cat", "Dog", "Horse", "Rabbit", "Snake", "Ferret", "Rat", "Goldfish"])))
"My preference pets order list is:["Dog" "Horse" "Rat" "Snake" "Ferret" "Rabbit" "Cat" "Goldfish"]"

pact> (+ "My preference pets order list is:" (to-string (shuffle ["Cat", "Dog", "Horse", "Rabbit", "Snake", "Ferret", "Rat", "Goldfish"])))
"My preference pets order list is:["Rat" "Snake" "Dog" "Cat" "Horse" "Ferret" "Rabbit" "Goldfish"]"

pact> (+ "My preference pets order list is:" (to-string (shuffle ["Cat", "Dog", "Horse", "Rabbit", "Snake", "Ferret", "Rat", "Goldfish"])))
"My preference pets order list is:["Ferret" "Goldfish" "Horse" "Cat" "Rat" "Dog" "Snake" "Rabbit"]"

pact> (+ "My preference pets order list is:" (to-string (shuffle ["Cat", "Dog", "Horse", "Rabbit", "Snake", "Ferret", "Rat", "Goldfish"])))
"My preference pets order list is:["Cat" "Rat" "Goldfish" "Rabbit" "Ferret" "Snake" "Dog" "Horse"]"

pact> (+ "My preference pets order list is:" (to-string (shuffle ["Cat", "Dog", "Horse", "Rabbit", "Snake", "Ferret", "Rat", "Goldfish"])))
"My preference pets order list is:["Goldfish" "Rat" "Snake" "Cat" "Ferret" "Horse" "Rabbit" "Dog"]"

Strings

random-string

len integer → string

Returns a random string of length len.

pact> (random-string 5)
"5KkYZ"

pact> (random-string 129)
"uNeV0pWbdBtGA6eIOZ34iLlE62QtkPrpwXurESXfjjEbls5ViT6Hs3wISs4WMMlEUS2hGl9tAd1vjy3HREdgdwed8pgJkBbPxj5Q7eiTkvoEgnE4cwFNWqM1qvjOFmNb0"

gen-uuid-rfc-4122-v4

→ string

Generate an UUID (Universal Unique ID) according to RFC 4122 v4.

pact> (gen-uuid-rfc-4122-v4)
"c69c765d-46bd-4673-973b-09f1498921b3"

pact> (gen-uuid-rfc-4122-v4)
"11cebf69-41ce-485d-85f0-644630f7b5c6"