Update randomness.md

Author: 0x3bfc

docs/randomness.md

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 Generate a random number of a predefined interval in the deterministic environment of a blockchain.
 
 ## Motivation
-Randomness in computer systems and especially in Ethereum is notoriously difficult to achieve. While it is hard or even impossible to generate a truly random number via software, the need for randomness in Ethereum is high. This stems from the fact that a high percentage of smart contracts on the Ethereum blockchain can be classified as games, which often rely on some kind of randomness to determine a winner. The problem with randomness in Ethereum is that Ethereum is a deterministic Touring machine, with no inherent randomness involved. A majority of miners have to obtain the same result when evaluating a transaction to reach consensus. Consensus is one of the pillars of blockchain technology and randomness would imply that mutual agreement between all nodes is impossible. Another problem is the public nature of a blockchain. The internal state of a contract, as well as the entire history of a blockchain, is visible to the public. Therefore, it is difficult to find a secure source of entropy. One of the first sources of randomness in Ethereum that came to mind were block timestamps. The problem with block timestamps is, that they can be influenced by the miner, as long as the timestamp is not older than its parent block. Most of the time the timestamps will be close to correct, but if a miner has an incentive to benefit from wrong timestamps, he could use his mining power, in order to mine his blocks with incorrect timestamps to manipulate the outcome of the random function to his favor.
+Randomness in computer systems and especially in Ethereum is notoriously difficult to achieve. While it is hard or even impossible to generate a truly random number via software, the need for randomness in Ethereum is high. This stems from the fact that a high percentage of smart contracts on the Ethereum blockchain can be classified as games, which often rely on some kind of randomness to determine a winner. The problem with randomness in Ethereum is that Ethereum is a deterministic Turing machine, with no inherent randomness involved. A majority of miners have to obtain the same result when evaluating a transaction to reach consensus. Consensus is one of the pillars of blockchain technology and randomness would imply that mutual agreement between all nodes is impossible. Another problem is the public nature of a blockchain. The internal state of a contract, as well as the entire history of a blockchain, is visible to the public. Therefore, it is difficult to find a secure source of entropy. One of the first sources of randomness in Ethereum that came to mind were block timestamps. The problem with block timestamps is, that they can be influenced by the miner, as long as the timestamp is not older than its parent block. Most of the time the timestamps will be close to correct, but if a miner has an incentive to benefit from wrong timestamps, he could use his mining power, in order to mine his blocks with incorrect timestamps to manipulate the outcome of the random function to his favor.
 
 Several workarounds have been developed that overcome this limitations in one way or the other. They can be differentiated into the following groups, each with their respective benefits and downsides:
 * **Block hash PRNG** - the hash of a block as source of randomness