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Diffstat (limited to 'docs/units-and-global-variables.rst')
| -rw-r--r-- | docs/units-and-global-variables.rst | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/docs/units-and-global-variables.rst b/docs/units-and-global-variables.rst index 64795306..887535da 100644 --- a/docs/units-and-global-variables.rst +++ b/docs/units-and-global-variables.rst @@ -73,6 +73,18 @@ Block and Transaction Properties This includes calls to library functions. .. note:: + Do not rely on ``block.timestamp``, ``now`` and ``block.blockhash`` as a source of randomness, + unless you know what you are doing. + + Both the timestamp and the block hash can be influenced by miners to some degree. + Bad actors in the mining community can for example run a casino payout function on a chosen hash + and just retry a different hash if they did not receive any money. + + The current block timestamp must be strictly larger than the timestamp of the last block, + but the only guarantee is that it will be somewhere between the timestamps of two + consecutive blocks in the canonical chain. + +.. note:: If you want to implement access restrictions in library functions using ``msg.sender``, you have to manually supply the value of ``msg.sender`` as an argument. |