aboutsummaryrefslogtreecommitdiffstats
path: root/docs/units-and-global-variables.rst
diff options
context:
space:
mode:
authorAlex Beregszaszi <alex@rtfs.hu>2017-08-30 06:34:53 +0800
committerAlex Beregszaszi <alex@rtfs.hu>2017-09-02 02:13:26 +0800
commitf3230a41cebe4778c5c831e2bfa4fb3b7e10f4cb (patch)
treeb61142582f68fd64f97e424086c982ef4aa664bc /docs/units-and-global-variables.rst
parent8e1aae2e1a5c47fe11b5e17e670fcbb09ebda365 (diff)
downloaddexon-solidity-f3230a41cebe4778c5c831e2bfa4fb3b7e10f4cb.tar.gz
dexon-solidity-f3230a41cebe4778c5c831e2bfa4fb3b7e10f4cb.tar.zst
dexon-solidity-f3230a41cebe4778c5c831e2bfa4fb3b7e10f4cb.zip
Document caveats about timestamp and blockhash
Diffstat (limited to 'docs/units-and-global-variables.rst')
-rw-r--r--docs/units-and-global-variables.rst12
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.