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Update units-and-global-variables.rst

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chriseth 2019-04-18 12:30:56 +02:00 committed by GitHub
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@ -189,8 +189,9 @@ Mathematical and Cryptographic Functions
.. warning::
If you use ``ecrecover``, be aware that a valid signature can be turned into a different valid signature without
requiring knowledge of the corresponding private key. Since `EIP-2 <http://eips.ethereum.org/EIPS/eip-2#specification>`_,
all transaction signatures with an ``s`` value greater than ``secp256k1n/2`` are considered invalid.
requiring knowledge of the corresponding private key. In the Homestead hard fork, this issue was fixed
for _transaction_ signatures (see `EIP-2 <http://eips.ethereum.org/EIPS/eip-2#specification>`_), but
the ecrecover function remained unchanged.
This is usually not a problem unless you require signatures to be unique or
use them to identify items. OpenZeppelin have a `ECDSA helper library <https://docs.openzeppelin.org/docs/cryptography_ecdsa>`_ that you can use as a wrapper for ``ecrecover`` without this issue.