====== EIP 1052: EXTCODEHASH opcode  ======
[[dido:public:ra:xapend:xapend.b_stds:defact:ethereum:start| Return to Ethereum ERCs ]]

: **Note**: The following is an excerpt from the official Ethereum site. It is provided here as a convenience and is not authoritative. Refer to the original document as the authoritative reference.

<table>
<caption>Data sheet for EXTCODEHASH opcode</caption>
| Title                      | EXTCODEHASH opcode |
| EIP                        | 1052 |
| Author                     | <WRAP>
  * Nick Johnson <arachnid@notdot.net>, 
  * Paweł Bylica <pawel@ethereum.org>
</WRAP> |
| Status                     | Final |
| Created                    | 1018-05-02  |
| Description                | [[https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1052.md]] |
| Specification              | [[https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1052.md#Specification]] |
| Category                   | Core |
</table>

===== Abstract =====

This EIP specifies a new opcode, which returns the keccak256 hash of a contract's code.

===== Motivation =====

Many contracts need to perform checks on a contract's bytecode, but do not necessarily need the bytecode itself. For instance, a contract may want to check if another contract's bytecode is one of a set of permitted implementations, or it may perform analyses on code and whitelist any contract with matching bytecode if the analysis passes.

Contracts can presently do this using the **''EXTCODECOPY (0x3c)''** opcode, but this is expensive, especially for large contracts, in cases where only the hash is required. As a result, we propose a new opcode, **''EXTCODEHASH''**, which returns the keccak256 hash of a contract's bytecode.

/**=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
/* To add a discussion page to this page, comment out the line that says 
  ~~DISCUSSION:off~~
*/
~~DISCUSSION:on|Outstanding Issues~~
~~DISCUSSION:off~~