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AFAIK there are 3 hash functions to choose from in solidity (sha3, sha256, and ripemd). sha3 is native while the others use precompiled contracts.

Which one of these is cheapest (in terms of gas)?

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  • Your questions is slightly ambiguous. You could improve your question by specifying what you mean with "cheap". I assume you mean "which hashing algorithm has the lowest gas cost?" (Cheap can also mean in terms of computational power). Commented Apr 20, 2016 at 7:58
  • @JeffreyW. done Commented Apr 20, 2016 at 12:31

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keccak256 (new alias for sha3) is cheapest.

Source: Yellow Paper

Appendix G mentions the gas cost of sha3 is:

  • 30 gas + 6 gas for each word (rounded up) for input data to a SHA3 Keccak-256 operation.

Appendix E has the costs for the others.

sha256 (SHA2-256) costs:

  • 60 gas + 12 gas for each word (rounded up) for input data to a SHA2-256 operation.

ripemd is even more expensive:

  • 600 gas + 120 gas for each word (rounded up) for input data to a RIPEMD-160 operation.
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    It's worth noting that calls to the sha3 built-in function (as opposed to the assembly directive) currently appear to create a contract invocation in Solidity, which is much more expensive than it needs to be. Commented Apr 20, 2016 at 9:52
  • @NickJohnson Sounds like a good question to ask if it is invoking a contract. (I kept my answer to the Yellow Paper, since values in an empirical, implementation dependent answer could change over time.) Commented Apr 21, 2016 at 10:33
  • @NickJohnson how do we know how we're calling it? is it the difference between blah = sha3(blah blah) and assembly { blah = sha3(blahblahblah) } ? Commented Nov 28, 2016 at 10:19
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    Can someone confirm if this is still the case? Commented May 3, 2018 at 15:51
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    @TharinduMadushanka Do you mean ethereum.stackexchange.com/questions/550/… ? Commented Jul 30, 2021 at 0:07

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