Accelerate eth_evm_modexp by 25x by dividing input size by 8 #249
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Found by @guidovranken in the Ethereum Foundation sponsored fuzzing campaign,
eth_evm_modexp is very slow on some input.
The issue is located here:
constantine/constantine/ethereum_evm_precompiles.nim
Lines 425 to 428 in d0f4ad8
constantine/constantine/ethereum_evm_precompiles.nim
Lines 455 to 457 in d0f4ad8
The issue is that multiplication scales quadratically, about 1.5n² with the number of words. In our case the ratio before/after is 25x leading to a DOS vulnerability