EIP-7823: Set upper bounds for MODEXP #4070
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| /** | ||
| * Compute base^exp mod modulus for *arbitrarily* large BigInts | ||
| */ | ||
| function modPow(base: bigint, exp: bigint, modulus: bigint): bigint { |
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Can't this be done directly with bigints?
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When exponentiation is done natively with bigints using the ** operator, the value that's being raised to a power is literally formed in memory (base×base×⋯×base), which for very large numbers is astronomically huge and will quickly blow up with Maximum BigInt size exceeded. This helper function uses the binary exponentiation algorithm, similar to the actual precompile implementation, in order to get around that.
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I've also updated to remove the new helper method and just export the expMod helper function used in the precomp itself.
| it(`MODEXP should reject and consume all gas for inputs over 8192 bits in length - case ${maxInputLen} bytes`, async () => { | ||
| const result = await MODEXP({ | ||
| data: input, | ||
| gasLimit: BigInt(0xffffffff), |
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I think there should be a sanity check to confirm that this gasLimit is enough to pay for the precompile, but that the precompile now rejects it due to the incode length limit
…-monorepo into implement-eip-7823
…-monorepo into implement-eip-7823
…to implement-eip-7823
…to implement-eip-7823
The issue was because I was using |
| @@ -51,3 +71,81 @@ describe('Precompiles: MODEXP', () => { | |||
| assert.strictEqual(result.executionGasUsed, gas) | |||
| }) | |||
| }) | |||
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| function enoughGas(opts: PrecompileInput): boolean { | |||
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Now the "utility methods" are exported to calculate the gas fee here, but I think it would be more clean to instead write a gas calculator method inside the precompile and export that to calculate the required gas.
| } | ||
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| // sanity check to make sure there is enough gas in order to isolate error to cases causing OOG due to size limit of inputs | ||
| while (!enoughGas(opts)) opts.gasLimit *= BigInt(256) |
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If we then have the "calculate gas" method, we can thus "just set" this as the gasLimit. Even if the gas limit is enough, then it will still run out-of-gas because of the inputs being too large.
This change implements EIP-7823, which is being considered for inclusion in Fusaka. With this EIP activated, the MODEXP precompile will reject any requests with any inputs of length greater than 1024 bytes, and will consume all gas in the process.