crypto(experiment): Add modexp abstraction plus GMP implementation (based off of #32174) #32187
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Co-authored-by: Felix Lange <[email protected]>
| - **macOS**: `brew install gmp` | ||
| - **Windows**: See [GMP Windows builds](https://gmplib.org/) | ||
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| > TODO: There is an alternative branch, where we compile from source however this is slightly messier (though it allows us to pin to a specific commit like we do for libsecp256k1) |
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The other way to install gmp would be to download the gmp repo, compile it locally and then package the static lib. I have a repo that does it like that here for reference: https://github.com/kevaundray/go-gmp/tree/master?tab=readme-ov-file#building-from-source
Its not as nice as just apt install libgmp-dev and it requires someone to explicitly call a script to compile the gmp source code vs using apt/brew/dnf -- it does give more control over the GMP that gets included with geth though and the compile flags that are used
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| ## License | ||
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| TODO -- whatever go-ethereum does. |
| // Special case: zero modulus | ||
| allZero := true | ||
| for _, b := range mod { | ||
| if b != 0 { | ||
| allZero = false | ||
| break | ||
| } | ||
| } | ||
| if allZero { | ||
| return []byte{}, nil | ||
| } |
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Haven't checked how GMP handles modulus == 0 -- if it does, then can remove this if its faster for gmp to do it
crypto/modexp/gmp/gmp.go
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| // Keep the slices alive until after the C call completes | ||
| runtime.KeepAlive(base) | ||
| runtime.KeepAlive(exp) | ||
| runtime.KeepAlive(mod) | ||
| runtime.KeepAlive(result) |
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Common pattern to stop the slices being deallocated
| } | ||
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| // Perform modular exponentiation | ||
| mpz_powm(result_mpz, base_mpz, exp_mpz, mod_mpz); |
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Theres a powm_ui method for short exponents -- might want to benchmark to see if its worth it
| if (*result_len < needed) { | ||
| mpz_clears(base_mpz, exp_mpz, mod_mpz, result_mpz, NULL); | ||
| return -2; | ||
| } |
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This should never trigger since the golang code allocated enough bytes to hold the modulus
| import ( | ||
| "github.com/ethereum/go-ethereum/crypto/modexp/gmp" | ||
| ) | ||
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| // ModExp performs modular exponentiation on byte arrays | ||
| // result = base^exp mod mod | ||
| // This uses the gmp implementation by default. | ||
| // To use bigint implementation, import crypto/modexp/bigint directly. | ||
| func ModExp(base, exp, mod []byte) ([]byte, error) { | ||
| return gmp.ModExp(base, exp, mod) | ||
| } |
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Similar API to bn254, can switch to big.Int by changing the import
This PR is based off of #32184 so the diff is larger than it seems and supersedes #32174
There are some optimizations that have not been transferred over from #32174 -- these are likely fine, since we mainly want to see the diff with gmp.