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feat(cheatcodes): Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto) #11267

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feat(cheatcodes): Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto) #11267

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@Ectario Ectario commented Aug 10, 2025 •
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Motivation

Security researchers and advanced test writers sometimes need to create deterministic ECDSA signatures with a chosen ephemeral nonce k.

This is useful to:

  • Reproduce signatures deterministically for debugging or reproducibility.
  • Stress test and fuzz systems that rely on signature uniqueness.

Currently, Foundry's vm.sign only derives k internally (RFC6979) and does not allow injecting a fixed nonce.
For security testing and deeper protocol analysis, we need a way to supply k manually.

Closes #11266.

Solution

This PR introduces a new cheatcode:

function signWithNonce(uint256 privateKey, bytes32 digest, uint256 nonce)
    external
    returns (uint8 v, bytes32 r, bytes32 s);
  • Signs digest on secp256k1 using privateKey and a user-supplied nonce k.
  • Requires both privateKey and nonce to be in (0, n) where n is the secp256k1 curve order.
  • Performs low-s normalization and recovery id computation.
  • Intended primarily for security testing, fuzzing, and reproducing edge cases — not for production signing.

Changes include:

  • crypto.rs implementation of the fixed-nonce signing path.
  • Integration in the cheatcodes Vm.sol interface.
  • New Solidity tests in testdata/default/cheats/Sign.t.sol covering valid and invalid nonce cases.

PR Checklist

  • Added Tests
  • Added Documentation

Question

EDIT: Just wondering, was it intentional to not have cargo cheats included in the make pr target in the Makefile? (And is it expected that the first cargo cheats crashes but the second runs fine?)

@Ectario Ectario requested a review from DaniPopes as a code owner August 10, 2025 15:38
@Ectario Ectario changed the title Gen sig with nonce feat: Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto) Aug 10, 2025
@Ectario Ectario changed the title feat: Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto) feat(cheatcodes): Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto) Aug 12, 2025
@Ectario Ectario changed the title feat(cheatcodes): Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto) feat(cheatcodes): Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto) Aug 12, 2025
onbjerg
onbjerg reviewed Aug 21, 2025
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some nits (not a final review)

Ectario and others added 2 commits August 21, 2025 17:06
@Ectario @onbjerg
Update crates/cheatcodes/spec/src/vm.rs
269d851 
review modification

Co-authored-by: onbjerg <[email protected]>
@Ectario @onbjerg
Update crates/cheatcodes/src/crypto.rs
1b24256 
review modification (better format)

Co-authored-by: onbjerg <[email protected]>
@0xrusowsky
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given the security concerns, and the fact that this is only useful for security researchers, imo we should rename the cheatcode to include the unsafe word (or any other visual warning that discourages SC devs from using it without a very good reason).

i'd either do unsafeSignWithNonce or signWithNonceUnsafe

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Ectario commented Aug 21, 2025

given the security concerns, and the fact that this is only useful for security researchers, imo we should rename the cheatcode to include the unsafe word (or any other visual warning that discourages SC devs from using it without a very good reason).

i'd either do unsafeSignWithNonce or signWithNonceUnsafe

That's a good idea.
(I think the second option signWithNonceUnsafe is better, since IDEs will suggest it when just typing vm.sign)

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feat(cheatcode): Add vm.signWithNonce(privateKey, digest, nonce) cheatcode (Crypto)
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