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add util to normalize s values #15

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Apr 4, 2024
Merged

add util to normalize s values #15

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6 changes: 3 additions & 3 deletions .gas-snapshot
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
WebAuthnFuzzTest:test_Verify_ShoulReturnFalse_WhenSAboveP256_N_DIV_2() (gas: 429635068)
WebAuthnFuzzTest:test_Verify_ShoulReturnFalse_WhenTheUpFlagIsNotSet() (gas: 435226970)
WebAuthnFuzzTest:test_Verify_ShoulReturnFalse_WhenUserVerifictionIsRequiredButTestWasNotPerformed() (gas: 432526116)
WebAuthnFuzzTest:test_Verify_ShoulReturnTrue_WhenSBelowP256_N_DIV_2() (gas: 456215767)
WebAuthnFuzzTest:test_Verify_ShoulReturnFalse_WhenTheUpFlagIsNotSet() (gas: 435310864)
WebAuthnFuzzTest:test_Verify_ShoulReturnFalse_WhenUserVerifictionIsRequiredButTestWasNotPerformed() (gas: 432573571)
WebAuthnFuzzTest:test_Verify_ShoulReturnTrue_WhenSBelowP256_N_DIV_2() (gas: 456300088)
WebAuthnTest:test_chrome() (gas: 225627)
WebAuthnTest:test_safari() (gas: 221874)
13 changes: 13 additions & 0 deletions test/Utils.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
pragma solidity ^0.8.0;

import {Base64Url} from "FreshCryptoLib/utils/Base64Url.sol";
import {FCL_Elliptic_ZZ} from "FreshCryptoLib/FCL_elliptic.sol";

struct WebAuthnInfo {
bytes authenticatorData;
Expand All @@ -10,6 +11,8 @@ struct WebAuthnInfo {
}

library Utils {
uint256 constant P256_N_DIV_2 = FCL_Elliptic_ZZ.n / 2;

function getWebAuthnStruct(bytes32 challenge) public pure returns (WebAuthnInfo memory) {
string memory challengeb64url = Base64Url.encode(abi.encode(challenge));
string memory clientDataJSON = string(
Expand All @@ -28,4 +31,14 @@ library Utils {

return WebAuthnInfo(authenticatorData, clientDataJSON, messageHash);
}

/// @dev normalizes the s value from a p256r1 signature so that
/// it will pass malleability checks.
function normalizeS(uint256 s) public pure returns (uint256) {
if (s > P256_N_DIV_2) {
return FCL_Elliptic_ZZ.n - s;
}

return s;
}
}
20 changes: 5 additions & 15 deletions test/Webauthn.fuzz.t.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -2,19 +2,17 @@
pragma solidity ^0.8.0;

import {FCL_ecdsa} from "FreshCryptoLib/FCL_ecdsa.sol";
import {FCL_Elliptic_ZZ} from "FreshCryptoLib/FCL_elliptic.sol";

import {WebAuthn} from "../src/WebAuthn.sol";

import "forge-std/Test.sol";
import "./Utils.sol";

contract WebAuthnFuzzTest is Test {
using stdJson for string;

string constant testFile = "/test/fixtures/assertions_fixture.json";

uint256 private constant P256_N_DIV_2 = FCL_Elliptic_ZZ.n / 2;

/// @dev `WebAuthn.verify` should return `false` when `s` is above P256_N_DIV_2.
function test_Verify_ShoulReturnFalse_WhenSAboveP256_N_DIV_2() public {
string memory rootPath = vm.projectRoot();
Expand All @@ -35,7 +33,7 @@ contract WebAuthnFuzzTest is Test {
console.log("Veryfing", jsonCaseSelector);

// Only interested in s > P256_N_DIV_2 cases.
if (webAuthnAuth.s <= P256_N_DIV_2) {
if (webAuthnAuth.s <= Utils.P256_N_DIV_2) {
webAuthnAuth.s = FCL_ecdsa.n - webAuthnAuth.s;
}

Expand Down Expand Up @@ -67,10 +65,7 @@ contract WebAuthnFuzzTest is Test {

console.log("Veryfing", jsonCaseSelector);

// Only interested in s <= P256_N_DIV_2 case
if (webAuthnAuth.s > P256_N_DIV_2) {
webAuthnAuth.s = FCL_ecdsa.n - webAuthnAuth.s;
}
webAuthnAuth.s = Utils.normalizeS(webAuthnAuth.s);

// Unset the `up` flag.
webAuthnAuth.authenticatorData[32] = webAuthnAuth.authenticatorData[32] & bytes1(0xfe);
Expand Down Expand Up @@ -109,9 +104,7 @@ contract WebAuthnFuzzTest is Test {
continue;
}

if (webAuthnAuth.s > P256_N_DIV_2) {
webAuthnAuth.s = FCL_ecdsa.n - webAuthnAuth.s;
}
webAuthnAuth.s = Utils.normalizeS(webAuthnAuth.s);

bool res = WebAuthn.verify({
challenge: challenge,
Expand Down Expand Up @@ -149,10 +142,7 @@ contract WebAuthnFuzzTest is Test {

console.log("Veryfing", jsonCaseSelector);

// Only interested in s <= P256_N_DIV_2 cases
if (webAuthnAuth.s > P256_N_DIV_2) {
webAuthnAuth.s = FCL_ecdsa.n - webAuthnAuth.s;
}
webAuthnAuth.s = Utils.normalizeS(webAuthnAuth.s);

bool res = WebAuthn.verify({challenge: challenge, requireUV: uv, webAuthnAuth: webAuthnAuth, x: x, y: y});

Expand Down