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Use assembly in WebAuthnVerifier for Base64 encoding #318

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merged 12 commits into from
Mar 27, 2024
Merged

Use assembly in WebAuthnVerifier for Base64 encoding #318

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118428f
[#289] Use assembly in WebAuthnVerifier for Base64 encoding
akshay-ap Mar 11, 2024
f4c2e88
[#289] Store Base64 encoded value without allocating string variable
akshay-ap Mar 12, 2024
74ded1f
[#289] Update WebAuthnVerifier in passkey package
akshay-ap Mar 13, 2024
e3faff8
Update modules/4337/contracts/experimental/verifiers/WebAuthnVerifier…
akshay-ap Mar 13, 2024
70999e1
Update modules/passkey/contracts/verifiers/WebAuthnVerifier.sol
akshay-ap Mar 13, 2024
5ab7fac
Fix lint issue
akshay-ap Mar 13, 2024
5c94b47
Merge branch 'main' of github.com:safe-global/safe-modules into featu…
mmv08 Mar 25, 2024
43882d0
Remove vendored library
mmv08 Mar 25, 2024
a8928b7
Add optimized Base64URL implementation for bytes32
mmv08 Mar 25, 2024
1952444
Add codesize task
mmv08 Mar 26, 2024
063de78
Update modules/passkey/contracts/libraries/Base64Url.sol
mmv08 Mar 27, 2024
e526a35
Improve the comment on exiting the loop
mmv08 Mar 27, 2024
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60 changes: 58 additions & 2 deletions modules/4337/contracts/experimental/verifiers/WebAuthnVerifier.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@
pragma solidity >=0.8.0;
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The experimental code will be removed, so I wouldn't update it here as well.


import {P256Wrapper} from "./P256Wrapper.sol";
import {Base64Url} from "../../vendor/FCL/utils/Base64Url.sol";

/**
* @title WebAuthnConstants
Expand Down Expand Up @@ -90,6 +89,9 @@ interface IWebAuthnVerifier {
contract WebAuthnVerifier is IWebAuthnVerifier, P256Wrapper {
constructor(address verifier) P256Wrapper(verifier) {}

string internal constant ENCODING_TABLE =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

/**
* @dev Generates a signing message based on the authenticator data, challenge, and client data fields.
* @param authenticatorData Authenticator data.
Expand All @@ -102,7 +104,61 @@ contract WebAuthnVerifier is IWebAuthnVerifier, P256Wrapper {
bytes32 challenge,
bytes calldata clientDataFields
) internal pure returns (bytes32 message) {
string memory encodedChallenge = Base64Url.encode(abi.encodePacked(challenge));

// Result is 44 bytes long because the encoded challenge is 32 bytes long
// 4*(32 + 2)/3 = 44 after rounding.
string memory table = ENCODING_TABLE;
string memory encodedChallenge = new string(44);
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assembly {
// Skip first 32 bytes of the table containing the length
let tablePtr := add(table, 1)
// Skip first 32 bytes of the encodedChallenge containing the length
let resultPtr := add(encodedChallenge, 32)

// Temporarily stores 3 bytes of challenge
let buffer
for{let i:= 0} lt(i, 10)
{
i := add(i, 1)
}{
// Calculate the shift value to get the 3 bytes of challenge
let shift := sub(256, mul(add(i, 1), 24))
buffer := and(shr(shift, challenge), 0xFFFFFF)

mstore8(resultPtr, mload(add(tablePtr, and(shr(18, buffer), 0x3F))))
resultPtr := add(resultPtr, 1)

mstore8(resultPtr, mload(add(tablePtr, and(shr(12, buffer), 0x3F))))
resultPtr := add(resultPtr, 1)

mstore8(resultPtr, mload(add(tablePtr, and(shr(6, buffer), 0x3F))))
resultPtr := add(resultPtr, 1)

mstore8(resultPtr, mload(add(tablePtr, and(buffer, 0x3F))))
resultPtr := add(resultPtr, 1)
}

// As 32 bytes input is not divisible by 3, process last 2 bytes of challenge separately
buffer := shl(8, and(challenge, 0xFFFF))

mstore8(resultPtr, mload(add(tablePtr, and(shr(18, buffer), 0x3F))))
resultPtr := add(resultPtr, 1)

mstore8(resultPtr, mload(add(tablePtr, and(shr(12, buffer), 0x3F))))
resultPtr := add(resultPtr, 1)

mstore8(resultPtr, mload(add(tablePtr, and(shr(6, buffer), 0x3F))))
resultPtr := add(resultPtr, 1)

mstore8(resultPtr, mload(add(tablePtr, and(buffer, 0x3F))))
resultPtr := add(resultPtr, 1)

// Because the input is fixed 32 bytes long
resultPtr := sub(resultPtr, 1)
mstore(encodedChallenge, sub(resultPtr, add(encodedChallenge, 32)))
}

/* solhint-disable quotes */
bytes memory clientDataJson = abi.encodePacked(
'{"type":"webauthn.get","challenge":"',
Expand Down
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