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| 4 | <title>Finding 07: Missing Signature Verification in Offline ECDSA | Zion Boggan</title> |
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| 199 | <div class="kicker">Crypto soundness</div> |
| 200 | <h1>Finding 07: Missing Signature Verification in Offline ECDSA</h1> |
| 201 | </div></header> |
| 202 | <section><div class="wrap"><div class="content"> |
| 203 | <h2>Severity: P3 (Medium), Invalid signatures returned silently</h2> |
| 204 | <h2>Summary</h2> |
| 205 | <p>The offline ECDSA signing path combines partial signatures but does NOT verify the final result. A malicious cosigner can submit a corrupted partial <code>s_i</code> producing an invalid combined signature returned without error. The online path explicitly calls <code>GFp_curve_algebra_verify_signature()</code> before returning.</p> |
| 206 | <h2>Location</h2> |
| 207 | <ul> |
| 208 | <li><strong>File:</strong> <code>src/common/cosigner/cmp_ecdsa_offline_signing_service.cpp</code>, lines 425-447</li> |
| 209 | <li><strong>Missing:</strong> Final signature verification (present in online path at <code>cmp_ecdsa_online_signing_service.cpp:483</code>)</li> |
| 210 | </ul> |
| 211 | <h2>Remediation</h2> |
| 212 | <p>Add <code>algebra->verify()</code> call after signature combination in the offline path.</p> |
| 213 | <hr><p style="color:var(--faint);font-size:12.5px;font-family:ui-monospace,Menlo,monospace">Source · github.com/zionboggan/security-research-notebook · writeups/fireblocks/07-offline-ecdsa-no-sig-verify-P3.md</p> |
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| 217 | <div class="note">Coordinated-disclosure research. Findings appear here only after the program's disclosure window closed, the patch shipped, or a CVE was published. No customer data was accessed.</div> |
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