CVE-2025-69287

# BRC-104 Authentication Signature Data Preparation Vulnerability ### Summary A critical cryptographic vulnerability in the TypeScript SDK's BRC-104 authentication implementation caused incorrect signature data preparation, resulting in signature incompatibility [between SDK implementations](https://github.com/F1r3Hydr4nt/brc104-cross-language-tests) and potential authentication bypass scenarios. ### Details The vulnerability was located in the `Peer.ts` file of the TypeScript SDK, specifically in the `processInitialRequest` and `processInitialResponse` methods where signature data is prepared for BRC-104 mutual authentication. **Vulnerable Code Locations:** - `ts-sdk/src/auth/Peer.ts` lines 527-531 (signing) - `ts-sdk/src/auth/Peer.ts` lines 584-590 (verification) **Root Cause:** The TypeScript SDK incorrectly prepared signature data by: 1. Concatenating base64-encoded nonce strings: `message.initialNonce + sessionNonce` 2. Then decoding the concatenated base64 string: `base64ToBytes(concatenatedString)` This produced ~32-34 bytes of signature data instead of the correct 64 bytes. **Buggy Implementation (Before Fix):** ```typescript // CRITICAL BUG: Concatenating base64 strings before decoding data: Peer.base64ToBytes(message.initialNonce + sessionNonce) ``` **Correct Implementation (After Fix):** The fix properly decodes each base64 nonce individually, then concatenates the byte arrays: ```typescript data: [ ...Peer.base64ToBytes(message.initialNonce), ...Peer.base64ToBytes(sessionNonce) ] ``` **Why This is Critical:** BRC-104 authentication relies on cryptographic signatures to establish mutual trust between peers. When signature data preparation is incorrect: - Signatures generated by the TypeScript SDK don't match those expected by Go/Python SDKs - Cross-implementation authentication fails - An attacker could potentially exploit this to bypass authentication checks ### PoC The cross-language test suite demonstrates this vulnerability: 1. **Setup**: Use identical nonces and cryptographic inputs across TypeScript, Python, and Go SDKs 2. **Vulnerable behavior**: TypeScript SDK produces different signature data than Go/Python reference implementations 3. **Impact demonstration**: Authentication attempts between TypeScript clients and Go/Python servers fail due to signature mismatch **Test Evidence:** ```typescript // Buggy approach (produces ~32-34 bytes) const concatenatedB64 = INITIAL_NONCE_B64 + SESSION_NONCE_B64; const buggyResult = Array.from(Buffer.from(concatenatedB64, 'base64')); // Correct approach (produces 64 bytes) const correctResult = [...INITIAL_NONCE_BYTES, ...SESSION_NONCE_BYTES]; ``` **Base64 Padding Short Circuit Analysis:** The vulnerability occurs because base64 padding characters (`=`) act as early termination signals for base64 decoders. When concatenating base64 strings before decoding: 1. **Individual nonces:** Each 44-character base64 string decodes to 32 bytes 2. **Concatenated string:** 88-character string containing padding in the middle 3. **Decoding result:** Base64 decoder stops at the first `=` padding character, producing only 32 bytes instead of 64 **Example with test data:** - `INITIAL_NONCE_B64`: `"QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUE="` (44 chars → 32 bytes) - `SESSION_NONCE_B64`: `"QkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkI="` (44 chars → 32 bytes) - **Concatenated:** `"QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUE=QkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkJCQkI="` - **Buggy decode:** Only 32 bytes (decoder stops at first `=`) - **Correct decode:** 64 bytes (32 + 32, decoded separately then concatenated) ### Impact **Vulnerability Type:** Cryptographic signature verification bypass **Severity:** Critical (CVSS 9.1 - Critical) **Affected Systems:** - TypeScript SDK clients attempting to authenticate with Go or Python SDK servers - Any BRC-104 implementation relying on cross-SDK compatibility - Mutual authentication protocols using the affected signature preparation **Who is Impacted:** - Applications using the TypeScript SDK for BRC-104 authentication - Systems requiring cross-language/SDK authentication compatibility - Any peer-to-peer authentication scenarios where TypeScript clients communicate with non-TypeScript servers **Potential Attack Vectors:** - Authentication bypass through signature verification failure - Man-in-the-middle attacks if authentication is silently ignored - Denial of service through failed authentication attempts The fix ensures all SDKs now produce identical cryptographic signatures, restoring proper mutual authentication across implementations.