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Wycheproof provides test vectors for validating cryptographic implementations. Use when testing crypto code for known attacks and edge cases.
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📦 Ships with trailofbits-skills
</> SKILL.md
wycheproof.SKILL.md
---name: wycheproof
type: domain
description: >
Wycheproof provides test vectors for validating cryptographic implementations.
Use when testing crypto code for known attacks and edge cases.
---# Wycheproof
Wycheproof is an extensive collection of test vectors designed to verify the correctness of cryptographic implementations and test against known attacks. Originally developed by Google, it is now a community-managed project where contributors can add test vectors for specific cryptographic constructions.
## Background
### Key Concepts
| Concept | Description |
|---------|-------------|
| Test vector | Input/output pair for validating crypto implementation correctness |
| Test group | Collection of test vectors sharing attributes (key size, IV size, curve) |
| Result flag | Indicates if test should pass (valid), fail (invalid), or is acceptable |
| Edge case testing | Testing for known vulnerabilities and attack patterns |
### Why This Matters
Cryptographic implementations are notoriously difficult to get right. Even small bugs can:
- Expose private keys
- Allow signature forgery
- Enable message decryption
- Create consensus problems when different implementations accept/reject the same inputs
| ChaCha20-Poly1305 | Use `chacha20_poly1305_test.json` | Tests AEAD implementation |
## Testing Workflow
```
Phase 1: Setup Phase 2: Parse Test Vectors
┌─────────────────┐ ┌─────────────────┐
│ Add Wycheproof │ → │ Load JSON file │
│ as submodule │ │ Filter by params│
└─────────────────┘ └─────────────────┘
↓ ↓
Phase 4: CI Integration Phase 3: Write Harness
┌─────────────────┐ ┌─────────────────┐
│ Auto-update │ ← │ Test valid & │
│ test vectors │ │ invalid cases │
└─────────────────┘ └─────────────────┘
```
## Repository Structure
The Wycheproof repository is organized as follows:
```text
┣ 📜 README.md : Project overview
┣ 📂 doc : Documentation
┣ 📂 java : Java JCE interface testing harness
┣ 📂 javascript : JavaScript testing harness
┣ 📂 schemas : Test vector schemas
┣ 📂 testvectors : Test vectors
┗ 📂 testvectors_v1 : Updated test vectors (more detailed)
```
The essential folders are `testvectors` and `testvectors_v1`. While both contain similar files, `testvectors_v1` includes more detailed information and is recommended for new integrations.
## Supported Algorithms
Wycheproof provides test vectors for a wide range of cryptographic algorithms:
| Tag forgery | Accepting modified authentication tags | AES-GCM, ChaCha20-Poly1305 | Various implementations |
### Signature Malleability: Deep Dive
**Problem:** Implementations that don't validate signature encoding can accept multiple valid signatures for the same message.
**Example (EdDSA):** Appending or removing zeros from signature:
```text
Valid signature: ...6a5c51eb6f946b30d
Invalid signature: ...6a5c51eb6f946b30d0000 (should be rejected)
```
**How to detect:**
```python
# Add signature length check
if len(sig) != 128: # EdDSA signatures must be exactly 64 bytes (128 hex chars)
return False
```
**Impact:** Can lead to consensus problems when different implementations accept/reject the same signatures.
**Related Wycheproof tests:**
- EdDSA: tcId 37 - "removing 0 byte from signature"
- ECDSA: tcId 06 - "Legacy: ASN encoding of r misses leading 0"
## Case Study: Elliptic npm Package
This case study demonstrates how Wycheproof found three CVEs in the popular elliptic npm package (3000+ dependents, millions of weekly downloads).
### Overview
The [elliptic](https://www.npmjs.com/package/elliptic) library is an elliptic-curve cryptography library written in JavaScript, supporting ECDH, ECDSA, and EdDSA. Using Wycheproof test vectors on version 6.5.6 revealed multiple vulnerabilities:
The pycryptodome library integrates Wycheproof test vectors in their test suite, demonstrating best practices for Python crypto implementations.
### Community Resources
- [C2SP Community](https://c2sp.org/) - Cryptographic specifications and standards community maintaining Wycheproof
- Wycheproof issues tracker - Report bugs in test vectors or suggest new constructions
## Summary
Wycheproof is an essential tool for validating cryptographic implementations against known attack vectors and edge cases. By integrating Wycheproof test vectors into your testing workflow:
1. Catch subtle encoding and validation bugs
2. Prevent signature malleability issues
3. Ensure consistent behavior across implementations
4. Benefit from community-contributed test vectors
5. Protect against known cryptographic vulnerabilities
The investment in writing a reusable testing harness pays dividends through continuous validation as new test vectors are added to the Wycheproof repository.
