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Posted to commits@tooling.apache.org by as...@apache.org on 2026/04/22 00:02:37 UTC
(tooling-agents) branch main updated: ASVS L3 audit: 11.1.2 (vote_encryption_and_crypto)
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new b8b1420 ASVS L3 audit: 11.1.2 (vote_encryption_and_crypto)
b8b1420 is described below
commit b8b1420ee03f07e09111a68ce96b6262a4e2b3c7
Author: ASF Tooling Team <ro...@apache.org>
AuthorDate: Wed Apr 22 02:02:32 2026 +0200
ASVS L3 audit: 11.1.2 (vote_encryption_and_crypto)
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+# ASVS 11.1.2 Audit Report: Apache STeVe Voting System
+
+## Executive Summary
+
+- **Repository:** apache/steve
+- **Audit Date:** Apr 21, 2026
+- **Auditor:** Tooling Agents
+- **ASVS Requirement:** 11.1.2 — Verify that a cryptographic inventory is performed, maintained, regularly updated, and includes all cryptographic keys, algorithms, and certificates used by the application. It must also document where keys can and cannot be used in the system, and the types of data that can and cannot be protected using the keys.
+- **ASVS Level:** 2
+- **Section:** Cryptographic Inventory and Documentation
+- **Files Analyzed:** 4 relevant out of 4 total, 0 skipped
+
+### Finding Summary
+
+| Severity | Count | Finding IDs |
+|----------|-------|-------------|
+| Critical | 0 | - |
+| High | 1 | ASVS-1112-HIGH-001 |
+| Medium | 3 | ASVS-1112-MED-002, ASVS-1112-MED-003, ASVS-1112-MED-004 |
+| Low | 0 | - |
+| **Total** | **4** | |
+
+### Key Findings
+
+The application implements a sophisticated multi-layered cryptographic architecture for vote encryption and election integrity, but **lacks a formal cryptographic inventory document** as mandated by ASVS 11.1.2. Analysis reveals several concrete discrepancies between documented intent and actual implementation that would be identified and remediated through a proper inventory process, including algorithm variant mismatches and misleading documentation labels.
+
+---
+
+## Security Controls Inventory
+
+### Cryptographic Assets Discovered in Code
+
+| Asset | Algorithm/Primitive | Parameters | Location | Purpose |
+|-------|---------------------|------------|----------|---------|
+| Election Salt | CSPRNG (secrets) | 16 bytes | `crypto.py:34`, `schema.sql:81` | Seeding opened_key derivation |
+| Per-Voter Salt | CSPRNG (secrets) | 16 bytes | `crypto.py:34`, `schema.sql:170` | Per-voter key derivation |
+| Opened Key | BLAKE2b → Argon2**d** | 64B→32B, t=2, m=64MB, p=4 | `crypto.py:38-49` | Election integrity check |
+| Vote Token | Argon2**d** | t=2, m=64MB, p=4, len=32 | `crypto.py:52-56` | Per-voter vote identification |
+| Vote Encryption Key | HKDF-SHA256 | 32 bytes, info=`xchacha20_key` | `crypto.py:59-69` | Deriving Fernet key |
+| Vote Ciphertext | Fernet (AES-128-CBC + HMAC-SHA256) | 128-bit AES | `crypto.py:72-85` | Encrypting/decrypting votes |
+| Election IDs | CSPRNG (secrets) | 5 bytes (10 hex chars) | `crypto.py:117-121` | Unpredictable identifiers |
+| Shuffle | Fisher-Yates + secrets.randbelow | N/A | `crypto.py:101-114` | Vote anonymization |
+| Benchmark (testing) | Argon2**id** | variable | `crypto.py:124-156` | Parameter tuning |
+
+### Coverage Analysis
+
+| Component | Formal Inventory Document | Inline Documentation | Algorithm Consistency |
+|-----------|---------------------------|----------------------|------------------------|
+| Salt generation | ❌ No document | ✅ Comments present | ✅ Consistent |
+| Key derivation (Argon2) | ❌ No document | ⚠️ Partial | ❌ Type.D vs Type.ID mismatch |
+| Key stretching (HKDF) | ❌ No document | ❌ Misleading labels | ❌ XChaCha20 label, Fernet use |
+| Vote encryption (Fernet) | ❌ No document | ⚠️ Minimal | ✅ Consistent usage |
+| Tamper detection | ❌ No document | ⚠️ Partial | ⚠️ Non-constant-time compare |
+| Key lifecycle & boundaries | ❌ No document | ❌ Not documented | N/A |
+
+---
+
+## Critical File Review
+
+### `v3/steve/crypto.py` — Cryptographic Core
+
+| Line(s) | Function | Crypto Operation | Documented | Inventoried | Issue |
+|---------|----------|------------------|------------|-------------|-------|
+| 34-35 | `gen_salt()` | CSPRNG salt | ✅ | ❌ | No inventory |
+| 38-49 | `gen_opened_key()` | BLAKE2b → Argon2d | ✅ | ❌ | Argon2d not recommended |
+| 52-56 | `gen_vote_token()` | Argon2d | ✅ | ❌ | Argon2d not recommended |
+| 59-69 | `_b64_vote_key()` | HKDF-SHA256 | ⚠️ Wrong | ❌ | Label says XChaCha20 |
+| 72-77 | `create_vote()` | Fernet encrypt | ✅ | ❌ | No inventory |
+| 80-85 | `decrypt_votestring()` | Fernet decrypt | ✅ | ❌ | No inventory |
+| 88-98 | `_hash()` | Argon2d | ✅ | ❌ | Type.D vs benchmark Type.ID |
+| 101-114 | `shuffle()` | CSPRNG shuffle | ✅ | ❌ | No inventory |
+| 117-121 | `create_id()` | CSPRNG hex | ✅ | ❌ | No inventory |
+
+### `v3/steve/election.py` — Crypto Consumer
+
+| Line(s) | Function | Crypto Usage | State Check | Inventoried |
+|---------|----------|--------------|-------------|-------------|
+| 73 | `open()` | gen_salt, gen_opened_key | ✅ Editable | ❌ |
+| 130 | `add_salts()` | gen_salt per voter | ✅ Editable | ❌ |
+| 259-261 | `add_vote()` | gen_vote_token, create_vote | ✅ Open | ❌ |
+| 301-323 | `tally_issue()` | gen_vote_token, decrypt_votestring | ✅ Closed | ❌ |
+| 362-375 | `is_tampered()` | gen_opened_key | ⚠️ Any state | ❌ Non-constant-time |
+
+### `v3/schema.sql` — Crypto Storage
+
+| Table.Column | Type | Constraint | Purpose | Inventoried |
+|--------------|------|------------|---------|-------------|
+| election.salt | BLOB | len=16 | Election key derivation | ❌ |
+| election.opened_key | BLOB | len=32 | Tamper detection | ❌ |
+| mayvote.salt | BLOB | len=16 | Per-voter key derivation | ❌ |
+| vote.vote_token | BLOB | len=32 | Vote identification | ❌ |
+| vote.ciphertext | BLOB | NOT NULL | Encrypted vote | ❌ |
+
+---
+
+## Findings
+
+### High Severity
+
+#### ASVS-1112-HIGH-001: Absence of Formal Cryptographic Inventory Document
+
+**Severity:** HIGH
+**Gap Type:** Type A — No control exists
+**ASVS Requirement:** 11.1.2 (Level 2)
+
+**Location:**
+- **Files Affected:** `v3/steve/crypto.py` (entire file), `v3/steve/election.py` (entire file), `v3/schema.sql` (entire file)
+- **Functions:** All cryptographic functions across the codebase
+- **Lines:** N/A (systemic documentation gap)
+
+**Related Functions Checked:**
+- `crypto.gen_salt()` (line 34)
+- `crypto.gen_opened_key()` (lines 38-49)
+- `crypto.gen_vote_token()` (lines 52-56)
+- `crypto._b64_vote_key()` (lines 59-69)
+- `crypto.create_vote()` (lines 72-77)
+- `crypto.decrypt_votestring()` (lines 80-85)
+- `election.open()` (line 73)
+- `election.add_salts()` (line 130)
+- `election.is_tampered()` (lines 362-375)
+
+**Description:**
+
+ASVS 11.1.2 requires a cryptographic inventory that is "performed, maintained, regularly updated, and includes all cryptographic keys, algorithms, and certificates used by the application." No such document exists in the codebase. Cryptographic usage is spread across `crypto.py`, `election.py`, and `schema.sql` with inline comments that serve as the only documentation—and these are demonstrably inconsistent (see subsequent findings).
+
+**Evidence — Missing Documentation Areas:**
+
+1. **No algorithm registry:** Algorithms are discoverable only by reading source code. No centralized list of approved algorithms, their parameters, or their intended use.
+
+2. **No key boundary documentation (where keys can/cannot be used):**
+ - `opened_key` is used in `gen_vote_token()` and `is_tampered()` — not documented
+ - Per-voter `salt` is used for both vote_token derivation AND vote encryption key derivation — not documented
+ - No documentation that election salts must NOT be used for vote encryption
+
+3. **No data protection mapping (what data can/cannot be protected):**
+ - Vote strings are encrypted — not formally specified
+ - Election metadata (titles, descriptions) is NOT encrypted — no justification documented
+ - Voter eligibility data is NOT encrypted — acknowledged in domain context but not in code documentation
+
+4. **No key lifecycle documentation:**
+ - Salt generation occurs at election open (`election.py:119-138`) — lifecycle not documented
+ - `opened_key` is never rotated — policy not documented
+ - Key destruction after tallying — no policy exists
+
+**Vulnerable Code:**
+
+N/A — This is a documentation gap, not a code vulnerability. However, the absence of inventory has allowed inconsistencies to persist (see findings 002 and 003).
+
+**Data Flow:**
+
+```
+Election Creation → Salt Generation → Key Derivation → Vote Encryption
+ ↓ ↓ ↓ ↓
+ No docs No lifecycle docs No boundary docs No algorithm docs
+```
+
+**Proof of Concept:**
+
+Attempt to answer ASVS 11.1.2 requirements from existing documentation:
+
+```bash
+# Question: What cryptographic algorithms are used?
+$ grep -r "algorithm" v3/ --include="*.md" --include="*.txt"
+# Result: No formal documentation found
+
+# Question: Where can the opened_key be used?
+$ grep -r "opened_key" v3/ --include="*.md" --include="*.txt"
+# Result: No formal documentation found
+
+# Question: What is the key rotation policy?
+$ grep -r "rotation\|lifecycle" v3/ --include="*.md" --include="*.txt"
+# Result: No formal documentation found
+```
+
+**Impact:**
+
+Without a formal inventory, cryptographic drift goes undetected (as evidenced by findings 002 and 003 below). Algorithm transitions cannot be planned safely. Security audits require complete code review rather than document verification. Compliance with regulatory frameworks requiring crypto inventories (e.g., PCI DSS, NIST SP 800-57) cannot be demonstrated.
+
+**Remediation:**
+
+Create and maintain a `CRYPTO_INVENTORY.md` document at the project root:
+
+```markdown
+# Cryptographic Inventory — STeVe Voting System
+# Last Updated: YYYY-MM-DD
+# Review Frequency: Quarterly
+
+## 1. Algorithms
+
+| ID | Algorithm | Variant | Parameters | Approved | Used In | Purpose |
+|----|-----------|---------|------------|----------|---------|---------|
+| A1 | Argon2 | **id** | t=2,m=64MB,p=4,len=32 | Yes | crypto._hash() | Key derivation |
+| A2 | BLAKE2b | default | digest=64B | Yes | crypto.gen_opened_key() | Pre-hashing |
+| A3 | HKDF | SHA-256 | len=32,info=b'fernet_vote_key' | Yes | crypto._b64_vote_key() | Key stretching |
+| A4 | Fernet | AES-128-CBC+HMAC-SHA256 | 128-bit | Yes* | crypto.create_vote() | Vote encryption |
+
+*Note: AES-128 is minimum acceptable. Migration to XChaCha20-Poly1305 planned for vX.Y.
+
+## 2. Keys and Their Boundaries
+
+| Key | Derivation | Can Protect | Cannot Protect | Storage |
+|-----|-----------|-------------|----------------|---------|
+| Election Salt | secrets.token_bytes(16) | opened_key derivation only | Vote data | election.salt column |
+| Opened Key | BLAKE2b→Argon2id(edata, salt) | Vote token derivation, tamper detection | Direct vote encryption | election.opened_key column |
+| Per-Voter Salt | secrets.token_bytes(16) | vote_token + vote_key derivation | Other voter's votes | mayvote.salt column |
+| Vote Token | Argon2id(opened_key+pid+iid, salt) | Vote identification, encryption key derivation | Other issues' votes | vote.vote_token column |
+| Vote Key | HKDF(vote_token, salt) | Single voter's vote ciphertext | Aggregate data | Memory only (never stored) |
+
+## 3. Key Lifecycle
+[Document generation, storage, access, rotation, destruction policies]
+
+## 4. PQC Migration Plan
+[Document timeline for post-quantum algorithm adoption]
+```
+
+**Additional Actions:**
+1. Establish quarterly inventory review process with documented sign-off
+2. Integrate inventory verification into CI/CD pipeline
+3. Create automated tooling to detect cryptographic API usage not documented in inventory
+4. Document integration with external key management systems (config.yaml, asfquart secrets)
+
+---
+
+### Medium Severity
+
+#### ASVS-1112-MED-002: Undocumented Algorithm Variant Mismatch — Argon2d in Production vs Argon2id in Benchmark
+
+**Severity:** MEDIUM
+**Gap Type:** Type B — Control exists (benchmark uses Argon2id) but NOT applied (production uses Argon2d)
+**ASVS Requirement:** 11.1.2 (Level 2)
+
+**Location:**
+- **File:** `v3/steve/crypto.py`
+- **Functions:** `_hash()` (lines 88-98) vs `benchmark_argon2()` (lines 124-156)
+- **Line:** 97 (production), 150 (benchmark)
+
+**Related Functions Checked:**
+- `gen_opened_key()` (lines 38-49) — calls `_hash()` with Argon2d
+- `gen_vote_token()` (lines 52-56) — calls `_hash()` with Argon2d
+- `benchmark_argon2()` (lines 124-156) — tests Argon2id parameters
+
+**Description:**
+
+The production code uses Argon2d (`Type.D`) while the benchmark function tests Argon2id (`Type.ID`). This creates a discrepancy where:
+1. Performance and security testing is conducted on a different algorithm variant than production uses
+2. The recommended variant (Argon2id per RFC 9106 and OWASP guidance) is tested but not deployed
+3. A cryptographic inventory would have caught this inconsistency by requiring explicit documentation of algorithm variants
+
+**Vulnerable Code:**
+
+Production implementation in `_hash()` (line 97):
+```python
+def _hash(data: bytes, salt: bytes) -> bytes:
+ "Use Argon2id to hash the data, with default tuning parameters."
+ return argon2.low_level.hash_secret_raw(
+ secret=data,
+ salt=salt,
+ time_cost=2,
+ memory_cost=65536,
+ parallelism=4,
+ hash_len=32,
+ type=argon2.low_level.Type.D, # ← Argon2d - side-channel vulnerable
+ )
+```
+
+Benchmark implementation (line 150):
+```python
+def benchmark_argon2():
+ # ... setup code ...
+ hash_value = argon2.low_level.hash_secret_raw(
+ secret=secret,
+ salt=salt,
+ time_cost=time_cost,
+ memory_cost=memory_cost,
+ parallelism=parallelism,
+ hash_len=32,
+ type=argon2.low_level.Type.ID, # ← Argon2id - recommended variant
+ )
+```
+
+**Data Flow:**
+
+```
+Election Data → gen_opened_key() → _hash(Type.D) → opened_key (32 bytes)
+ ↓
+ Side-channel vulnerable
+
+Voter + Issue → gen_vote_token() → _hash(Type.D) → vote_token (32 bytes)
+ ↓
+ Side-channel vulnerable
+
+Benchmark Test → benchmark_argon2() → Type.ID → Performance metrics
+ ↓
+ NOT testing production code path
+```
+
+**Proof of Concept:**
+
+Demonstrating the algorithm mismatch:
+
+```python
+import argon2.low_level
+
+# Production configuration
+prod_hash = argon2.low_level.hash_secret_raw(
+ secret=b"test_data",
+ salt=b"0123456789abcdef",
+ time_cost=2,
+ memory_cost=65536,
+ parallelism=4,
+ hash_len=32,
+ type=argon2.low_level.Type.D, # Production
+)
+
+# Benchmark configuration
+bench_hash = argon2.low_level.hash_secret_raw(
+ secret=b"test_data",
+ salt=b"0123456789abcdef",
+ time_cost=2,
+ memory_cost=65536,
+ parallelism=4,
+ hash_len=32,
+ type=argon2.low_level.Type.ID, # Benchmark
+)
+
+print(f"Production: {prod_hash.hex()}")
+print(f"Benchmark: {bench_hash.hex()}")
+print(f"Match: {prod_hash == bench_hash}") # False - different algorithms
+```
+
+**Impact:**
+
+1. **Side-Channel Vulnerability:** Argon2d is vulnerable to cache-timing side-channel attacks, which could allow a co-located attacker (e.g., in cloud environments) to extract key material during key derivation. While exploitation requires precise timing measurement and repeated attempts, this is a known weakness of the Argon2d variant.
+
+2. **False Security Confidence:** The benchmark function testing Argon2id parameters gives false confidence that the recommended variant is in use, when production actually uses the less secure variant.
+
+3. **Inventory Gap:** A cryptographic inventory would have caught this discrepancy by requiring documentation of the specific algorithm variant in use, along with justification for choosing Argon2d over Argon2id.
+
+**Remediation:**
+
+Change production code to use Argon2id:
+
+```python
+# In crypto.py, _hash() function, line 97:
+def _hash(data: bytes, salt: bytes) -> bytes:
+ "Use Argon2id to hash the data, with default tuning parameters."
+ return argon2.low_level.hash_secret_raw(
+ secret=data,
+ salt=salt,
+ time_cost=2,
+ memory_cost=65536,
+ parallelism=4,
+ hash_len=32,
+ type=argon2.low_level.Type.ID, # Changed from Type.D to Type.ID
+ )
+```
+
+**Migration Plan:**
+
+> **CRITICAL:** This change will invalidate all existing `opened_key` values and `vote_token` values. A migration plan is required for any elections that have been opened:
+
+1. **For new elections:** Will automatically use Argon2id after code deployment
+2. **For open elections:** Must complete tallying before upgrade, or implement dual-algorithm support
+3. **For closed elections:** Historical data remains valid; tamper detection will need recalculation if verification is required
+
+This is precisely the kind of change that a cryptographic inventory with versioning would manage systematically.
+
+---
+
+#### ASVS-1112-MED-003: HKDF Domain Separation Label Mismatched with Actual Encryption Algorithm
+
+**Severity:** MEDIUM
+**Gap Type:** Type B — Domain separation exists but labels wrong algorithm, creating false inventory record
+**ASVS Requirement:** 11.1.2 (Level 2)
+
+**Location:**
+- **File:** `v3/steve/crypto.py`
+- **Function:** `_b64_vote_key()`
+- **Lines:** 59-69
+
+**Related Functions Checked:**
+- `create_vote()` (lines 72-77) — uses Fernet with keys from `_b64_vote_key()`
+- `decrypt_votestring()` (lines 80-85) — uses Fernet with keys from `_b64_vote_key()`
+- `gen_vote_token()` (lines 52-56) — provides input to `_b64_vote_key()`
+
+**Description:**
+
+The HKDF `info` parameter provides cryptographic domain separation per NIST SP 800-56C. The code uses `info=b'xchacha20_key'` while the actual encryption algorithm is Fernet (AES-128-CBC + HMAC-SHA256). This creates two problems:
+
+1. **Inventory Falsification:** Any automated or manual inventory reading the `info` field would incorrectly record XChaCha20-Poly1305 as the encryption algorithm.
+
+2. **Unsafe Algorithm Migration:** When the planned migration to XChaCha20-Poly1305 occurs (per the comment "will switch soon"), if the same `info=b'xchacha20_key'` is retained, the derived keys will be identical to the current Fernet keys. This eliminates cryptographic domain separation between the old and new algorithms.
+
+**Vulnerable Code:**
+
+```python
+def _b64_vote_key(vote_token: bytes, salt: bytes) -> bytes:
+ "Key-stretch the vote_token. (ref: PBKDF)"
+
+ ### still using Fernet now, but will switch soon. Leaving comments.
+ keymaker = hkdf.HKDF(
+ algorithm=hashes.SHA256(),
+ length=32, # 32-byte key for XChaCha20-Poly1305 ← COMMENT: Wrong algorithm
+ salt=salt,
+ info=b'xchacha20_key', # ← CRITICAL: Actual cipher is AES-128-CBC (Fernet)
+ )
+ vote_key = keymaker.derive(vote_token)
+ return base64.urlsafe_b64encode(vote_key)
+```
+
+Actual usage in `create_vote()` (line 75):
+```python
+def create_vote(vote_token: bytes, salt: bytes, votestring: str) -> bytes:
+ vote_key = _b64_vote_key(vote_token, salt)
+ f = Fernet(vote_key) # ← Using Fernet (AES-128-CBC), not XChaCha20
+ return f.encrypt(votestring.encode("utf-8"))
+```
+
+**Data Flow:**
+
+```
+vote_token (32 bytes)
+ ↓
+HKDF-SHA256(info=b'xchacha20_key') ← MISLEADING LABEL
+ ↓
+vote_key (32 bytes, base64-encoded)
+ ↓
+Fernet(vote_key) ← ACTUAL ALGORITHM: AES-128-CBC + HMAC-SHA256
+ ↓
+ciphertext
+```
+
+**Proof of Concept:**
+
+Demonstrating the mismatch between label and actual usage:
+
+```python
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.kdf.hkdf import HKDF
+from cryptography.fernet import Fernet
+import base64
+
+# Current implementation
+vote_token = b"0" * 32
+salt = b"1" * 16
+
+keymaker = hkdf.HKDF(
+ algorithm=hashes.SHA256(),
+ length=32,
+ salt=salt,
+ info=b'xchacha20_key', # Label says XChaCha20
+)
+vote_key = base64.urlsafe_b64encode(keymaker.derive(vote_token))
+
+# But actual usage is Fernet (AES-128-CBC)
+f = Fernet(vote_key)
+ciphertext = f.encrypt(b"test vote")
+
+# Inventory would record: "XChaCha20-Poly1305"
+# Actual algorithm: "AES-128-CBC + HMAC-SHA256"
+print(f"Label claims: XChaCha20-Poly1305")
+print(f"Actual algorithm: Fernet (AES-128-CBC + HMAC-SHA256)")
+```
+
+**Impact:**
+
+1. **Incorrect Inventory Records:** Any cryptographic inventory process that examines the code will record XChaCha20-Poly1305 as the vote encryption algorithm, when it is actually Fernet (AES-128-CBC + HMAC-SHA256).
+
+2. **Failed Domain Separation During Migration:** When migrating to XChaCha20-Poly1305, if the same `info` value is retained:
+ ```python
+ # Old system: HKDF(info=b'xchacha20_key') → Fernet
+ # New system: HKDF(info=b'xchacha20_key') → XChaCha20-Poly1305
+ # Result: Same keys for different algorithms - defeats domain separation
+ ```
+
+3. **Misleading Code Comments:** The comment "32-byte key for XChaCha20-Poly1305" is incorrect—Fernet uses 16 bytes for AES-128 and 16 bytes for HMAC signing key.
+
+**Remediation:**
+
+Correct the `info` parameter to match the actual algorithm:
+
+```python
+def _b64_vote_key(vote_token: bytes, salt: bytes) -> bytes:
+ "Key-stretch the vote_token into a Fernet-compatible key."
+ keymaker = hkdf.HKDF(
+ algorithm=hashes.SHA256(),
+ length=32, # 32 bytes: 16-byte signing key + 16-byte AES-128 key (Fernet spec)
+ salt=salt,
+ info=b'fernet_vote_key_v1', # Matches actual algorithm; version for migration
+ )
+ vote_key = keymaker.derive(vote_token)
+ return base64.urlsafe_b64encode(vote_key)
+```
+
+When migrating to XChaCha20-Poly1305, use a distinct `info` value:
+
+```python
+def _b64_vote_key_v2(vote_token: bytes, salt: bytes) -> bytes:
+ "Key-stretch the vote_token into an XChaCha20-Poly1305-compatible key."
+ keymaker = hkdf.HKDF(
+ algorithm=hashes.SHA256(),
+ length=32, # 32 bytes for XChaCha20-Poly1305
+ salt=salt,
+ info=b'xchacha20_vote_key_v2', # New domain for new algorithm
+ )
+ vote_key = keymaker.derive(vote_token)
+ return base64.urlsafe_b64encode(vote_key)
+```
+
+**Inventory Documentation Required:**
+
+```markdown
+## Algorithm Migration History
+
+| Version | Algorithm | HKDF Info Parameter | Key Length | Valid From | Valid Until |
+|---------|-----------|---------------------|------------|------------|-------------|
+| v1 | Fernet (AES-128-CBC + HMAC-SHA256) | `fernet_vote_key_v1` | 32 bytes | 2024-01 | Current |
+| v2 | XChaCha20-Poly1305 | `xchacha20_vote_key_v2` | 32 bytes | TBD | Future |
+```
+
+---
+
+#### ASVS-1112-MED-004: Non-Constant-Time Cryptographic Comparison in Tamper Detection
+
+**Severity:** MEDIUM
+**Gap Type:** Type C — Control exists (tamper check) but comparison result may leak information through timing
+**ASVS Requirement:** 11.1.2 (Level 2)
+
+**Location:**
+- **File:** `v3/steve/election.py`
+- **Function:** `is_tampered()`
+- **Line:** 375
+
+**Related Functions Checked:**
+- `gen_opened_key()` in `crypto.py` (lines 38-49) — generates the comparison value
+- `gather_election_data()` in `election.py` (line 368) — gathers data for integrity check
+- `tally()` in `tally.py` (lines 152-154) — calls `is_tampered()` before processing votes
+
+**Description:**
+
+The `is_tampered()` function uses Python's `!=` operator to compare cryptographic keys. This operator performs byte-by-byte comparison that short-circuits on the first differing byte, creating a timing side-channel. While both values being compared are Argon2 hashes (making practical exploitation difficult), cryptographic best practice mandates constant-time comparison for all secret material.
+
+A proper cryptographic inventory would document that all cryptographic comparisons must use constant-time functions to prevent timing side-channels.
+
+**Vulnerable Code:**
+
+```python
+def is_tampered(self, pdb):
+ md = self._all_metadata()
+ edata = self.gather_election_data(pdb)
+ opened_key = crypto.gen_opened_key(edata, md.salt)
+
+ # The computed key should be unchanged.
+ return opened_key != md.opened_key # ← Python != short-circuits on first differing byte
+```
+
+**Data Flow:**
+
+```
+Election Metadata → gather_election_data() → edata
+ ↓
+ gen_opened_key(edata, salt)
+ ↓
+ computed_opened_key (32 bytes)
+ ↓
+ Python != comparison ← stored_opened_key (32 bytes)
+ ↓
+ Returns on first byte mismatch
+ ↓
+ Timing reveals position of first difference
+```
+
+**Proof of Concept:**
+
+Demonstrating timing difference in non-constant-time comparison:
+
+```python
+import time
+import secrets
+
+# Simulate stored and computed keys
+stored_key = secrets.token_bytes(32)
+
+# Case 1: Keys differ in first byte
+computed_key_early = bytes([stored_key[0] ^ 0xFF]) + stored_key[1:]
+
+start = time.perf_counter_ns()
+for _ in range(100000):
+ result = stored_key != computed_key_early
+end = time.perf_counter_ns()
+time_early = end - start
+
+# Case 2: Keys differ in last byte
+computed_key_late = stored_key[:-1] + bytes([stored_key[-1] ^ 0xFF])
+
+start = time.perf_counter_ns()
+for _ in range(100000):
+ result = stored_key != computed_key_late
+end = time.perf_counter_ns()
+time_late = end - start
+
+print(f"Time for early mismatch: {time_early} ns")
+print(f"Time for late mismatch: {time_late} ns")
+print(f"Difference: {abs(time_late - time_early)} ns")
+# Typically shows measurable difference
+```
+
+**Impact:**
+
+1. **Timing Side-Channel:** An attacker with the ability to modify election data and observe response timing could theoretically deduce bytes of the stored `opened_key` through repeated attempts and precise timing measurement.
+
+2. **Limited Practical Exploitability:** Both values being compared are Argon2 hashes, which makes practical exploitation difficult. The attacker would need:
+ - Ability to modify election data
+ - Precise timing measurement capability
+ - Many repeated attempts
+ - Statistical analysis of timing variations
+
+3. **Cryptographic Best Practice Violation:** Regardless of practical exploitability, constant-time comparison is a fundamental cryptographic hygiene requirement. A proper inventory would have documented this requirement.
+
+**Remediation:**
+
+Use `hmac.compare_digest()` for constant-time comparison:
+
+```python
+import hmac
+
+def is_tampered(self, pdb):
+ md = self._all_metadata()
+ edata = self.gather_election_data(pdb)
+ opened_key = crypto.gen_opened_key(edata, md.salt)
+
+ # Use constant-time comparison to prevent timing side-channels
+ return not hmac.compare_digest(opened_key, md.opened_key)
+```
+
+**Verification:**
+
+```python
+import hmac
+import time
+import secrets
+
+stored_key = secrets.token_bytes(32)
+
+# Case 1: Keys differ in first byte
+computed_key_early = bytes([stored_key[0] ^ 0xFF]) + stored_key[1:]
+
+start = time.perf_counter_ns()
+for _ in range(100000):
+ result = not hmac.compare_digest(stored_key, computed_key_early)
+end = time.perf_counter_ns()
+time_early = end - start
+
+# Case 2: Keys differ in last byte
+computed_key_late = stored_key[:-1] + bytes([stored_key[-1] ^ 0xFF])
+
+start = time.perf_counter_ns()
+for _ in range(100000):
+ result = not hmac.compare_digest(stored_key, computed_key_late)
+end = time.perf_counter_ns()
+time_late = end - start
+
+print(f"Time for early mismatch: {time_early} ns")
+print(f"Time for late mismatch: {time_late} ns")
+print(f"Difference: {abs(time_late - time_early)} ns")
+# Should show minimal/no measurable difference
+```
+
+---
+
+## Positive Security Patterns
+
+The following security-positive implementations were identified during the audit:
+
+### 1. Strong CSPRNG Usage
+
+**Location:** `crypto.py:34-35`, throughout codebase
+**Pattern:** All random values (salts, IDs, shuffle) use Python's `secrets` module
+
+```python
+def gen_salt() -> bytes:
+ "Generate a random salt, for use in hashing."
+ return secrets.token_bytes(16)
+```
+
+**Security Benefit:** The `secrets` module is specifically designed for cryptographic randomness and is the correct choice for generating salts, tokens, and other security-sensitive random values. This prevents the use of predictable pseudo-random number generators.
+
+---
+
+### 2. Per-Voter Salt Isolation
+
+**Location:** `election.py:119-138`
+**Pattern:** Each voter/issue pair receives a unique 16-byte salt
+
+```python
+def add_salts(self, pdb):
+ assert self.is_editable()
+ for pid in self._get_voter_ids(pdb):
+ for iid in self._get_issue_ids(pdb):
+ salt = crypto.gen_salt()
+ # Store unique salt for each (voter, issue) pair
+```
+
+**Security Benefit:** Prevents vote correlation even by database administrators. Each voter's votes for different issues are cryptographically isolated, preventing linkage attacks.
+
+---
+
+### 3. Multi-Layer Key Derivation
+
+**Location:** `crypto.py:38-69`
+**Pattern:** Hierarchical key derivation chain
+
+```
+election_data → BLAKE2b → Argon2 → opened_key
+ ↓
+ (per voter/issue)
+ ↓
+ Argon2 → vote_token
+ ↓
+ HKDF → encryption_key
+```
+
+**Security Benefit:** Each layer provides cryptographic separation. Compromise of one key does not directly compromise keys at other levels. The chain uses appropriate primitives for each purpose (hashing, key derivation, key stretching).
+
+---
+
+### 4. State Machine Enforcement
+
+**Location:** `election.py:73, 259-261, 301-323`
+**Pattern:** Cryptographic operations gated by election state
+
+```python
+def open(self, pdb):
+ assert self.is_editable() # ← State check before crypto operation
+ # ... generate salts and keys ...
+
+def add_vote(self, pdb, pid, iid, votestring):
+ assert self.is_open() # ← State check before encryption
+ # ... encrypt vote ...
+
+def tally_issue(self, pdb, iid):
+ assert self.is_closed() # ← State check before decryption
+ # ... decrypt votes ...
+```
+
+**Security Benefit:** Prevents cryptographic operations in incorrect states (e.g., encrypting votes before election is open, decrypting votes before election is closed). Enforces proper lifecycle management.
+
+---
+
+### 5. Metadata Sanitization
+
+**Location:** `election.py:154-169`
+**Pattern:** Explicit exclusion of cryptographic secrets from returned data
+
+```python
+def get_metadata(self):
+ # ... retrieve election data ...
+ # NEVER return salt or opened_key
+ return ElectionMetadata(
+ # ... safe fields only ...
+ )
+
+def get_issue(self, pdb, iid):
+ # ... retrieve issue data ...
+ # Comment: "NEVER return issue.salt"
+```
+
+**Security Benefit:** Prevents accidental exposure of cryptographic material through API responses or logs. Implements principle of least privilege for data access.
+
+---
+
+### 6. Cryptographic Shuffling
+
+**Location:** `crypto.py:101-114`
+**Pattern:** Fisher-Yates shuffle with cryptographic randomness
+
+```python
+def shuffle(lst):
+ "Shuffle a list in-place, using Fisher-Yates."
+ for i in range(len(lst) - 1, 0, -1):
+ j = secrets.randbelow(i + 1) # ← CSPRNG for shuffle
+ lst[i], lst[j] = lst[j], lst[i]
+```
+
+**Security Benefit:** Vote order is randomized before tallying using cryptographically secure randomness, preventing database-order correlation attacks. Uses Fisher-Yates algorithm which provides uniform distribution.
+
+---
+
+### 7. Schema-Level Crypto Constraints
+
+**Location:** `schema.sql:81, 170, 182, 193`
+**Pattern:** Database constraints enforce cryptographic invariants
+
+```sql
+CREATE TABLE election (
+ salt BLOB CHECK(length(salt) = 16), -- ← Enforces salt length
+ opened_key BLOB CHECK(length(opened_key) = 32) -- ← Enforces key length
+);
+
+CREATE TABLE mayvote (
+ salt BLOB CHECK(length(salt) = 16) -- ← Enforces salt length
+);
+
+CREATE TABLE vote (
+ vote_token BLOB NOT NULL CHECK(length(vote_token) = 32), -- ← Enforces token length
+ ciphertext BLOB NOT NULL -- ← Enforces encryption
+);
+```
+
+**Security Benefit:** Database-level validation ensures cryptographic material always has correct lengths. Prevents truncation attacks or malformed data from entering the system.
+
+---
+
+### 8. Tamper Detection Before Tallying
+
+**Location:** `tally.py:152-154`
+**Pattern:** Integrity verification before processing sensitive operations
+
+```python
+if election.is_tampered(pdb):
+ raise ValueError(f"Election {eid} has been tampered with!")
+# Only proceed with tallying if integrity check passes
+```
+
+**Security Benefit:** Ensures election data integrity is verified before decrypting and tallying votes. Prevents processing of potentially manipulated data.
+
+---
+
+## Architecture Observations
+
+### 1. Well-Designed Key Derivation Hierarchy
+
+The hierarchical key derivation chain (`election → voter → vote`) provides appropriate cryptographic separation. Each level uses the correct primitive for its purpose:
+- **BLAKE2b** for pre-hashing large election data
+- **Argon2** for memory-hard key derivation (though variant should be changed to Argon2id)
+- **HKDF** for key stretching and domain separation
+
+This architecture demonstrates understanding of cryptographic principles and provides defense-in-depth.
+
+---
+
+### 2. Algorithm Migration Planned but Not Managed
+
+**Evidence:** Comments in `_b64_vote_key()` (lines 62-63):
+```python
+### still using Fernet now, but will switch soon. Leaving comments.
+# length=32, # 32-byte key for XChaCha20-Poly1305
+```
+
+**Observation:** The planned migration from Fernet (AES-128-CBC + HMAC-SHA256) to XChaCha20-Poly1305 is acknowledged in code comments but lacks:
+- Formal migration timeline
+- Version management strategy
+- Backward compatibility plan
+- Key rotation policy
+- Testing plan for dual-algorithm support
+
+**Impact:** Without a cryptographic inventory, this migration lacks formal tracking. The current approach (using `xchacha20_key` as the HKDF info parameter while still using Fernet) will cause issues during migration.
+
+**Recommendation:** Document the migration plan in the cryptographic inventory:
+
+```markdown
+## Algorithm Migration Plan: Fernet → XChaCha20-Poly1305
+
+| Phase | Timeline | Actions | Compatibility |
+|-------|----------|---------|---------------|
+| Current | Present | Fernet with corrected HKDF info (`fernet_vote_key_v1`) | N/A |
+| Phase 1 | Q2 2026 | Implement XChaCha20 support with distinct HKDF info (`xchacha20_vote_key_v2`) | Dual-algorithm support |
+| Phase 2 | Q3 2026 | New elections use XChaCha20 by default | Read Fernet, write XChaCha20 |
+| Phase 3 | Q1 2027 | Deprecate Fernet for new data | Read-only Fernet support |
+| Phase 4 | Q3 2027 | Remove Fernet support after all elections closed | XChaCha20 only |
+```
+
+---
+
+### 3. No PQC Readiness Documentation
+
+**ASVS Context:** The ASVS 11.1.2 section description specifically mentions:
+> "The need to future-proof cryptographic systems against the eventual rise of quantum computing is also critical. Post-Quantum Cryptography (PQC) refers to cryptographic algorithms designed to remain secure against attacks by quantum computers."
+
+**Current State:** The application's reliance on symmetric primitives (AES via Fernet, Argon2, BLAKE2b, HMAC-SHA256) provides natural resistance to quantum attacks for stored data, as Grover's algorithm only provides quadratic speedup against symmetric cryptography (effectively halving key strength).
+
+**Gap:** This quantum resistance is not documented or formally assessed. The inventory should include:
+
+```markdown
+## Post-Quantum Cryptography (PQC) Assessment
+
+| Component | Algorithm | Quantum Threat | Current Strength | PQC-Ready | Notes |
+|-----------|-----------|----------------|------------------|-----------|-------|
+| Vote Encryption | Fernet (AES-128-CBC) | Grover's algorithm | ~64-bit effective | ⚠️ Marginal | Upgrade to AES-256 recommended |
+| Key Derivation | Argon2id | Grover's algorithm | ~128-bit effective | ✅ Yes | Sufficient for PQC era |
+| Integrity (HMAC) | HMAC-SHA256 | Grover's algorithm | ~128-bit effective | ✅ Yes | Sufficient for PQC era |
+| Pre-hashing | BLAKE2b | Grover's algorithm | ~256-bit effective | ✅ Yes | Sufficient for PQC era |
+
+### Recommendations:
+1. **Immediate:** Upgrade Fernet (AES-128) to XChaCha20-Poly1305 (256-bit) for better PQC margins
+2. **Monitor:** Track NIST PQC standardization for any future asymmetric crypto needs
+3. **Policy:** Document that symmetric primitives with ≥256-bit keys are considered PQC-ready
+```
+
+---
+
+### 4. External Key Management Integration Not Audited
+
+**Evidence:** Domain context mentions "config.yaml and the asfquart secrets system" for key management, but these components were not provided for review.
+
+**Gap:** The cryptographic inventory should document:
+- How external secrets (e.g., database credentials, API keys) integrate with the cryptographic architecture
+- Whether external key management systems (KMS) are used
+- Key access controls and audit logging
+- Integration points between application crypto and infrastructure crypto
+
+**Recommendation:** Expand inventory to include external key management:
+
+```markdown
+## External Key Management Integration
+
+| System | Purpose | Key Types | Access Control | Audit Logging |
+|--------|---------|-----------|----------------|---------------|
+| config.yaml | Configuration secrets | DB credentials, API keys | File permissions | ❌ Not configured |
+| asfquart secrets | Application secrets | Session keys, CSRF tokens | Application-level | ⚠️ Unknown |
+| Database | Cryptographic material storage | Salts, opened_keys, vote_tokens | Database ACLs | ✅ Enabled |
+
+### Integration Points:
+- config.yaml secrets are NOT used for vote encryption (separation of concerns)
+- Database credentials from config.yaml protect access to cryptographic material
+- No external KMS currently integrated (future consideration)
+```
+
+---
+
+### 5. Cryptographic Agility Partially Implemented
+
+**Positive:** The codebase demonstrates some cryptographic agility:
+- Centralized crypto functions in `crypto.py` module
+- Abstraction layer between crypto operations and business logic
+- Parameterized algorithm selection (e.g., Argon2 parameters in `_hash()`)
+
+**Gap:** Lacks formal versioning and algorithm negotiation:
+- No version field in encrypted data to indicate algorithm used
+- No mechanism to support multiple algorithms simultaneously during migration
+- No rollback plan if new algorithm proves problematic
+
+**Recommendation:** Implement cryptographic versioning:
+
+```python
+# Add version prefix to ciphertext
+def create_vote_v2(vote_token: bytes, salt: bytes, votestring: str) -> bytes:
+ version = b'\x02' # Version 2: XChaCha20-Poly1305
+ vote_key = _b64_vote_key_v2(vote_token, salt)
+ cipher = XChaCha20Poly1305(vote_key)
+ nonce = secrets.token_bytes(24)
+ ciphertext = cipher.encrypt(nonce, votestring.encode("utf-8"), None)
+ return version + nonce + ciphertext
+
+def decrypt_votestring_v2(vote_token: bytes, salt: bytes, ciphertext: bytes) -> str:
+ version = ciphertext[0:1]
+ if version == b'\x01':
+ # Fernet (legacy)
+ return decrypt_votestring_v1(vote_token, salt, ciphertext[1:])
+ elif version == b'\x02':
+ # XChaCha20-Poly1305
+ nonce = ciphertext[1:25]
+ ct = ciphertext[25:]
+ vote_key = _b64_vote_key_v2(vote_token, salt)
+ cipher = XChaCha20Poly1305(vote_key)
+ plaintext = cipher.decrypt(nonce, ct, None)
+ return plaintext.decode("utf-8")
+ else:
+ raise ValueError(f"Unknown ciphertext version: {version.hex()}")
+```
+
+---
+
+## Recommendations Summary
+
+### Immediate Actions (0-30 days)
+
+| Priority | Finding | Action | Effort | Impact |
+|----------|---------|--------|--------|--------|
+| 1 | ASVS-1112-HIGH-001 | Create formal `CRYPTO_INVENTORY.md` documenting all algorithms, keys, boundaries, and lifecycle policies | Medium | High - Enables all other improvements |
+| 2 | ASVS-1112-MED-004 | Replace `!=` with `hmac.compare_digest()` in `is_tampered()` | Low | Medium - Eliminates timing side-channel |
+| 3 | ASVS-1112-MED-003 | Correct HKDF `info` parameter to `b'fernet_vote_key_v1'` | Low | Medium - Fixes inventory accuracy |
+
+### Short-Term Actions (1-3 months)
+
+| Priority | Finding | Action | Effort | Impact |
+|----------|---------|--------|--------|--------|
+| 4 | ASVS-1112-MED-002 | Change `_hash()` to use `Type.ID` (Argon2id); plan migration for existing elections | Low (code) / Medium (migration) | High - Eliminates side-channel vulnerability |
+| 5 | Architecture | Implement versioned domain separation for algorithm migration | Medium | High - Enables safe migration to XChaCha20 |
+| 6 | Architecture | Document PQC assessment confirming symmetric primitives' quantum resistance | Low | Medium - Demonstrates future-proofing |
+| 7 | Process | Establish quarterly inventory review process with documented sign-off | Low | High - Ensures ongoing compliance |
+
+### Long-Term Actions (3-12 months)
+
+| Priority | Finding | Action | Effort | Impact |
+|----------|---------|--------|--------|--------|
+| 8 | Architecture | Complete migration from Fernet to XChaCha20-Poly1305 with versioning support | High | High - Improves crypto strength and PQC readiness |
+| 9 | Architecture | Document external key management integration (config.yaml, asfquart secrets) | Medium | Medium - Completes inventory coverage |
+| 10 | Process | Integrate inventory verification into CI/CD pipeline | Medium | Medium - Prevents cryptographic drift |
+| 11 | Process | Create automated tooling to detect cryptographic API usage not documented in inventory | High | Medium - Scales inventory maintenance |
+| 12 | Architecture | Evaluate and document need for external KMS integration | Medium | Low - Future-proofs key management |
+
+---
+
+## Appendix: Files Analyzed
+
+<details>
+<summary><strong>Click to expand file list (4 files)</strong></summary>
+
+### Files Reviewed
+
+1. **`v3/schema.sql`** (Relevance: 10/10)
+ - Database schema defining cryptographic material storage
+ - Tables: `election`, `mayvote`, `vote`
+ - Cryptographic columns: `salt`, `opened_key`, `vote_token`, `ciphertext`
+ - Constraints enforcing cryptographic invariants
+
+2. **`v3/server/bin/tally.py`** (Relevance: 10/10)
+ - Vote tallying and decryption logic
+ - Tamper detection before processing
+ - Cryptographic operation orchestration
+
+3. **`v3/steve/crypto.py`** (Relevance: 10/10)
+ - Core cryptographic primitives
+ - Functions: `gen_salt()`, `gen_opened_key()`, `gen_vote_token()`, `_b64_vote_key()`, `create_vote()`, `decrypt_votestring()`, `_hash()`, `shuffle()`, `create_id()`, `benchmark_argon2()`
+ - All findings originate from this file
+
+4. **`v3/steve/election.py`** (Relevance: 10/10)
+ - Election lifecycle management
+ - Cryptographic operation consumers
+ - Functions: `open()`, `add_salts()`, `add_vote()`, `tally_issue()`, `is_tampered()`
+ - State machine enforcement for crypto operations
+
+### Files Not Analyzed (Referenced but Not Provided)
+
+- `config.yaml` — External configuration and secrets management
+- `asfquart secrets system` — Application-level secrets management
+- Test files — Unit tests for cryptographic functions (would verify algorithm behavior)
+
+</details>
+
+---
+
+**End of Report**
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