1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275//! Merkle hash chain audit trail for security-critical actions.
//!
//! Every auditable event is appended to an append-only log where each entry
//! contains the SHA-256 hash of its own contents concatenated with the hash of
//! the previous entry, forming a tamper-evident chain (similar to a blockchain).
use chrono::Utc;
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::sync::Mutex;
/// Categories of auditable actions within the agent runtime.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum AuditAction {
ToolInvoke,
CapabilityCheck,
AgentSpawn,
AgentKill,
AgentMessage,
MemoryAccess,
FileAccess,
NetworkAccess,
ShellExec,
AuthAttempt,
WireConnect,
ConfigChange,
}
impl std::fmt::Display for AuditAction {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "{:?}", self)
}
}
/// A single entry in the Merkle hash chain audit log.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AuditEntry {
/// Monotonically increasing sequence number (0-indexed).
pub seq: u64,
/// ISO-8601 timestamp of when this entry was recorded.
pub timestamp: String,
/// The agent that triggered (or is the subject of) this action.
pub agent_id: String,
/// The category of action being audited.
pub action: AuditAction,
/// Free-form detail about the action (e.g. tool name, file path).
pub detail: String,
/// The outcome of the action (e.g. "ok", "denied", an error message).
pub outcome: String,
/// SHA-256 hash of the previous entry (or all-zeros for the genesis).
pub prev_hash: String,
/// SHA-256 hash of this entry's content concatenated with `prev_hash`.
pub hash: String,
}
/// Computes the SHA-256 hash for a single audit entry from its fields.
fn compute_entry_hash(
seq: u64,
timestamp: &str,
agent_id: &str,
action: &AuditAction,
detail: &str,
outcome: &str,
prev_hash: &str,
) -> String {
let mut hasher = Sha256::new();
hasher.update(seq.to_string().as_bytes());
hasher.update(timestamp.as_bytes());
hasher.update(agent_id.as_bytes());
hasher.update(action.to_string().as_bytes());
hasher.update(detail.as_bytes());
hasher.update(outcome.as_bytes());
hasher.update(prev_hash.as_bytes());
hex::encode(hasher.finalize())
}
/// An append-only, tamper-evident audit log using a Merkle hash chain.
///
/// Thread-safe — all access is serialised through internal mutexes.
pub struct AuditLog {
entries: Mutex<Vec<AuditEntry>>,
tip: Mutex<String>,
}
impl AuditLog {
/// Creates a new empty audit log.
///
/// The initial tip hash is 64 zero characters (the "genesis" sentinel).
pub fn new() -> Self {
Self {
entries: Mutex::new(Vec::new()),
tip: Mutex::new("0".repeat(64)),
}
}
/// Records a new auditable event and returns the SHA-256 hash of the entry.
///
/// The entry is atomically appended to the chain with the current tip as
/// its `prev_hash`, and the tip is advanced to the new hash.
pub fn record(
&self,
agent_id: impl Into<String>,
action: AuditAction,
detail: impl Into<String>,
outcome: impl Into<String>,
) -> String {
let agent_id = agent_id.into();
let detail = detail.into();
let outcome = outcome.into();
let timestamp = Utc::now().to_rfc3339();
let mut entries = self.entries.lock().unwrap_or_else(|e| e.into_inner());
let mut tip = self.tip.lock().unwrap_or_else(|e| e.into_inner());
let seq = entries.len() as u64;
let prev_hash = tip.clone();
let hash = compute_entry_hash(
seq, ×tamp, &agent_id, &action, &detail, &outcome, &prev_hash,
);
entries.push(AuditEntry {
seq,
timestamp,
agent_id,
action,
detail,
outcome,
prev_hash,
hash: hash.clone(),
});
*tip = hash.clone();
hash
}
/// Walks the entire chain and recomputes every hash to detect tampering.
///
/// Returns `Ok(())` if the chain is intact, or `Err(msg)` describing
/// the first inconsistency found.
pub fn verify_integrity(&self) -> Result<(), String> {
let entries = self.entries.lock().unwrap_or_else(|e| e.into_inner());
let mut expected_prev = "0".repeat(64);
for entry in entries.iter() {
if entry.prev_hash != expected_prev {
return Err(format!(
"chain break at seq {}: expected prev_hash {} but found {}",
entry.seq, expected_prev, entry.prev_hash
));
}
let recomputed = compute_entry_hash(
entry.seq,
&entry.timestamp,
&entry.agent_id,
&entry.action,
&entry.detail,
&entry.outcome,
&entry.prev_hash,
);
if recomputed != entry.hash {
return Err(format!(
"hash mismatch at seq {}: expected {} but found {}",
entry.seq, recomputed, entry.hash
));
}
expected_prev = entry.hash.clone();
}
Ok(())
}
/// Returns the current tip hash (the hash of the most recent entry,
/// or the genesis sentinel if the log is empty).
pub fn tip_hash(&self) -> String {
self.tip.lock().unwrap_or_else(|e| e.into_inner()).clone()
}
/// Returns the number of entries in the log.
pub fn len(&self) -> usize {
self.entries.lock().unwrap_or_else(|e| e.into_inner()).len()
}
/// Returns whether the log is empty.
pub fn is_empty(&self) -> bool {
self.entries
.lock()
.unwrap_or_else(|e| e.into_inner())
.is_empty()
}
/// Returns up to the most recent `n` entries (cloned).
pub fn recent(&self, n: usize) -> Vec<AuditEntry> {
let entries = self.entries.lock().unwrap_or_else(|e| e.into_inner());
let start = entries.len().saturating_sub(n);
entries[start..].to_vec()
}
}
impl Default for AuditLog {
fn default() -> Self {
Self::new()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_audit_chain_integrity() {
let log = AuditLog::new();
log.record(
"agent-1",
AuditAction::ToolInvoke,
"read_file /etc/passwd",
"ok",
);
log.record("agent-1", AuditAction::ShellExec, "ls -la", "ok");
log.record("agent-2", AuditAction::AgentSpawn, "spawning helper", "ok");
log.record(
"agent-1",
AuditAction::NetworkAccess,
"https://example.com",
"denied",
);
assert_eq!(log.len(), 4);
assert!(log.verify_integrity().is_ok());
// Verify the chain links are correct
let entries = log.recent(4);
assert_eq!(entries[0].prev_hash, "0".repeat(64));
assert_eq!(entries[1].prev_hash, entries[0].hash);
assert_eq!(entries[2].prev_hash, entries[1].hash);
assert_eq!(entries[3].prev_hash, entries[2].hash);
}
#[test]
fn test_audit_tamper_detection() {
let log = AuditLog::new();
log.record("agent-1", AuditAction::ToolInvoke, "read_file /tmp/a", "ok");
log.record("agent-1", AuditAction::ShellExec, "rm -rf /", "denied");
log.record("agent-1", AuditAction::MemoryAccess, "read key foo", "ok");
// Tamper with an entry
{
let mut entries = log.entries.lock().unwrap();
entries[1].detail = "echo hello".to_string(); // change the detail
}
let result = log.verify_integrity();
assert!(result.is_err());
assert!(result.unwrap_err().contains("hash mismatch at seq 1"));
}
#[test]
fn test_audit_tip_changes() {
let log = AuditLog::new();
let genesis_tip = log.tip_hash();
assert_eq!(genesis_tip, "0".repeat(64));
let h1 = log.record("a", AuditAction::AgentSpawn, "spawn", "ok");
assert_eq!(log.tip_hash(), h1);
assert_ne!(log.tip_hash(), genesis_tip);
let h2 = log.record("b", AuditAction::AgentKill, "kill", "ok");
assert_eq!(log.tip_hash(), h2);
assert_ne!(h2, h1);
}
}