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CASAN/packages/casan-harness/scripts/bash/sign-audit-head.sh
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#!/usr/bin/env bash
set -euo pipefail
# CASAN H5 — Sign the audit chain head hash via Vault KMS (or local key fallback).
#
# Called by CI after harness tests rebuild audit.jsonl, so that
# verify-audit-chain.sh produces "anchor=signed" (not "anchor=unsigned").
#
# Usage:
# sign-audit-head.sh [audit-jsonl]
#
# Writes:
# <audit-dir>/audit-head.txt — the head hash (plain text)
# <audit-dir>/audit-head.sig — RSA signature of audit-head.txt
#
# After this script, verify-audit-chain.sh reports:
# AUDIT_CHAIN_VALID anchor=signed
#
# Environment (KMS path):
# VAULT_ADDR — e.g. http://vault:8200
# VAULT_TOKEN — token with transit/sign/casan-audit-key capability
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
source "$SCRIPT_DIR/casan-paths.sh"
PROJECT_ROOT="$CASAN_APP_ROOT"
AUDIT_LOG="${1:-$CASAN_STATE_ROOT/logs/audit/audit.jsonl}"
AUDIT_DIR="$(dirname "$AUDIT_LOG")"
HEAD_FILE="$AUDIT_DIR/audit-head.txt"
HEAD_SIG="$AUDIT_DIR/audit-head.sig"
AUDIT_PUB="$CASAN_GOVERNANCE_ROOT/audit-public.pem"
if [[ ! -f "$AUDIT_LOG" ]]; then
echo "SIGN_AUDIT_HEAD_SKIP audit.jsonl not found" >&2
exit 0
fi
# ── Compute the current chain head ────────────────────────────────────────
HEAD_HASH="$(python - "$AUDIT_LOG" <<'PY'
import hashlib, json, sys
path = sys.argv[1]
previous = ""
with open(path, encoding="utf-8") as f:
for line in f:
if not line.strip():
continue
record = json.loads(line)
if int(record.get("schema_version", 1)) >= 2:
core = "|".join([
record.get("timestamp",""), record.get("trace_id",""),
record.get("action",""), record.get("action_class",""),
record.get("actor",""), record.get("risk_level",""),
json.dumps(record.get("risk_factors", {}), sort_keys=True, separators=(",", ":")),
record.get("evidence_requirement",""), record.get("decision",""),
record.get("approval_status",""), record.get("approver",""),
record.get("input_hash",""), record.get("output_hash",""), previous,
])
else:
core = "|".join([
record.get("timestamp",""), record.get("trace_id",""),
record.get("action",""), record.get("actor",""),
record.get("risk_level",""), record.get("decision",""),
record.get("approval_status",""), record.get("approver",""),
record.get("input_hash",""), record.get("output_hash",""), previous,
])
previous = hashlib.sha256(core.encode()).hexdigest()
print(previous)
PY
)"
if [[ -z "$HEAD_HASH" ]]; then
echo "SIGN_AUDIT_HEAD_SKIP empty chain" >&2
exit 0
fi
printf '%s' "$HEAD_HASH" > "$HEAD_FILE"
# ── Sign the head file ────────────────────────────────────────────────────
VAULT_KMS="$SCRIPT_DIR/vault-kms.sh"
if [[ "${CASAN_PROFILE:-}" == "prod" || "${CASAN_PROFILE:-}" == "production" || "${CASAN_PROFILE:-}" == "strict" ]]; then
[[ "${VAULT_ADDR:-}" == https://* ]] || { echo "SIGN_AUDIT_HEAD_FAIL reason=vault_https_required_in_prod" >&2; exit 1; }
fi
if [[ -n "${VAULT_ADDR:-}" && -n "${VAULT_TOKEN:-}" ]] && \
curl -sf "$VAULT_ADDR/v1/sys/health" >/dev/null 2>&1; then
# KMS path — sign via Vault Transit, export public key
bash "$VAULT_KMS" enable-transit
bash "$VAULT_KMS" sign "$HEAD_FILE" "$HEAD_SIG" "casan-audit-key"
bash "$VAULT_KMS" pubkey "$AUDIT_PUB" "casan-audit-key"
echo "SIGN_AUDIT_HEAD_OK head=$HEAD_HASH anchor=vault-kms"
# Also re-sign the tool-calls chain head with the same Vault key so that
# verify-tool-audit.sh can verify using the same audit-public.pem.
TOOL_LOG="$AUDIT_DIR/tool-calls.jsonl"
if [[ -f "$TOOL_LOG" ]]; then
TOOL_HEAD="$(python - "$TOOL_LOG" <<'PY'
import hashlib, json, sys
prev = ""
with open(sys.argv[1], encoding="utf-8") as f:
for line in f:
if not line.strip(): continue
rec = json.loads(line)
stored = rec.pop("record_hash", "")
core = json.dumps(rec, sort_keys=True, separators=(",", ":"))
if hashlib.sha256((prev + "|" + core).encode()).hexdigest() != stored:
raise SystemExit("TOOL_CHAIN_BROKEN")
prev = stored
sys.stdout.write(prev)
PY
)"
if [[ -n "$TOOL_HEAD" ]]; then
printf '%s' "$TOOL_HEAD" > "$AUDIT_DIR/tool-calls-head.txt"
bash "$VAULT_KMS" sign "$AUDIT_DIR/tool-calls-head.txt" "$AUDIT_DIR/tool-calls-head.sig" "casan-audit-key"
echo "SIGN_TOOL_AUDIT_HEAD_OK head=$TOOL_HEAD anchor=vault-kms"
fi
fi
else
# Fallback — local key (dev environment without Vault)
if [[ "${CASAN_PROFILE:-}" == "prod" || "${CASAN_PROFILE:-}" == "production" || "${CASAN_PROFILE:-}" == "strict" ]]; then
echo "SIGN_AUDIT_HEAD_FAIL reason=vault_kms_required_in_prod" >&2
exit 1
fi
AUDIT_PRIV="$CASAN_GOVERNANCE_ROOT/audit-private.pem"
if [[ ! -f "$AUDIT_PRIV" ]]; then
echo "SIGN_AUDIT_HEAD_SKIP no private key and VAULT_ADDR not set — verify will show anchor=unsigned" >&2
exit 0
fi
openssl dgst -sha256 -sign "$AUDIT_PRIV" -out "$HEAD_SIG" "$HEAD_FILE"
echo "SIGN_AUDIT_HEAD_OK head=$HEAD_HASH anchor=local-file"
fi
# A4/V9: also bind token/cost telemetry to a signed manifest so tampering with
# provider-usage.jsonl / metrics.jsonl is detectable. Best-effort — never fails
# the audit signing step (verify-telemetry-integrity.sh is the gate).
bash "$SCRIPT_DIR/telemetry-integrity.sh" sign >/dev/null 2>&1 || true