====== Revocation Check ====== **Complexity:** Low \\ **Duration:** 30 minutes setup \\ **Goal:** Ensure CRL/OCSP availability Monitoring of revocation information (CRL and OCSP) for a functioning PKI. ---- ===== Architecture ===== flowchart LR subgraph CHECK["CHECKING"] C1[CRL Download] C2[CRL Parsing] C3[OCSP Request] end subgraph VALIDATE["VALIDATION"] V1[Signature OK?] V2[Not expired?] V3[Reachable?] end subgraph ALERT["ALERT"] A1[CRL expired] A2[OCSP Timeout] A3[CDP unreachable] end C1 --> V1 & V2 C3 --> V3 V1 -->|No| A1 V2 -->|No| A1 V3 -->|No| A2 style A1 fill:#ffebee style A2 fill:#ffebee ---- ===== CRL Monitoring ===== ==== Check CRL Status ====


#!/bin/bash
# /usr/local/bin/check-crl.sh

CRL_URLS=(
    "http://crl.example.com/intermediate.crl"
    "http://crl.example.com/root.crl"
)

WARN_HOURS=72    # Warning if < 3 days until Next Update
CRIT_HOURS=24    # Critical if < 1 day until Next Update

for url in "${CRL_URLS[@]}"; do
    echo "Checking: $url"

    # Download CRL
    crl_data=$(curl -sf --max-time 10 "$url")
    if [ $? -ne 0 ]; then
        echo "ERROR: CRL unreachable - $url"
        continue
    fi

    # Parse CRL (DER or PEM)
    if [[ "$crl_data" == *"-----BEGIN"* ]]; then
        crl_info=$(echo "$crl_data" | openssl crl -text -noout)
    else
        crl_info=$(echo "$crl_data" | openssl crl -inform DER -text -noout)
    fi

    # Extract Next Update
    next_update=$(echo "$crl_info" | grep "Next Update" | sed 's/.*: //')
    next_epoch=$(date -d "$next_update" +%s)
    now_epoch=$(date +%s)
    hours_left=$(( (next_epoch - now_epoch) / 3600 ))

    # CRL Number
    crl_number=$(echo "$crl_info" | grep -A1 "CRL Number" | tail -1 | tr -d ' ')

    # Output status
    if [ "$hours_left" -lt 0 ]; then
        echo "CRITICAL: CRL expired! - $url"
    elif [ "$hours_left" -lt "$CRIT_HOURS" ]; then
        echo "CRITICAL: CRL expires in $hours_left hours - $url"
    elif [ "$hours_left" -lt "$WARN_HOURS" ]; then
        echo "WARNING: CRL expires in $hours_left hours - $url"
    else
        echo "OK: CRL valid for $hours_left hours - $url (CRL#: $crl_number)"
    fi

    # Count revoked certificates
    revoked_count=$(echo "$crl_info" | grep -c "Serial Number:")
    echo "  Revoked: $revoked_count certificates"
    echo ""
done

==== Prometheus Exporter for CRL ====


#!/bin/bash
# crl-exporter.sh - Generates Prometheus metrics

METRICS_FILE="/var/lib/node_exporter/textfile_collector/crl.prom"

cat /dev/null > "$METRICS_FILE"

CRL_URLS=(
    "intermediate|http://crl.example.com/intermediate.crl"
    "root|http://crl.example.com/root.crl"
)

for entry in "${CRL_URLS[@]}"; do
    IFS='|' read -r name url <<< "$entry"

    crl_data=$(curl -sf --max-time 10 "$url" 2>/dev/null)
    if [ $? -ne 0 ]; then
        echo "crl_reachable{name=\"$name\"} 0" >> "$METRICS_FILE"
        continue
    fi

    echo "crl_reachable{name=\"$name\"} 1" >> "$METRICS_FILE"

    next_update=$(echo "$crl_data" | openssl crl -inform DER -nextupdate -noout 2>/dev/null | cut -d= -f2)
    if [ -n "$next_update" ]; then
        next_epoch=$(date -d "$next_update" +%s)
        echo "crl_next_update_timestamp{name=\"$name\"} $next_epoch" >> "$METRICS_FILE"
    fi

    revoked=$(echo "$crl_data" | openssl crl -inform DER -text -noout 2>/dev/null | grep -c "Serial Number:")
    echo "crl_revoked_count{name=\"$name\"} $revoked" >> "$METRICS_FILE"
done

**Alert Rule:**


- alert: CRLExpiringSoon
  expr: crl_next_update_timestamp - time() < 86400
  labels:
    severity: critical
  annotations:
    summary: "CRL {{ $labels.name }} expires in < 24h"

- alert: CRLUnreachable
  expr: crl_reachable == 0
  for: 5m
  labels:
    severity: critical
  annotations:
    summary: "CRL {{ $labels.name }} unreachable"

---- ===== OCSP Monitoring ===== ==== Check OCSP Responder ====


#!/bin/bash
# /usr/local/bin/check-ocsp.sh

OCSP_URL="http://ocsp.example.com"
ISSUER_CERT="/etc/pki/CA/intermediate-ca.pem"
TEST_CERT="/etc/ssl/certs/test-server.pem"

echo "OCSP Responder Check: $OCSP_URL"

# Send OCSP request
start_time=$(date +%s%N)
response=$(openssl ocsp \
    -issuer "$ISSUER_CERT" \
    -cert "$TEST_CERT" \
    -url "$OCSP_URL" \
    -resp_text 2>&1)
end_time=$(date +%s%N)

# Calculate response time (ms)
response_time=$(( (end_time - start_time) / 1000000 ))

# Extract status
if echo "$response" | grep -q "good"; then
    status="good"
elif echo "$response" | grep -q "revoked"; then
    status="revoked"
else
    status="error"
fi

# Output
echo "Status: $status"
echo "Response time: ${response_time}ms"

if [ "$status" = "error" ]; then
    echo "ERROR: OCSP Responder not functional"
    exit 1
fi

if [ "$response_time" -gt 2000 ]; then
    echo "WARNING: OCSP response time > 2s"
fi

==== OCSP Prometheus Exporter ====


#!/bin/bash
# ocsp-exporter.sh

METRICS_FILE="/var/lib/node_exporter/textfile_collector/ocsp.prom"

OCSP_ENDPOINTS=(
    "intermediate|http://ocsp.example.com|/etc/pki/CA/intermediate.pem|/etc/ssl/certs/test.pem"
)

cat /dev/null > "$METRICS_FILE"

for entry in "${OCSP_ENDPOINTS[@]}"; do
    IFS='|' read -r name url issuer cert <<< "$entry"

    start_time=$(date +%s%N)
    response=$(openssl ocsp -issuer "$issuer" -cert "$cert" -url "$url" -resp_text 2>&1)
    exit_code=$?
    end_time=$(date +%s%N)

    response_time=$(( (end_time - start_time) / 1000000 ))
    echo "ocsp_response_time_ms{name=\"$name\"} $response_time" >> "$METRICS_FILE"

    if [ $exit_code -eq 0 ]; then
        echo "ocsp_up{name=\"$name\"} 1" >> "$METRICS_FILE"
    else
        echo "ocsp_up{name=\"$name\"} 0" >> "$METRICS_FILE"
    fi

    if echo "$response" | grep -q "good"; then
        echo "ocsp_status{name=\"$name\"} 0" >> "$METRICS_FILE"  # 0=good
    elif echo "$response" | grep -q "revoked"; then
        echo "ocsp_status{name=\"$name\"} 1" >> "$METRICS_FILE"  # 1=revoked
    else
        echo "ocsp_status{name=\"$name\"} 2" >> "$METRICS_FILE"  # 2=unknown/error
    fi
done

**Alert Rules:**


- alert: OCSPResponderDown
  expr: ocsp_up == 0
  for: 2m
  labels:
    severity: critical
  annotations:
    summary: "OCSP Responder {{ $labels.name }} unreachable"

- alert: OCSPResponseSlow
  expr: ocsp_response_time_ms > 2000
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: "OCSP {{ $labels.name }} slow: {{ $value }}ms"

---- ===== Blackbox Exporter =====


# blackbox.yml
modules:
  tls_connect:
    prober: tcp
    timeout: 5s
    tcp:
      tls: true
      tls_config:
        insecure_skip_verify: false

  http_crl:
    prober: http
    timeout: 10s
    http:
      method: GET
      valid_status_codes: [200]
      fail_if_body_not_matches_regexp: ["-----BEGIN X509 CRL-----|^\x30"]

  ocsp_check:
    prober: http
    timeout: 5s
    http:
      method: POST
      headers:
        Content-Type: application/ocsp-request

---- ===== PowerShell (Windows) =====


# Check-Revocation.ps1

param(
    [string]$OcspUrl = "http://ocsp.example.com",
    [string]$CrlUrl = "http://crl.example.com/intermediate.crl"
)

# Check CRL
Write-Host "=== CRL Check ===" -ForegroundColor Cyan
try {
    $crlResponse = Invoke-WebRequest -Uri $CrlUrl -TimeoutSec 10
    Write-Host "CRL reachable: OK ($($crlResponse.StatusCode))" -ForegroundColor Green

    # Parse CRL (requires additional tools or .NET)
    $crlBytes = $crlResponse.Content
    # ... CRL parsing here
}
catch {
    Write-Host "CRL ERROR: $_" -ForegroundColor Red
}

# Check OCSP (simplified via openssl)
Write-Host "`n=== OCSP Check ===" -ForegroundColor Cyan
try {
    $certPath = "C:\certs\test.pem"
    $issuerPath = "C:\certs\intermediate.pem"

    $ocspResult = & openssl ocsp -issuer $issuerPath -cert $certPath -url $OcspUrl -text 2>&1
    if ($ocspResult -match "good") {
        Write-Host "OCSP Status: GOOD" -ForegroundColor Green
    }
    elseif ($ocspResult -match "revoked") {
        Write-Host "OCSP Status: REVOKED" -ForegroundColor Yellow
    }
    else {
        Write-Host "OCSP Status: ERROR" -ForegroundColor Red
    }
}
catch {
    Write-Host "OCSP ERROR: $_" -ForegroundColor Red
}

---- ===== Checklist ===== | # | Checkpoint | Done | |---|------------|------| | 1 | CRL URLs defined | | | 2 | CRL download working | | | 3 | CRL expiry warning configured | | | 4 | OCSP URL defined | | | 5 | OCSP response working | | | 6 | Prometheus exporter active | | | 7 | Alerts configured | | ---- ===== Related Documentation ===== * [[..:tagesgeschaeft:zertifikat-widerrufen|Revoke Certificate]] - Update CRL * [[.:ablauf-monitoring|Expiry Monitoring]] - Certificate expiry * [[en:int:pqcrypt:szenarien:widerruf:start|Revocation Scenarios]] - Detailed guides ---- << [[.:ablauf-monitoring|<- Expiry Monitoring]] | [[.:audit-logging|-> Audit Logging]] >> ---- //Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional// {{tag>monitoring crl ocsp revocation operator}}