Inhaltsverzeichnis

Revocation-Check

Komplexität: Niedrig
Dauer: 30 Minuten Setup
Ziel: CRL/OCSP Verfügbarkeit sicherstellen

Überwachung der Widerrufsinformation (CRL und OCSP) für eine funktionierende PKI.

Architektur

flowchart LR subgraph CHECK["🔍 PRÜFUNG"] C1[CRL Download] C2[CRL Parsing] C3[OCSP Request] end subgraph VALIDATE["✅ VALIDIERUNG"] V1[Signatur OK?] V2[Nicht abgelaufen?] V3[Erreichbar?] end subgraph ALERT["🚨 ALERT"] A1[CRL abgelaufen] A2[OCSP Timeout] A3[CDP nicht erreichbar] end C1 --> V1 & V2 C3 --> V3 V1 -->|Nein| A1 V2 -->|Nein| A1 V3 -->|Nein| A2 style A1 fill:#ffebee style A2 fill:#ffebee

CRL Monitoring

CRL Status prüfen

#!/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    # Warnung wenn < 3 Tage bis Next Update
CRIT_HOURS=24    # Kritisch wenn < 1 Tag bis Next Update
 
for url in "${CRL_URLS[@]}"; do
    echo "Prüfe: $url"
 
    # CRL herunterladen
    crl_data=$(curl -sf --max-time 10 "$url")
    if [ $? -ne 0 ]; then
        echo "FEHLER: CRL nicht erreichbar - $url"
        continue
    fi
 
    # CRL parsen (DER oder 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
 
    # Next Update extrahieren
    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 ' ')
 
    # Status ausgeben
    if [ "$hours_left" -lt 0 ]; then
        echo "KRITISCH: CRL abgelaufen! - $url"
    elif [ "$hours_left" -lt "$CRIT_HOURS" ]; then
        echo "KRITISCH: CRL läuft in $hours_left Stunden ab - $url"
    elif [ "$hours_left" -lt "$WARN_HOURS" ]; then
        echo "WARNUNG: CRL läuft in $hours_left Stunden ab - $url"
    else
        echo "OK: CRL gültig für $hours_left Stunden - $url (CRL#: $crl_number)"
    fi
 
    # Anzahl widerrufener Zertifikate
    revoked_count=$(echo "$crl_info" | grep -c "Serial Number:")
    echo "  Widerrufen: $revoked_count Zertifikate"
    echo ""
done

Prometheus Exporter für CRL

#!/bin/bash
# crl-exporter.sh - Generiert Prometheus-Metriken
 
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 }} läuft in < 24h ab"

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

OCSP Monitoring

OCSP Responder prüfen

#!/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"
 
# OCSP Request senden
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)
 
# Response-Zeit berechnen (ms)
response_time=$(( (end_time - start_time) / 1000000 ))
 
# Status extrahieren
if echo "$response" | grep -q "good"; then
    status="good"
elif echo "$response" | grep -q "revoked"; then
    status="revoked"
else
    status="error"
fi
 
# Ausgabe
echo "Status: $status"
echo "Response-Zeit: ${response_time}ms"
 
if [ "$status" = "error" ]; then
    echo "FEHLER: OCSP Responder nicht funktionsfähig"
    exit 1
fi
 
if [ "$response_time" -gt 2000 ]; then
    echo "WARNUNG: OCSP Response-Zeit > 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 }} nicht erreichbar"

- alert: OCSPResponseSlow
  expr: ocsp_response_time_ms > 2000
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: "OCSP {{ $labels.name }} langsam: {{ $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"
)
 
# CRL prüfen
Write-Host "=== CRL Check ===" -ForegroundColor Cyan
try {
    $crlResponse = Invoke-WebRequest -Uri $CrlUrl -TimeoutSec 10
    Write-Host "CRL erreichbar: OK ($($crlResponse.StatusCode))" -ForegroundColor Green
 
    # CRL parsen (erfordert zusätzliche Tools oder .NET)
    $crlBytes = $crlResponse.Content
    # ... CRL-Parsing hier
}
catch {
    Write-Host "CRL FEHLER: $_" -ForegroundColor Red
}
 
# OCSP prüfen (vereinfacht 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 FEHLER: $_" -ForegroundColor Red
}

Checkliste

# Prüfpunkt ✓
————–—
1 CRL-URLs definiert ☐
2 CRL-Download funktioniert ☐
3 CRL-Ablaufwarnung konfiguriert ☐
4 OCSP-URL definiert ☐
5 OCSP-Response funktioniert ☐
6 Prometheus Exporter aktiv ☐
7 Alerts konfiguriert ☐

Verwandte Dokumentation

« ← Ablauf-Monitoring | → Audit-Logging »

Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional

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