tessera-ctl/apps/api/src/cert-manager/cert-csr.ts

import { createPublicKey } from 'node:crypto';
import * as forge from 'node-forge';
import { describeKey, keyIdOf, sha256Hex, spkiDerOf } from './cert-keys';
import { safeBaseName } from './cert-names';
import type { CsrItem, ItemSource } from './cert-types';

/**
 * Zertifikatsanfragen (CSR) des Zertifikat-Managers (quick-261009-ikt, D-05, D-16).
 *
 * Die CSR-Leser von forge koennen nur RSA. Darum wird der ASN.1-Aufbau selbst gelesen
 * (CertificationRequestInfo: Version, Inhaber, oeffentlicher Schluessel, Attribute) und der
 * Schluessel an node:crypto gegeben. Die Selbstunterschrift wird nicht geprueft: die Anfrage
 * dient hier nur der Anzeige und der Zuordnung zu Zertifikat und Schluessel.
 */

const OID_EXTENSION_REQUEST = '1.2.840.113549.1.9.14';
const OID_SUBJECT_ALT_NAME = '2.5.29.17';

type Asn1 = forge.asn1.Asn1;

function children(node: Asn1): Asn1[] {
  return Array.isArray(node.value) ? (node.value as Asn1[]) : [];
}

function readAsn1(der: Buffer): Asn1 {
  // Typdefinition kennt nur `strict: boolean`; decodeBitStrings aus, damit der Schluessel
  // (SPKI) beim erneuten Schreiben Byte fuer Byte dem Original entspricht.
  const options = { decodeBitStrings: false } as unknown as boolean;
  return forge.asn1.fromDer(forge.util.createBuffer(der.toString('binary')), options);
}

function toBuffer(node: Asn1): Buffer {
  return Buffer.from(forge.asn1.toDer(node).getBytes(), 'binary');
}

interface ParsedRequest {
  subject: Asn1;
  spki: Asn1;
  attributes: Asn1 | null;
}

/** Prueft den Aufbau streng genug, dass weder ein Zertifikat noch ein Schluessel als CSR durchgeht. */
function parseRequest(der: Buffer): ParsedRequest {
  const root = readAsn1(der);
  const [info, algorithm, signature] = children(root);
  if (
    root.type !== forge.asn1.Type.SEQUENCE ||
    children(root).length !== 3 ||
    algorithm.type !== forge.asn1.Type.SEQUENCE ||
    signature.type !== forge.asn1.Type.BITSTRING ||
    info.type !== forge.asn1.Type.SEQUENCE
  ) {
    throw new Error('not a certification request');
  }
  const [version, subject, spki, attributes] = children(info);
  if (
    version?.type !== forge.asn1.Type.INTEGER ||
    version.value !== '\x00' ||
    subject?.type !== forge.asn1.Type.SEQUENCE ||
    spki?.type !== forge.asn1.Type.SEQUENCE ||
    children(spki).length !== 2 ||
    children(spki)[1].type !== forge.asn1.Type.BITSTRING
  ) {
    throw new Error('not a certification request');
  }
  const hasAttributes =
    attributes?.tagClass === forge.asn1.Class.CONTEXT_SPECIFIC && attributes.type === 0;
  return { subject, spki, attributes: hasAttributes ? attributes : null };
}

function formatIp(bytes: string): string | null {
  if (bytes.length === 4) return [...bytes].map((c) => c.charCodeAt(0)).join('.');
  if (bytes.length === 16) {
    const groups: string[] = [];
    for (let i = 0; i < 16; i += 2) {
      groups.push(
        ((bytes.charCodeAt(i) << 8) | bytes.charCodeAt(i + 1)).toString(16).toUpperCase(),
      );
    }
    return groups.join(':');
  }
  return null;
}

/** SAN aus dem Attribut „extensionRequest“: DNS-Namen unveraendert, IP-Adressen mit Praefix 'IP:'. */
function sanOf(attributes: Asn1 | null): string[] {
  const names: string[] = [];
  if (!attributes) return names;
  for (const attribute of children(attributes)) {
    const [oid, set] = children(attribute);
    if (!oid || oid.type !== forge.asn1.Type.OID) continue;
    if (forge.asn1.derToOid(oid.value as string) !== OID_EXTENSION_REQUEST) continue;
    const extensionList = children(set ?? attribute)[0];
    const extensions = extensionList ? children(extensionList) : [];
    for (const extension of extensions) {
      const parts = children(extension);
      if (parts[0]?.type !== forge.asn1.Type.OID) continue;
      if (forge.asn1.derToOid(parts[0].value as string) !== OID_SUBJECT_ALT_NAME) continue;
      const octets = parts[parts.length - 1];
      if (octets?.type !== forge.asn1.Type.OCTETSTRING) continue;
      const generalNames = forge.asn1.fromDer(forge.util.createBuffer(octets.value as string));
      for (const name of children(generalNames)) {
        if (name.tagClass !== forge.asn1.Class.CONTEXT_SPECIFIC) continue;
        if (name.type === 2) names.push(name.value as string); // dNSName
        if (name.type === 7) {
          const ip = formatIp(name.value as string); // iPAddress
          if (ip) names.push(`IP:${ip}`);
        }
      }
    }
  }
  return names;
}

/** forge.pki.RDNAttributesAsArray fehlt in den Typdefinitionen, ist aber Teil von forge (liest nur den Namen). */
const rdnAttributesAsArray = (
  forge.pki as unknown as {
    RDNAttributesAsArray(rdn: Asn1): { shortName?: string; value: unknown }[];
  }
).RDNAttributesAsArray;

function rdnValue(subject: Asn1, shortName: string): string {
  const attributes = rdnAttributesAsArray(subject);
  const found = attributes.find((a) => a.shortName === shortName);
  return typeof found?.value === 'string' ? found.value : '';
}

function pemOf(der: Buffer): string {
  const lines = der.toString('base64').match(/.{1,64}/g) ?? [];
  return `-----BEGIN CERTIFICATE REQUEST-----\n${lines.join('\n')}\n-----END CERTIFICATE REQUEST-----\n`;
}

/** Baut den Eintrag aus einem DER-CSR. Wirft, wenn es keine Zertifikatsanfrage ist. `keyId` setzt matchKeys. */
export function csrItemFromDer(der: Buffer, source: ItemSource): CsrItem {
  const request = parseRequest(der);
  const publicKey = createPublicKey({ key: toBuffer(request.spki), format: 'der', type: 'spki' });
  const details = describeKey(publicKey);
  const cn = rdnValue(request.subject, 'CN');
  return {
    id: `r-${sha256Hex(der).slice(0, 16)}`,
    kind: 'csr',
    sources: [{ ...source }],
    pem: pemOf(der),
    baseName: safeBaseName(cn, 'anfrage'),
    cn,
    organization: rdnValue(request.subject, 'O'),
    san: sanOf(request.attributes),
    keyType: details.keyType,
    keyBits: details.keyBits,
    curve: details.curve,
    keyId: null,
    certIds: [],
  };
}

/** Kennung des Schluessels einer Anfrage (aus dem PEM des Eintrags), fuer die Zuordnung. */
export function csrPublicKeyOf(pem: string): { id: string; spki: Buffer } {
  const body = pem.replace(/-----(BEGIN|END) CERTIFICATE REQUEST-----/g, '').replace(/\s+/g, '');
  const request = parseRequest(Buffer.from(body, 'base64'));
  const publicKey = createPublicKey({ key: toBuffer(request.spki), format: 'der', type: 'spki' });
  return { id: keyIdOf(publicKey), spki: spkiDerOf(publicKey) };
}