WWUCA - Certification Authority of the Münster University

• Rainer Perske

• Westfälische Wilhelms-Universität
  Zentrum für Informationsverarbeitung
  Zertifizierungsstelle
  Röntgenstraße 7-13
  48149 Münster

• ca@uni-muenster.de
  +49 251 83 31590 (fon)
  +49 251 83 31555 (fax)

Certificate (simplified example)

• Public Key: Algorithm RSA, Exponent 65537; Modulus e3 d2 10 ... 50 4a 85

• Subject (certificate owner): CN=Rainer Perske, O=Universitaet Muenster, C=DE

• Issuer (certification authority): CN=Zertifizierungsstelle, O=Universitaet Muenster, C=DE

• Serial number: 13:95:13:C7:CD:EA:2E; version: 3 (has extensions)

• Valid from 2012-03-30 11:17:11 UTC to 2015-03-30 11:17:11 UTC

• Extension: Usage: signing, key encryption (for mail, TLS, Smartcard-Login), but not as CA

• Extension: Alternative names: E-Mail perske@uni-muenster.de, Login: perske (uni-muenster.de)

• Signature for all data above, created with the private key of the certification authority:
  Algorithm: PKCS #1 SHA-1 with RSA, value: 81 5c 3e ... a8 eb 40

• The certificate does not contain the owner's private key!

Certification hierarchy

• The certificate of Rainer Perske is signed by the Zertifizierungsstelle der Universität Münster
  (WWU Certification Authority, WWUCA)

• The WWUCA is an intermediate CA because ...

• The certificate of the WWUCA is signed by the DFN Public Key Infrastructure (DFN-PKI) “Global” CA
  (DFN = Deutsches Forschungsnetz = German Research Network)

• The DFN-PKI “Global” CA is an intermediate CA because ...

• The certificate of the DFN-PKI “Global” CA is signed by the “Deutsche Telekom Root CA 2”

• The “Deutsche Telekom Root CA 2” is a root CA because ...

• The certificate of the “Deutsche Telekom Root CA 2” is signed by itself.

Rainer Perske   ⇐   WWUCA   ⇐   DFN-PKI “Global” CA   ⇐   Deutsche Telekom Root CA 2

Why do we use this hierarchy with DFN-PKI “Global”?

• The “Deutsche Telekom Root CA 2” certificate is part of nearly all browsers and e-mail programs

• Thus nearly all e-mail programs can check our e-mail signatures automatically
  and all browsers accept our server certificates automatically

• Recipients of our e-mails or users connecting to our servers do not receive boring warnings

• Demo: Firefox: Edit the CA certificate of “Deutsche Telekom Root CA 2”

WWUCA

• 4 staff members (at ZIV) + 5 further team members (spread over WWU and UKM)

• I spend about 10 % of my time for the WWUCA, all others far less.

• X.509 certificates issued by the WWUCA (all in the DFN-PKI “Global” hierarchy):
  valid certificates: 920: 450 server, 450 persons, 10 group, 10 team member
  issued certificates per year: 100 for servers, 160 for persons, 40 revocations

• Other DFN-PKI hierarchies:
  DFN-PKI “Basic” (relaxed identity check; not in browsers): no demand
  DFN-PKI “Grid” (for scientific grid computing): registration only, one certificate per year
  DFN-PKI “SLCS“ (Short-Lived Credential Service): no demand

• OpenPGP discontinued: Less than 15 certificates per year

DFN PKI

• Service of the German Research Network provided by DFN CERT GmbH in Hamburg

• 6 full time team members operate and develop DFN-PKI

  • 5 X.509 hierarchies with different policies (“Classic”, “Global“, “Basic”, “Grid”, “SLCS“)

  • 300+ outsourced subordinate CAs of DFN e.V. members (incl. WWUCA)

  • OpenPGP discontinued due to lack of demand

• No additional costs: DFN PKI service is part of the DFN Internet service

  • WWU + UKM + KA + FH + MPI together pay 250.000 €/a for 2×2 GBit/s cluster connectivity

Requesting a user certificate from the WWUCA

• Generate a key pair

• Upload public key + personal data, signed with the private key, to the WWUCA

• Print the application form containing the fingerprint of the public key and further data

• All above in one step: http://ca.wwu.de ⇒ Nutzerzertifikat

• Sign the form and thus declare that the public key is really yours

• Hand out the form to a WWUCA team member, presenting a proof of identity
  (identity card or passport, no driving license, no student card)

• The WWUCA never sees your private key (is no »trust center«)

Keeping your private key safe

• Beneath all usual measures to protect computer and password

• Use dedicated browser instance / virtual machine for sensitive applications

• Always protect your private key by encrypting with a password resp. PIN
  (Firefox: Set master password before key generation, always encrypt PKCS#12 backup files with a password!)

• Always encrypt the medium containing your private key, too.

• For authentication purposes, better use hardware device (smartcard, eToken, nPA) with a PIN.

  • (But think twice for e-mail purposes: you cannot read old e-mails any longer if you loose a your private key)

• Always keep in mind: Your private key is only needed when signing and when decrypting, never else.

• Get paranoid. Even more paranoid. “Social Engeneering” is the most successful way of attacking.

Certification process (1)

• The WWUCA team member:

  • strictly obeys Certificate Policy (CP) and Certification Practice Statement (CPS)
    (Rules for security, target audience, privacy, methods, archiving, contents, life times, revocations etc.)
    CP: https://www.pki.dfn.de/fileadmin/PKI/DFN-PKI_CP.pdf
    CPS: https://www.pki.dfn.de/fileadmin/PKI/DFN-PKI_CPS.pdf

  • checks all aspects of your request (perhaps applies corrections or rejects)

  • adds some data (Subject Alternative Names): e-mail addresses, login name, ...

  • compares the fingerprint on the form with that of the public key
    (thus the WWUCA knows the public key with the given fingerprint is yours)

  • (electronically) signs a confirmation message to the certification server

  • (manually) signs and archives your request form

Certification process (2)

• The DFN PKI certification server in Hamburg automatically:

  • checks the signature of the message and the accreditation of the signer

  • checks conformance of the request (only our domains? etc.)

  • creates the certificate

  • mails the certificate to the requester

  • publishes the certificate via LDAP (if requested)

    • Use as addressbook: ldap.pca.dfn.de:389, Base-DN: O=DFN-Verein,C=DE

    • Thunderbird: Bearbeiten | Einstellungen | Verfassen | Adressieren | LDAP-Verzeichnisserver | Bearbeiten | Hinzufügen ...

X.500 DNs in WWUCA certificates

• Several restrictions by CP+CPS (most of them technically enforced by DFN PKI):

• only servers and e-mail addresses belonging to WWU, UKM, or KA

• emailAddress=. . . (at most one may be given, but see below)
  CN=. . . (exactly one must be given; only name parts from identity card, no “Prof.“ or alike)
  OU=. . . (at most one may be given, avoid abbreviations)
  O=Universitaet Muenster (or) O=Universitaetsklinikum Muenster (or) O=Kunstakademie Muenster (must be given)
  L=Muenster (and) ST=Nordrhein-Westfalen (optional for users; must be given for servers)
  C=DE (must be given)

• Limited character set for CN/OU/O/L/ST/C: a-z A-Z 0-9 '()+,-./:=? space; limited field length (64)
  Convert german letters: ä ö ü ß Ä Ö Ü ⇒ ae oe ue ss Ae Oe Ue,
  Remove accents: Ibáñez ⇒ Ibanez, Łódź ⇒ Lodz
  Phonetically transcribe other scripts (phonetically): Δήμητρα ⇒ Dimitra, Ærøskøbing ⇒ Aeroeskoebing

• Order matters and no other fields allowed

• E-mail addresses, login names etc. can be given als Subject Alternative Name, but must be verified

Presenting a certificate

• You present your certificate (and all intermediate certificates):

  • As a person/group: when sending a signed e-mail (attached to the signature)

    • The recipient will check signature and certificate

  • As a server: when accepting an HTTPS (IMAPS, POP3S, ...) connection

    • The client will check the certificate and compare the host name

  • As a client: when connecting to an HTTPS (IMAPS, POP3S, ...) server

    • Only if expected by the server (better security than password authentification)

    • The server will check the certificate

    • Try: https://xsso.uni-muenster.de/MeinZIV/

Verifying a certificate

• For checking certificates you need the corresponding root certificate

• Many root certificates are pre-installed in your software, but can be edited

  • The CA/Browser Forum recommends requirements for CAs whose root certificates are built in

• Verifying certificates = (automatically)

  • comparing identity in certificate with e-mail partner resp. hostname

    • Hosts and domains are case-insensitive but local parts of e-mail addresses are case-sensitive:
      perske@wwu.de   =   perske@WWU.DE   ≠   Perske@WWU.DE

    • Always use lowercase only, both in certificates and in your e-mail configuration

  • checking all ( signature + purpose + life time + more ) of each certificate involved

  • checking trust in root certificate

  • checking whether the certificates make up a complete certificate chain

• Demo: Firefox: https://www.uni-muenster.de/ | padlock symbol | Show certificates | Details

Thank you

• Rainer Perske

• Westfälische Wilhelms-Universität
  Zentrum für Informationsverarbeitung
  Zertifizierungsstelle
  Röntgenstraße 7-13
  48149 Münster

• ca@uni-muenster.de
  +49 251 83 31590 (fon)
  +49 251 83 31555 (fax)