Generating Certificates

Generate host, user, and server certificates for VPN authentication.

End-entity certificates identify VPN gateways and clients during IKEv2 authentication. Each certificate is signed by the CA and bound to a specific distinguished name and optional Subject Alternative Names (SANs).

1. Generate the host private key

   Create a private key for the host or user. Ed25519 is recommended:

   pki --gen --type ed25519 --outform pem > moonKey.pem
   

   Alternatively, generate a 3072-bit RSA key in binary DER format:

   pki --gen --type rsa --size 3072 > moonKey.der
   

   A TPM 2.0 Trusted Platform Module can store RSA or ECDSA keys in hardware, protecting them from extraction even if the OS is compromised. See the TPM 2.0 HOWTO for details.

2. Create a certificate signing request

   Generate a PKCS#10 CSR containing the subject DN and SANs:

   pki --req --type priv \
       --in moonKey.pem \
       --dn "C=CH, O=strongSwan, CN=moon.strongswan.org" \
       --san moon.strongswan.org \
       --outform pem > moonReq.pem
   

   The --san option can be repeated to add multiple Subject Alternative Names. The value type is inferred automatically:

   --san moon.strongswan.org     # Fully qualified hostname
   --san [e-mail]    # RFC 822 email address
   --san 192.168.0.1             # IPv4 address
   --san fec0::1                 # IPv6 address
   

   Many IKEv2 implementations match peer identity against the SAN, not the CN. Always include the intended identity as a SAN.

3. Issue the signed certificate

   Have the CA sign the CSR and produce an end-entity certificate:

   pki --issue \
       --cacert strongswanCert.pem --cakey strongswanKey.pem \
       --type pkcs10 --in moonReq.pem \
       --serial 01 --lifetime 1826 \
       --outform pem > moonCert.pem
   

   Key options:

   Option	Description
   --cacert	CA certificate file
   --cakey	CA private key file
   --type pkcs10	Input is a PKCS#10 CSR (use pub or priv for raw key input)
   --serial <hex>	Hexadecimal serial number; random if omitted
   --lifetime <days>	Certificate validity in days (1826 = 5 years)

   Adding the TLS server authentication Extended Key Usage (EKU) — required by Windows, iOS, and macOS VPN clients for gateway certificates:

   pki --issue ... --flag serverAuth
   

   Available --flag values: serverAuth, clientAuth, ikeIntermediate, crlSign, ocspSigning, msSmartcardLogon.

   Adding CRL distribution points so peers can fetch revocation status dynamically:

   pki --issue ... --crl http://crl.strongswan.org/strongswan.crl
   pki --issue ... --crl "ldap://ldap.strongswan.org/cn=strongSwan Root CA,o=strongSwan,c=CH?certificateRevocationList"
   
4. Inspect the issued certificate

   Verify the certificate content before deploying it:

   pki --print --in moonCert.pem
   

   Expected output:

   subject:  "C=CH, O=strongSwan, CN=moon.strongswan.org"
   issuer:   "C=CH, O=strongSwan, CN=strongSwan Root CA"
   validity:  not before May 19 10:28:19 2017, ok
              not after  May 19 10:28:19 2022, ok (expires in 1825 days)
   serial:    01
   altNames:  moon.strongswan.org
   flags:     serverAuth
   CRL URIs:  http://crl.strongswan.org/strongswan.crl
   authkeyId: 2b:95:14:5b:c3:22:87:de:d1:42:91:88:63:b3:d5:c1:92:7a:0f:5d
   subjkeyId: 60:9d:de:30:a6:ca:b9:8e:87:bb:33:23:61:19:18:b8:c4:7e:23:8f
   pubkey:    ED25519 256 bits
   keyid:     39:1b:b3:c2:34:72:1a:01:08:40:ce:97:75:b8:be:ce:24:30:26:29
   subjkey:   60:9d:de:30:a6:ca:b9:8e:87:bb:33:23:61:19:18:b8:c4:7e:23:8f
   

   Confirm that authkeyId matches the CA’s subjkeyId, that the SAN is present, and that any required EKU flags appear.

5. Install credentials on the host

   Place files in the correct swanctl directories:

   install -m 644 strongswanCert.pem /etc/swanctl/x509ca/
   install -m 644 moonCert.pem       /etc/swanctl/x509/
   install -m 600 moonKey.pem        /etc/swanctl/private/
   

   Reload credentials into the running daemon:

   swanctl --load-creds
   

Creating a PKCS#12 bundle for clients

Windows, macOS, Android, and iOS clients typically import credentials as a single PKCS#12 (.p12) file. The pki tool does not create PKCS#12 files directly; use openssl instead:

openssl pkcs12 -export \
    -inkey carolKey.pem \
    -in carolCert.pem -name "carol" \
    -certfile strongswanCert.pem -caname "strongSwan Root CA" \
    -out carolCert.p12

The resulting carolCert.p12 contains the user’s private key, certificate, and the CA certificate in a single password-protected file.

The export password protects the private key inside the bundle. Use a strong password and transmit the .p12 file over a secure channel (not plain email).

Credential file locations summary

File	Directory	Mode
CA certificate	/etc/swanctl/x509ca/	644
Host / user certificate	/etc/swanctl/x509/	644
Private key	/etc/swanctl/private/	600
PKCS#12 bundle	/etc/swanctl/pkcs12/	600