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I am setting up an IKEv2 VPN server using strongSwan on Ubuntu and experiencing issues with client authentication due to CA certificate errors.

This is the base: https://www.digitalocean.com/community/tutorials/how-to-set-up-an-ikev2-vpn-server-with-strongswan-on-ubuntu-20-04

My setup is as follows:

VPN Server: Ubuntu 24 LTS with strongSwan 6.6 Certificate Details: Subject: CN = vpn.mydomain.com Subject Alternative Name (SAN): DNS:vpn.mydomain.com, DNS:www. vpn.mydomain.com The server's SSL certificate is correctly configured with its SAN covering both vpn.mydomain.com and www.vpn.mydomain.com. However, when client ( Android 14 Pixel 7A ) attempt to connect, the connection fails with the error: failed to establish vpn verifying server authentication failed

User authentication : EAP

It seems like the issue is with the CA certificate not being recognized or not being available on the client devices, despite the server certificate appearing to be properly set up and linked to its issuer.

Client log on android strongSwan client show:

May  2 14:20:13 12[IKE] received end entity cert "CN=vpn.mydomain.com"
May  2 14:20:13 12[CFG]   using certificate "CN=vpn.mydomain.com"
May  2 14:20:13 12[CFG] no issuer certificate found for "CN=vpn.mydomain.com"
May  2 14:20:13 12[CFG]   issuer is "C=LV, L=Riga, O=GoGetSSL, CN=GoGetSSL RSA DV CA"
May  2 14:20:13 12[IKE] **no trusted RSA public key found for **'vpn.mydomain.com'
May  2 14:20:13 12[ENC] generating INFORMATIONAL request 2 [ N(AUTH_FAILED) ]

My server certificate: I got this certificate on GoGetSSL website. My idea here not using self-signed certificates, so that I don't need to install root certificate on any device. GoGetSSL is USERTrust RSA certification Authority and it exist on my device. So my server certificate should be trust. And yeah my domain is not vpn.mydomain.com, it is just example. I tried also Lets encrypt, result the same. But on my MacOs and iPhone all work perfectly fine.

ertificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            83:fc:58:44:59:f9:27:63:12:a2:23:57:5f:df:7a:54
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: C = LV, L = Riga, O = GoGetSSL, CN = GoGetSSL RSA DV CA
        Validity
            Not Before: May  2 00:00:00 2024 GMT
            Not After : Jul 31 23:59:59 2024 GMT
        Subject: CN = **vpn.mydomain.com**
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:97:d8:74:fb:66:a9:e8:95:61:91:8b:50:85:c5:
                    04:23:c0:09:0a:d6:ad:a5:0e:71:e5:76:69:c9:3a:
                    59:96:31:1f:7c:2f:ea:a1:27:14:6e:49:f2:f3:53:
                    af:e1:d3:1a:da:8c:d3:7e:53:ba:49:8f:50:bf:6f:
                    a7:1a:1b:1c:ce:c3:a7:9a:2d:71:cd:df:de:03:13:
                    23:53:04:6c:72:cb:69:8c:14:d9:63:40:5b:38:ca:
                    e9:b2:3a:bf:88:a6:39:fa:fe:03:85:2f:37:a8:7d:
                    c1:1c:ba:4d:69:ee:e1:bb:b1:49:71:d1:d7:4f:2c:
                    94:8a:91:39:6e:e7:41:b8:9d:f8:45:65:7c:93:c3:
                    45:4b:92:39:a5:25:d9:a4:8a:5f:33:37:85:c6:56:
                    83:a0:a9:c3:09:3d:5b:fd:2d:17:d3:94:25:2a:c2:
                    6e:71:aa:21:8c:25:91:be:ec:30:7f:b4:da:3d:43:
                    9c:1c:53:b9:55:45:dc:b9:97:e3:4c:c0:a6:9a:c9:
                    f0:42:67:14:dc:5d:c4:b8:3a:eb:8b:17:c5:92:f3:
                    1c:5d:7e:be:5e:e1:74:9f:f6:63:8c:06:b2:a6:08:
                    02:b3:d5:75:97:d9:63:01:e2:13:6d:5f:52:f9:0b:
                    9d:36:2e:ef:1b:59:3f:b5:bd:a6:f6:0c:5d:cc:fd:
                    f2:d3
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Authority Key Identifier: 
                F9:FB:50:C4:8B:67:BB:67:64:FE:83:21:A6:A9:CE:3F:55:84:93:99
            X509v3 Subject Key Identifier: 
                C5:D5:1A:C2:81:B3:84:11:B3:90:4E:FC:1E:11:B1:5B:9C:DF:A1:61
            X509v3 Key Usage: critical
                Digital Signature, Key Encipherment
            X509v3 Basic Constraints: critical
                CA:FALSE
            X509v3 Extended Key Usage: 
                TLS Web Server Authentication, TLS Web Client Authentication
            X509v3 Certificate Policies: 
                Policy: 1.3.6.1.4.1.6449.1.2.2.64
                  CPS: https://cps.usertrust.com
                Policy: 2.23.140.1.2.1
            X509v3 CRL Distribution Points: 
                Full Name:
                  URI:http://crl.usertrust.com/GoGetSSLRSADVCA.crl
            Authority Information Access: 
                CA Issuers - URI:http://crt.usertrust.com/GoGetSSLRSADVCA.crt
                OCSP - URI:http://ocsp.usertrust.com
            X509v3 Subject Alternative Name: 
                DNS:vpn.mydomain.com, DNS:www.vpn.mydomain.com
            CT Precertificate SCTs: 
                Signed Certificate Timestamp:
                    Version   : v1 (0x0)
                    Log ID    : 76:FF:88:3F:0A:B6:FB:95:51:C2:61:CC:F5:87:BA:34:
                                B4:A4:CD:BB:29:DC:68:42:0A:9F:E6:67:4C:5A:3A:74
                    Timestamp : May  2 20:33:32.442 2024 GMT
                    Extensions: none
                    Signature : ecdsa-with-SHA256
                                30:45:02:21:00:97:26:B7:25:08:D3:C8:02:91:40:5D:
                                B8:80:7A:99:0D:E9:94:A7:10:C6:B9:AC:00:C0:F8:39:
                                E2:D3:74:50:A3:02:20:10:42:A4:0A:03:EF:A6:38:3D:
                                65:09:98:ED:72:0D:C0:AD:F8:EB:61:AD:4E:DB:A5:4C:
                                CE:30:7D:78:0D:15:85
                Signed Certificate Timestamp:
                    Version   : v1 (0x0)
                    Log ID    : 3F:17:4B:4F:D7:22:47:58:94:1D:65:1C:84:BE:0D:12:
                                ED:90:37:7F:1F:85:6A:EB:C1:BF:28:85:EC:F8:64:6E
                    Timestamp : May  2 20:33:32.415 2024 GMT
                    Extensions: none
                    Signature : ecdsa-with-SHA256
                                30:46:02:21:00:A4:51:BD:EE:AF:51:4A:88:37:9A:2E:
                                BA:E4:08:36:49:2A:55:3E:39:C5:FB:1C:21:2D:9D:30:
                                5C:F5:BD:AE:58:02:21:00:BE:D3:A0:6A:06:4D:B9:0C:
                                9E:48:7D:8F:FF:93:3E:EB:4C:CF:F9:57:00:D2:84:41:
                                D1:43:BB:F2:F5:8A:3A:13
    Signature Algorithm: sha256WithRSAEncryption
    Signature Value:
        14:36:32:d4:9b:b3:d4:ab:9e:ed:87:e5:5e:28:aa:e7:5d:15:
        56:eb:ca:f7:b0:ca:09:d9:2b:af:35:92:38:0f:c6:f9:89:c7:
        85:36:63:28:a4:c7:10:f9:02:23:76:0e:cb:78:80:08:1b:3c:
        74:ec:b2:98:92:e9:a2:80:52:98:7d:95:36:ac:28:a3:01:62:
        ba:08:f6:8d:d4:ac:18:51:7c:20:31:03:22:ff:76:69:10:65:
        8e:ba:5f:4b:86:12:69:21:2a:78:41:f4:7b:cd:89:af:48:2c:
        09:40:a7:8f:c6:5e:1e:ee:a9:26:2e:61:c6:65:3a:aa:67:de:
        6c:15:93:d6:6d:09:0a:35:72:2c:81:88:aa:38:99:72:bb:1e:
        5d:ae:1f:78:6a:7d:1a:3b:4d:03:8b:12:af:c2:4e:13:14:42:
        0a:d5:6d:20:39:fd:1c:70:47:6f:39:19:35:a3:1a:35:d3:25:
        d0:3f:81:9b:a7:e9:48:98:76:51:6f:f7:1b:90:20:0c:61:e8:
        0c:bc:7d:d9:66:06:6a:5c:a3:1b:c6:ad:6d:20:02:f0:d6:1e:
        9e:03:4c:40:71:81:ec:d3:db:57:33:ec:71:34:53:4d:6c:9e:
        9f:61:bc:72:2f:59:4e:bd:27:0b:cd:2d:f2:5e:30:a1:8c:5b:
        8f:3c:c0:99

Here is my config

config setup
    charondebug="ike 1, knl 1, cfg 0"
    uniqueids=no


conn ikev2-vpn
    auto=add
    compress=no
    type=tunnel
    keyexchange=ikev2
    fragmentation=yes
    forceencaps=yes
    dpdaction=clear
    dpddelay=300s
    rekey=no
    left=%any
    [email protected]
    leftcert=dinochain.pem
    
    leftsendcert=always
    leftsubnet=0.0.0.0/0
    right=%any
    rightid=%any
   
    rightauth=eap-mschapv2
    rightsourceip=10.10.10.0/24
    rightdns=8.8.8.8,8.8.4.4
    rightsendcert=never
    eap_identity=%identity

    ike=aes128-sha1-modp1024,aes128-sha1-modp1536,aes128-sha1-modp2048,aes128-sha256-ecp256,aes128-sha256-modp1024,aes128-sha256-modp1536,aes128-sha256-modp2048,aes256-aes128-sha25>
    esp=aes128-aes256-sha1-sha256-modp2048-modp4096-modp1024,aes128-sha1,aes128-sha1-modp1024,aes128-sha1-modp1536,aes128-sha1-modp2048,aes128-sha256,aes128-sha256-ecp256,aes128-sh>

and secrets

: RSA dinopriv.pem
user : EAP "password"

Here are my questions:

How can I ensure that the CA certificate is properly installed or recognized on client devices? Is there a specific configuration step I might be missing on the server side that could resolve this authentication issue?

Any help or suggestions would be greatly appreciated as I am currently unable to get the VPN connection established due to this server authentication error.

I tried Lets Encrypt and then tried GOGETSSL. I can't find Lets Encrypt in my system certificates on android. But GOGETSSL exists. But it never helps.

Improve this question
8
  • For either CA, you have to make sure the intermediate CA certificate that issued the server certificate is also sent. So install it in /etc/ipsec.d/cacerts.
    – ecdsa
    Commented May 3 at 10:08
  • I have 4 different files. Which one is intermediate? AAA_Certificate_Services.crt GoGetSSL_RSA_DV_CA.crt USERTrust_RSA_Certification_Authority.crt vpn_mydomain_com.crt (this one is main server certificate I believe ) and second question, ...install it in /etc/ipsec.d/cacerts.. it means just CP this files in this folder? as I see here wiki.strongswan.org/projects/strongswan/wiki/CaSection "Because the daemon automatically imports CA certificates from /etc/ipsec.d/cacerts, there is no need to explicitly add them with a CA section" it should work automatically .
    – splagov
    Commented May 3 at 11:12
  • Juts tested! Hell it works. Just put this file gogetssl_rsa_dv_ca.crt and android+windows worked. But here next question, how in case of LetsEncrypt? Looks like there is no intermediate certificates. I have just 2 files 'fullchain.pem' and 'privkey.pem'
    – splagov
    Commented May 3 at 11:26
  • Tested. certbot creates 'fullchain.pem' and 'privkey.pem'. then I need to create anyname.crt here /etc/ipsec.d/cacerts Put in the second certificate from fullchain.pem file. Now jut need to create some logic, to copy this part of certificate automatically when certbot update the certificate. But yeah. Question solved. Thanks for helping.
    – splagov
    Commented May 3 at 12:18
  • Don't use fullchain.pem use chain.pem that contains the intermediate CA certificate first and that's all you need on the server.
    – ecdsa
    Commented May 3 at 12:24

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This is the answer!

For either CA, you have to make sure the intermediate CA certificate that issued the server certificate is also sent. So install it in

/etc/ipsec.d/cacerts
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