How do I generate the certificates for EAP-TLS Wi-Fi?

Question

I want to connect a Linux machine to WPA2 Enterprise Wi-Fi (that I manage). The certificates I created with OpenSSL work well with Android and iOS devices, but I can't figure out what types of certificates are expected by wpa_supplicant.

Basically, I have a ca.pem, and, for a given device, the following files are being generated:

demo.crt
demo.csr
demo.key
demo.p12

It looks like wpa_supplicant can work with either a file containing both the public and the private certificate, as well as two files. Originally, I was using two files:

demo.key
demo.pem, created by running openssl pkcs12 -in demo.p12 -out demo.pem -clcerts.

wpa_supplicant.conf was configured like this:

network={
    ssid="HelloWorld"
    key_mgmt=WPA-EAP
    pairwise=CCMP
    group=CCMP
    eap=TLS
    identity="[email protected]"
    ca_cert="/etc/ssl/private/ca.pem"
    client_cert="/etc/ssl/private/demo.pem"
    private_key="/etc/ssl/private/demo.key"
    private_key_passwd=...
}

The authentication fails with the following error:

OpenSSL: tls_read_pkcs12 - Failed to use PKCS#12 file error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag

If I remove client_cert and use only private_key, pointing to the .pem file, the error is still the same.

If I point it to .p12, the error is:

OpenSSL: tls_connection_private_key - Failed to load private key error:00000000:lib(0):func(0):reason(0)

Debian's documentation tells that the PEM should be created from a .pfx. When I do that:

openssl pkcs12 -export -out demo.pfx -inkey demo.key -in demo.crt -certfile ca.crt
openssl pkcs12 -in demo.pfx -out demo.pem -clcerts

the original error is back:

OpenSSL: tls_read_pkcs12 - Failed to use PKCS#12 file error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag

How exactly should I generate the certificates for wpa_supplicant?

If you are creating your certificates on the windows side, either this is not the right group to ask or the question is not correctly framed. — Rui F Ribeiro, Apr 28 '20 at 01:15
@RuiFRibeiro: Windows side? The certificates are generated on a Linux machine. Although I'm not sure how this is relevant: I suppose that OpenSSL generates the same certificates independently of the operating system. — Arseni Mourzenko, Apr 28 '20 at 14:13
Ah. Debian docs does not say you need .pfx, hence the confusion. It says it needs PEM, no matter what format it is received. For EAP-TTLS, client certificates are not mandatory. (and Windows use their own tools) — Rui F Ribeiro, Apr 28 '20 at 17:16
@RuiFRibeiro: I see. Sorry, my question is indeed not easily readable, but I can't figure out how can I make it more readable without removing necessary details. Essentially, the question itself is in the title. The details are here to avoid answers which barely tell what I already know/have tried, such as “Simply use .p12 and it will work”—no, it won't. — Arseni Mourzenko, Apr 28 '20 at 21:26
Are you authenticating users via certificate or is just the server certificate? Or both? Are Windows or mobile clients authenticating? — Rui F Ribeiro, Apr 29 '20 at 11:06
@RuiFRibeiro: each *device* (rather than a user) has its own certificate (`demo.pem` in my question). Among the clients, there are two Android devices and an iOS device; all three use their own client certificates and have no issues authenticating. The RADIUS server has, obviously, its own certificate. — Arseni Mourzenko, Apr 29 '20 at 17:18
in my experience iOS devices are much more finicky with web/RADIUS certificates than Linux. — Rui F Ribeiro, Apr 29 '20 at 19:29

Rui F Ribeiro · Accepted Answer · 2020-04-30T19:12:15.693

In your wpa_supplicant.conf file, it should be eap=TTLS

As in:

network={
ssid="HelloWorld"
key_mgmt=WPA-EAP
pairwise=CCMP
group=CCMP
eap=TTLS
identity="[email protected]"
ca_cert="/etc/ssl/private/ca.pem"
client_cert="/etc/ssl/private/demo.pem"
private_key="/etc/ssl/private/demo.key"
private_key_passwd=...
}

Also, depending on the configuration, you might need anonymous_identity and phase2.

Supposing it is EAP-TTLS-MSChapv2:

network={
ssid="HelloWorld"
key_mgmt=WPA-EAP
pairwise=CCMP
group=CCMP
eap=TTLS
identity="[email protected]"
ca_cert="/etc/ssl/private/ca.pem"
client_cert="/etc/ssl/private/demo.pem"
private_key="/etc/ssl/private/demo.key"
private_key_passwd=...
phase2="auth=MSCHAPV2"
}

The question was about EAP-TLS, but the answer is for EAP-TTLS-MSCHAPv2. As long as this is your private AP you could just change the authentication protocol. In the general case you cannot. — Uwe Geuder, Jun 25 '21 at 11:17

How do I generate the certificates for EAP-TLS Wi-Fi?

1 Answers1