Openssl

openssl command

certificate

openssl s_client -connect mars.merhot.dk:443 -verify_return_error -verify_hostname mars.merhot.dk -trace

Debug

Example when debugging a tls connection to mosquitto MQTT broker.

root@beaglebone:/home/debian# openssl s_client -connect 127.0.0.1:8883
CONNECTED(00000003)
Can't use SSL_get_servername
depth=0 C = DK, ST = Denmark, L = Viborg, O = Mercantec, CN = beaglebone.localdomain, emailAddress = heth@mercantec.dk
verify error:num=18:self signed certificate
.....

Where did it go wrong - see only SSL negotiation

root@beaglebone:/home/debian/certs/ca# openssl s_client -state -nbio -connect 127.0.0.1:8883 | grep "^SSL"
SSL_connect:before SSL initialization
SSL_connect:SSLv3/TLS write client hello
SSL_connect:error in SSLv3/TLS write client hello
...
3069829136:error:1409445C:SSL routines:ssl3_read_bytes:tlsv13 alert certificate required:../ssl/record/rec_layer_s3.c:1544:SSL alert number 116

On Mosquitto brokerside:

root@beaglebone:/home/debian# /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf -v
1621664904: mosquitto version 2.0.7 starting
1621664904: Config loaded from /etc/mosquitto/mosquitto.conf.
1621664904: Opening ipv4 listen socket on port 1883.
1621664904: Opening ipv6 listen socket on port 1883.
1621664904: Opening ipv4 listen socket on port 8883.
1621664904: Opening ipv6 listen socket on port 8883.
1621664904: mosquitto version 2.0.7 running
1621664907: New connection from 127.0.0.1:45026 on port 1883.
1621664907: Sending CONNACK to 127.0.0.1 (0, 5)
1621664907: Client <unknown> disconnected, not authorised.
1621665067: New connection from 127.0.0.1:54532 on port 8883.
1621665067: OpenSSL Error[0]: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca

Error 14094418 - alert unknown ca

openssl errornumber to errorstring: (Just nice to know)

root@beaglebone:/home/debian/certs/ca# openssl errstr 14094418
error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca

Checking SSL server TLS version and capabilities

root@beaglebone:/home/debian/certs/ca# nmap --script ssl-enum-ciphers -p 8883 127.0.0.1
Starting Nmap 7.70 ( https://nmap.org ) at 2021-05-22 08:27 UTC
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00037s latency).

PORT     STATE SERVICE
8883/tcp open  secure-mqtt
| ssl-enum-ciphers:
|   TLSv1.2:
|     ciphers:
|       TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (ecdh_x25519) - A
|       TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (dh 2048) - A
|       TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 (ecdh_x25519) - A
...

Nmap done: 1 IP address (1 host up) scanned in 5.77 seconds

Links

• See certutil Windows