Openssl, s_client

Retrieve and parse certificate from server

$ echo | openssl s_client -connect servername:443 \
| openssl x509 -noout -text
 openssl s_client -CAfile ./CAcert.pem -connect servername:1636 -ssl3
 openssl s_client -connect servername:1636 -cert clientcert.cer -certform DER -key clientkey.key

Parse an ASN.1 sequence.

$ openssl asn1parse -inform DER -in sample.cer -dump