Check cert expiry openssl
Print notBefore and notAfter dates
openssl x509 -in cert.pem -noout -dates
more openssl
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Verify cert against CA
openssl verify -CAfile ca.pem cert.pem
Check cert matches key
diff <(openssl x509 -pubkey -noout -in cert.pem) <(openssl pkey -pubout -in key.pem) && echo 'MATCH'
Convert PEM to PKCS#12
openssl pkcs12 -export -in cert.pem -inkey key.pem -certfile ca.pem -out bundle.p12 -name myalias
Extract cert from PKCS#12
openssl pkcs12 -in bundle.p12 -nokeys -out cert.pem && openssl pkcs12 -in bundle.p12 -nocerts -nodes -out key.pem
Check live TLS cert
echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -dates -subject -issuer