CSR + key in one shot

Generate key+CSR with SAN inline; -addext avoids editing openssl.cnf

openssl req -new -newkey rsa:2048 -nodes -keyout key.pem -out req.csr -subj "/CN=<host>" -addext "subjectAltName=DNS:<host>"
tool
openssl27 commands
tags
openssltlssecurity

More openssl commands

  • Self-signed cert with SAN
    openssl req -x509 -newkey rsa:2048 -nodes -keyout key.pem -out cert.pem -days 365 -subj "/CN=<host>" -addext "subjectAltName=DNS:<host>"

    One-liner self-signed cert valid 1y; SAN required or TLS clients reject it

  • PEM to PKCS12 bundle
    openssl pkcs12 -export -in cert.pem -inkey key.pem -certfile ca-chain.pem -out bundle.p12 -name <name>

    Bundle cert+key+chain into .p12 for Java keystores / Windows imports

  • STARTTLS protocol probe
    openssl s_client -connect <host>:5432 -starttls postgres -showcerts </dev/null 2>/dev/null

    Inspect TLS on STARTTLS services; swap postgres for smtp/imap/mysql/ldap

  • Generate Ed25519 key
    openssl genpkey -algorithm ed25519 -out ed25519.pem

    Modern: Ed25519 keys are tiny and fast vs RSA; use for signing/mTLS

  • Test specific TLS protocol
    openssl s_client -connect <host>:443 -tls1_2 </dev/null 2>&1 | grep -E 'Protocol|Cipher'

    Force a version to confirm support; use -tls1_3 / -no_tls1_2 to test policy

all 27 openssl commands