General OpenSSL Commands

• Generate a new RSA private key

  openssl genrsa 4096 > private.key
  

• Generate a new ECC private key

  #secp256r1
  openssl ecparam -genkey -name secp256r1 | openssl ec -out private.key
  #secp384r1
  openssl ecparam -genkey -name secp384r1 | openssl ec -out private.key
  

• Generate a new private key and Certificate Signing Request

  openssl req -out CSR.csr -new -newkey rsa:2048 -nodes -keyout private.key
  

• Generate a self-signed certificate

  openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -keyout private.key -out certificate.crt
  

• Generate a certificate signing request (CSR) for an existing private key

  openssl req -out CSR.csr -key private.key -new
  

• Generate a multi-domain SSL certificate signing request (CSR) for an existing private key

  openssl req -new -sha256 -key private.key -subj "/" -reqexts SAN -config <(cat /etc/ssl/openssl.cnf <(printf "[SAN]\nsubjectAltName=DNS:yoursite.com,DNS:www.yoursite.com")) > domain.csr
  # if no openssl.cnf
  openssl req -new -sha256 -key private.key -out domain.csr 
  

• Generate a certificate signing request based on an existing certificate

  openssl x509 -x509toreq -in certificate.crt -out CSR.csr -signkey private.key
  

• Remove a passphrase from a private key

  openssl rsa -in private.pem -out newPrivate.pem
  

Checking Using OpenSSL

• Check a Certificate Signing Request (CSR)

  openssl req -text -noout -verify -in CSR.csr
  

• Check a private key

  openssl rsa -in private.key -check
  

• Check a certificate

  openssl x509 -in certificate.crt -text -noout
  

• Check a PKCS#12 file (.pfx or .p12)

  openssl pkcs12 -info -in keyStore.p12
  

• Check the chained certificates

  openssl crl2pkcs7 -nocrl -certfile CHAINED.pem | openssl pkcs7 -print_certs -text -noout
  

Debugging Using OpenSSL

• Check an MD5 hash of the public key to ensure that it matches with what is in a CSR or private key

  openssl x509 -noout -modulus -in certificate.crt | openssl md5
  openssl rsa -noout -modulus -in private.key | openssl md5
  openssl req -noout -modulus -in CSR.csr | openssl md5
  

• Check an SSL connection. All the certificates (including Intermediates) should be displayed

  openssl s_client -connect www.paypal.com:443
  

• Check an SSL connection using specified CA

  openssl s_client -connect  'www.paypal.com:443' -CAfile ca.crt
  

Converting Using OpenSSL

• Convert a DER file (.crt .cer .der) to PEM

  openssl x509 -inform der -in certificate.cer -out certificate.pem
  

• Convert a PEM file to DER

  openssl x509 -outform der -in certificate.pem -out certificate.der
  

• Convert a PKCS#12 file (.pfx .p12) containing a private key and certificates to PEM

  openssl pkcs12 -in keyStore.pfx -out keyStore.pem -nodes
  

• Convert a PEM certificate file and a private key to PKCS#12 (.pfx .p12)

  openssl pkcs12 -export -out certificate.pfx -inkey private.key -in certificate.crt -certfile CACert.crt