One of the most popular commands in SSL to create, convert, manage the SSL Certificates is OpenSSL. There will be many situations where you have to deal with OpenSSL in various ways and here I have listed them for you as a handy cheat sheet.

Some of the abbreviations related to certificates.

  • SSL – Secure Socket Layer
  • CSR – Certificate Signing Request
  • TLS – Transport Layer Security
  • PEM – Privacy Enhanced Mail
  • DER – Distinguished Encoding Rules
  • SHA – Secure Hash Algorithm
  • PKCS – Public-Key Cryptography Standards


1. Create new Private Key and Certificate Signing Request

openssl req -out geekflare.csr -newkey rsa:2048 -nodes -keyout geekflare.key

Above command will generate CSR and 2048-bit RSA key file. If you intend to use this certificate in Apache or Nginx then you need to send this CSR file to certificate issuer authority and they will give you signed certificate mostly in der or pem format which you need to configure in Apache or Nginx web server.

2. Create Self-Signed Certificate

openssl req -x509 -sha256 -nodes -newkey rsa:2048 -keyout gfselfsigned.key -out gfcert.pem

Above command will generate a self-signed certificate and key file with 2048-bit RSA. I have also included sha256 as it’s considered most secure at the moment.

Tip: by default, it will generate self-signed certificate valid for only one month so you may consider defining –days parameter to extend the validity.

Ex: to have self-signed valid for 2 years.

openssl req -x509 -sha256 -nodes -days 730 -newkey rsa:2048 -keyout gfselfsigned.key -out gfcert.pem

3. Verify CSR file

openssl req -noout -text -in geekflare.csr

Verification is important to ensure you are sending CSR to issuer authority with required details.

4. Create RSA Private Key

openssl genrsa -out private.key 2048

If you just need to generate RSA private key, you can use above command. I have included 2048 for stronger encryption.

5. Remove Passphrase from Key

openssl rsa -in certkey.key -out nopassphrase.key

If you are using passphrase in key file and using Apache then every time you start, you have to enter the password. If you are annoyed with entering password then you can use above openssl rsa -in geekflare.key -check to remove the passphrase key from existing key.

6. Verify Private Key

openssl rsa -in certkey.key –check

If you doubt on your key file, you can use above command to check.

7. Verify Certificate File

openssl x509 -in certfile.pem -text –noout

If you would like to validate certificate data like CN, OU, etc then you can use above command which will give you certificate details.

8. Verify the Certificate Signer Authority

openssl x509 -in certfile.pem -noout -issuer -issuer_hash

Certificate issuer authority signs every certificate and in case you need to check them, you can use above command.

9. Check Hash Value of A Certificate

openssl x509 -noout -hash -in bestflare.pem

10. Convert DER to PEM format

openssl x509 –inform der –in sslcert.der –out sslcert.pem

Usually, certificate authority will give you SSL cert in .der format and if you need to use them in apache or .pem format, you can use above command to convert them.

11. Convert PEM to DER format

openssl x509 –outform der –in sslcert.pem –out sslcert.der

In case you need to change .pem format to .der

12. Convert Certificate and Private Key to PKCS#12 format

openssl pkcs12 –export –out sslcert.pfx –inkey key.pem –in sslcert.pem

If you need to use a cert with the java application or with any other who accept only PKCS#12 format, you can use above command, which will generate single pfx containing certificate & key file.

Tip: you can also include chain certificate by passing –chain as below.

openssl pkcs12 –export –out sslcert.pfx –inkey key.pem –in sslcert.pem -chain cacert.pem

13. Create CSR using existing private key

openssl req –out certificate.csr –key existing.key –new

If you don’t want to create a new private key instead using existing one, you can with above command.

14. Check contents of PKCS12 format cert

openssl pkcs12 –info –nodes –in cert.p12

PKCS12 is binary format so you won’t be able to view the content in notepad or another editor. So you got to use above command to view the contents of PKCS12 format file.

15. Convert PKCS12 format to PEM certificate

openssl pkcs12 –in cert.p12 –out cert.pem

If you wish to use existing pkcs12 format with Apache or just in pem format, this will be useful.

16. Test SSL certificate of particular URL

openssl s_client -connect –showcerts

I use this quite often to validate the SSL certificate of particular URL from the server. This is very handy to validate the protocol, cipher, and cert details.

17. Find out OpenSSL version

openssl version

If you are responsible for ensuring OpenSSL is secure then probably one of the first things you got to do is to verify the version.

  1. Check PEM File Certificate Expiration Date
openssl x509 -noout -in certificate.pem -dates

Useful if you are planning to put some kind of monitoring to check the validity. It will show you date in notBefore and notAfter syntax. notAfter is one you will have to verify to confirm if a certificate is expired or still valid.


[root@Chandan opt]# openssl x509 -noout -in bestflare.pem -dates
notBefore=Jul 4 14:02:45 2015 GMT
notAfter=Aug 4 09:46:42 2015 GMT
[root@Chandan opt]#

19. Check Certificate Expiration Date of SSL URL

openssl s_client -connect 2>/dev/null | openssl x509 -noout –enddate

Another useful if you are planning to monitor SSL cert expiration date remotely or particular URL.


[root@Chandan opt]# openssl s_client -connect 2>/dev/null | openssl x509 -noout -enddate

notAfter=Dec 8 00:00:00 2015 GMT

20. Check if SSL V2 or V3 is accepted on URL

To check SSL V2

openssl s_client -connect -ssl2

To Check SSL V3

openssl s_client -connect –ssl3

To Check TLS 1.0

openssl s_client -connect –tls1

To Check TLS 1.1

openssl s_client -connect –tls1_1

To Check TLS 1.2

openssl s_client -connect –tls1_2

If you are securing web server and need to validate if SSL V2/V3 is enabled or not, you can use above command. If enabled, you will get “CONNECTED” else “handshake failure

21. Verify if particular cipher is accepted on URL

openssl s_client -cipher ‘ECDHE-ECDSA-AES256-SHA’ -connect secureurl:443

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

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

You can add -nocerts to only output the private key or add -nokeys to only output the certificates.

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

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