Create, Manage & Convert SSL Certificates with OpenSSL
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.
In this article, I will talk about frequently used OpenSSL commands to help you in the real world.
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
Note: SSL/TLS operation course would be helpful if you are not familiar with the terms.
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.
Create a 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 two years.
openssl req -x509 -sha256 -nodes -days 730 -newkey rsa:2048 -keyout gfselfsigned.key -out gfcert.pem
Verify CSR file
openssl req -noout -text -in geekflare.csr
Verification is essential to ensure you are sending CSR to issuer authority with required details.
Create RSA Private Key
openssl genrsa -out private.key 2048
If you just need to generate RSA private key, you can use the above command. I have included 2048 for stronger encryption.
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 a password, then you can use above openssl rsa -in geekflare.key -check to remove the passphrase key from an existing key.
Verify Private Key
openssl rsa -in certkey.key –check
If you doubt on your key file, you can use the above command to check.
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 an above command which will give you certificate details.
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.
Check Hash Value of A Certificate
openssl x509 -noout -hash -in bestflare.pem
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 then the above command will help you.
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
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 the 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
Create CSR using an 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 an existing one, you can go with the above command.
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. The above command will help you to see the contents of PKCS12 file.
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.
Test SSL certificate of particular URL
openssl s_client -connect yoururl.com:443 –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.
Find out 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.
Check PEM File Certificate Expiration Date
openssl x509 -noout -in certificate.pem -dates
Useful if you are planning to put some 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.
[[email protected] opt]# openssl x509 -noout -in bestflare.pem -dates notBefore=Jul 4 14:02:45 2015 GMT notAfter=Aug 4 09:46:42 2015 GMT [[email protected] opt]#
Check Certificate Expiration Date of SSL URL
openssl s_client -connect secureurl.com:443 2>/dev/null | openssl x509 -noout –enddate
Another useful if you are planning to monitor SSL cert expiration date remotely or particular URL.
[[email protected] opt]# openssl s_client -connect google.com:443 2>/dev/null | openssl x509 -noout -enddate notAfter=Dec 8 00:00:00 2015 GMT
Check if SSL V2 or V3 is accepted on URL
To check SSL V2
openssl s_client -connect secureurl.com:443 -ssl2
To Check SSL V3
openssl s_client -connect secureurl.com:443 –ssl3
To Check TLS 1.0
openssl s_client -connect secureurl.com:443 –tls1
To Check TLS 1.1
openssl s_client -connect secureurl.com:443 –tls1_1
To Check TLS 1.2
openssl s_client -connect secureurl.com:443 –tls1_2
If you are securing web server and need to validate if SSL V2/V3 is enabled or not, you can use the above command. If activated, you will get “CONNECTED” else “handshake failure.”
Verify if the particular cipher is accepted on URL
openssl s_client -cipher 'ECDHE-ECDSA-AES256-SHA' -connect secureurl:443
If you are working on security findings and pen test results show some of the weak ciphers is accepted then to validate, you can use the above command.
Of course, you will have to change the cipher and URL, which you want to test against. If the mentioned cipher is accepted, then you will get “CONNECTED” else “handshake failure.”
I hope above commands help you to know more about OpenSSL to manage SSL certificates for your website.