How to Generate a Certificate Signing Request (CSR) With OpenSSL?

Introduction

A Certificate Signing Request (CSR) is a document that contains information about the entity requesting an SSL/TLS certificate. The CSR includes the public key and relevant identifying information about the entity, such as its name and location. This information is used by a certificate authority (CA) to verify that the entity requesting the certificate is who they claim to be.

The CSR is an essential part of the process of obtaining an SSL/TLS certificate because it allows for verification of your identity and ownership of your domain. Without a valid CSR, you cannot obtain an SSL/TLS certificate, which means that your website will not be secured with encryption.

Understanding OpenSSL and Its Components

OpenSSL is an open-source toolkit that provides a secure communications channel between two machines over the internet. It utilizes various cryptographic functions to ensure data confidentiality, integrity, and authenticity. OpenSSL has become one of the most widely used cryptographic libraries in the world, with support for various operating systems including Linux, Windows, and macOS.

Private Key

A private key is a cryptographically secure key that can be used by an individual or entity to sign messages digitally so that they can only be verified by someone who has access to their corresponding public key.

When generating a CSR using OpenSSL, it's important to remember that your private key must remain confidential at all times because if it falls into the wrong hands it could be used for malicious purposes such as impersonation or forgery. To generate a private key using OpenSSL we use this command −

openssl genrsa -out my_private_key.key 2048 

This will create a new file named `my_private_key.key` in our current directory which contains our newly generated private key which we'll later use while generating our CSR.

Public Key

A public key serves as an identifier for your private key allowing others to send you encrypted messages without compromising their privacy since your private key remains confidential at all times. The public-key cryptography underlying SSL/TLS relies on these keys being mathematically related but distinct; it should be computationally infeasible to generate one key from the other.

To generate a public key using OpenSSL we use this command −

openssl rsa -in my_private_key.key -out my_public_key.crt -pubout 

This will create a new file named `my_public_key.crt` in our current directory which contains our newly generated public key. We'll later use this public key while generating our CSR.

Generating a Private Key with OpenSSL

What is a Private Key and Why is it Important?

A private key is a cryptographic key that is used to secure communication between two parties. In the case of SSL/TLS, the private key is used to encrypt data sent from the server to the client. It is important to generate a private key because it allows you to create a secure connection between your server and clients, which is essential in ensuring that sensitive information such as credit card numbers and passwords are kept safe.

Step-by-Step Instructions on How to Generate a Private Key Using OpenSSL

To generate a private key using OpenSSL, follow these simple steps −

• Open up your terminal or command prompt and type in the following command −

openssl genrsa -out example.com.key 2048 

Replace "example.com" with your domain name.

• You will then be prompted to enter a passphrase for your private key.

  This passphrase should be something strong that you can remember easily.

• Once you have entered your passphrase, OpenSSL will generate your private key and save it as "example.com.key" in the current directory.

  It's important to note that once you have generated your private key, you should keep it safe and secure.

Creating a Public Key from the Private Key

Definition of Public Key and Its Importance in Generating CSR

A public key is a cryptographic key that is used to encrypt data and verify digital signatures. It is widely used in web security protocols, such as SSL/TLS, where it helps to establish secure communication between servers and clients.

The CA then uses this public key to create an SSL certificate that can be used for secure communication. The importance of the public key in generating CSR cannot be overstated.

Step-by-Step Instructions on How to Create Public Key from Private Key Using OpenSSL

To create a public key from your private key using OpenSSL, follow these steps −

• Open a terminal window and navigate to the directory where your private key is stored.

• Enter the following command −

openssl rsa -in privkey.pem -pubout -out pubkey.pem 

Replace "privkey.pem" with the name of your private key file and "pubkey.pem" with the name you want to give your newly created public key file.

• Press Enter.

• You will be prompted for your private key passphrase if one was set during generation.

• Once entered successfully, you should see output similar to −

writing RSA key -----BEGIN PUBLIC KEY----- 
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA5mg4yAgzgzY6rS/yz1lx lXTCjLv6NifJ45XQmOt3G+zs2RLpT8coUhU04KNxMm5N+RyOoK7Fw9ud1PvS0yRG 
tCji8bz0Hbszgde4hZl7ogcZffKtWXAkg/TltaiUxrOaEgWJ5jBNs9wAMRqvBR4k 5fetn1Gz/SNSd03LqAFg48mvn67/NA+iQlLOyBbLjMoxoJ2kRSsEnUU6K0AFiXrI 
uPVPYHzDv7qc+eTsqyzKrHG4hg/kVI6xCZNFGX4aWBFEkz50VibLooRv15ymW72y SvqfMY8dZKM033IFDhgx4wjBKCEGD04ehqicI7cP89LCBQr3A+RzfV02riB0UFTs 
DwIDAQAB -----END PUBLIC KEY----- 

This output represents your newly created public key. Congratulations, you have successfully created a public key from your private key using OpenSSL!

Generating a public key from the private key is an essential step in creating a valid certificate signing request when using OpenSSL.

Creating the Certificate Signing Request (CSR)

Definition of CSR and why it's important.

A Certificate Signing Request (CSR) is a digital file that contains information about an organization and the public key that will be included in an SSL/TLS certificate. The CSR is sent to a Certificate Authority (CA) when requesting an SSL/TLS certificate.

The CA will use this information to create a signed certificate, which authenticates the identity of the organization. It's important to generate a CSR because without it, an organization cannot obtain an SSL/TLS certificate.

An SSL/TLS certificate encrypts sensitive data transmitted over the internet between a web server and client browser, providing secure communication.

Step-by-step instructions on how to create the certificate signing request using openssl.

To generate a CSR using OpenSSL, follow these steps −

• Open your Terminal or Command Prompt

• Create a private key −

openssl genpkey -algorithm RSA -out example.com.key

• Enter your details into the CSR:

openssl req -new -key example.com.key -out example.com.csr

• You will be prompted for various details such as Country Name, State or Province Name, Organization Name etc., fill in those fields as required.

• Your CSR has been generated and saved in example.com.csr file.

Be sure to securely store your private key file as well as the generated CSR file since they are both critical components of obtaining your signed SSL/TLS certificates from CAs.

Verifying Your Certificate Signing Request (CSR)

After creating your CSR, it's essential to verify its accuracy to avoid potential errors during the certificate signing process. To verify your CSR, you can use OpenSSL's built-in verification tools.

Firstly, run the following command to check if the CSR matches the private key −

openssl req -noout -modulus -in [csr_file].csr | openssl md5 

Next, run this command to ensure that the information in your CSR is correct −

openssl req -text -in [csr_file].csr 

If everything matches up correctly and there are no errors, you can proceed with submitting your CSR for signing.

Conclusion

Generating a certificate signing request (CSR) with OpenSSL may seem like a daunting task at first; however, it's a critical step in obtaining a signed SSL certificate for your website or application. By following the steps outlined in this article and verifying your CSR's accuracy, you can ensure a smooth process when submitting it to your chosen CA for signing.