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OpenSSL Cookbook  3rd Edition

The definitive guide to using the OpenSSL command line for configuration and testing. Topics covered in this book include key and certificate management, server configuration, a step by step guide to creating a private CA, and testing of online services. Written by Ivan Ristić.


1.2.3 Creating CSRs from Existing Certificates

You can save yourself some typing if you’re renewing a certificate and don’t want to make any changes to the information presented in it. With the following command, you can create a brand-new CSR from an existing certificate:

$ openssl x509 -x509toreq -in fd.crt -out fd.csr -signkey fd.key
🛈︎
Note

Unless you’re using some form of public key pinning and wish to continue using the existing key, it’s best practice to generate a new key every time you apply for a new certificate. Key generation is quick and inexpensive and reduces your exposure in case of a compromise that went undetected.

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