Create RSA key using openssl

The following command may be used with OpenSSL to create an RSA encryption key.

Step to create key to encrypt data with RSA algorithm

1. Create private key
2. Use private from (1) to create public key.

---

Generate private key using the following command:

openssl genrsa -out private.pem 4096

In this command, i Have used a key length of 4096 bits. recommended for length is 2048.

This gives you a private key look like:

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

Generate public key from public

The private key from step (1) we can use it to generate public key following.

openssl rsa -in private.pem -puout -out public.pem

This should give you a public key look like:

-----BEGIN PUBLIC KEY-----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-----END PUBLIC KEY-----

Reference:
https://www.scottbrady91.com/openssl/creating-rsa-keys-using-openssl