How to encrypt a file with an RSA public key using OpenSSL "rsautl" command?

If you want to encrypt a file with an RSA public in order to send private message to the owner of the public key, you can use the OpenSSL "rsault -encrypt" command as shown below:

C:\Users\fyicenter>type clear.txt
The quick brown fox jumped over the lazy dog.

C:\Users\fyicenter>\local\openssl\openssl.exe
OpenSSL> rsautl -encrypt -pubin -inkey my_rsa_pub.key -in clear.txt 
   -out cipher.txt
OpenSSL> exit

C:\Users\fyicenter>dir *.txt
   128 cipher.txt
    45 clear.txt

Options used in the "rsautl" command are:

• "-encrypt" - Encrypt the input data with RSA keys.
• "-pubin" - Use RSA public key.
• "-inkey my_rsa_pub.key" - Read RSA key, the public key, from the given file.
• "-in clear.txt" - Read input data, the clear text, from the given file.
• "-out cipher.txt" - Save output data, the cipher text, to the given file.

Note that the encrypted data, cipher.txt, can only be decrypted by the owner of the public key with his/her matching private key.

⇒OpenSSL "rsautl" Command for RSA Keys

⇒⇒OpenSSL Tutorials