Openssl by Example

Table of contents

• Symmetric key
  • Encryption
  • Decryption
• Asymmetric key
  • Key Generation
    • Public key
    • Private key
  • Encryption
  • Decryption
  • Sending signed messages
  • Reading signed messages
  • Encrypting private key
• Others
  • Find openssl version
  • List ciphers

Symmetric key

Encryption

$ echo "top secret text" | openssl enc -aes-256-cbc -base64
enter aes-256-cbc encryption password:
Verifying - enter aes-256-cbc encryption password:
<< encrypted text >>

Decryption

$ echo "<< encrypted text >>" | openssl enc -d -aes-256-cbc -base64
enter aes-256-cbc decryption password:
top secret text

Asymmetric key

Key Generation

Public key

openssl genrsa -out private.pem 2048

Private key

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

Encryption

openssl rsautl -encrypt -in secret-transmission.txt -out secret-transmission.txt.enc -inkey public.pem -pubin

Decryption

openssl rsautl -decrypt -in secret-transmission.txt.enc -out secret-transmission.txt -inkey private.pem

Sending signed messages

openssl rsautl -sign -in secret-transmission.txt -out secret-transmission.txt.enc.signed -inkey private.pem

Reading signed messages

openssl rsautl -verify -in secret-transmission.txt.enc.signed -out secret-transmission.txt -inkey public.pem -pubin

Encrypting private key

Never store private key in clear text format!

openssl rsa -in private.pem -des3 -out private-enc.pem

Others

Find openssl version

$ openssl version
LibreSSL 2.6.4

List ciphers

openssl list-cipher-commands