RSA encryption guide (short messages <100 characters)

Proof of concept how to secure your messaging with RSA encryption. Using default Mac OS systems console terminal.

Create user A

Generate private key with custom path

openssl genpkey -algorithm RSA -out ~/Desktop/private_key_user_A.pem -pkeyopt rsa_keygen_bits:4096

Generate public key from this private key

openssl rsa -pubout -in ~/Desktop/private_key_user_A.pem -out ~/Desktop/public_key_user_A.pem

To view them

cat private_key_user_A.pem

cat public_key_user_A.pem

Create user B

Generate private key with custom path

openssl genpkey -algorithm RSA -out ~/Desktop/private_key_user_B.pem -pkeyopt rsa_keygen_bits:4096

Generate public key from this private key

openssl rsa -pubout -in ~/Desktop/private_key_user_B.pem -out ~/Desktop/public_key_user_B.pem

To view them

cat private_key_user_B.pem

cat public_key_user_B.pem

Encrypt the message for public key of user B

openssl pkeyutl -encrypt -in ~/Desktop/message.txt -out ~/Desktop/encrypted_message.bin -inkey ~/Desktop/public_key_user_B.pem -pubin

Decrypt the message with private key of user B

openssl pkeyutl -decrypt -in ~/Desktop/encrypted_message.bin -out ~/Desktop/decrypted_message.txt -inkey ~/Desktop/private_key_user_B.pem

RSA+AES encryption guide (large messages >100 characters)

For long text, more than a few words or lines.

Generate AES key

openssl rand -out ~/Desktop/aes_key.bin 32

Encrypt the file using AES key

openssl enc -aes-256-cbc -salt -pbkdf2 -in ~/Desktop/message.txt -out ~/Desktop/encrypted_message.enc -pass file:/Users/admin/Desktop/aes_key.bin

Encrypt AES key with RSA for public key of user B

openssl pkeyutl -encrypt -in ~/Desktop/aes_key.bin -out ~/Desktop/encrypted_aes_key.bin -inkey ~/Desktop/public_key_user_B.pem -pubin

Decrypt AES key with private key of user B

openssl pkeyutl -decrypt -in ~/Desktop/encrypted_aes_key.bin -out ~/Desktop/decrypted_aes_key.bin -inkey ~/Desktop/private_key_user_B.pem

Decrypt the file using AES key

openssl enc -d -aes-256-cbc -pbkdf2 -in ~/Desktop/encrypted_message.enc -out ~/Desktop/decrypted_message.txt -pass file:/Users/admin/Desktop/decrypted_aes_key.bin