Symmetric Encryption and Decryption with a key file

Generate a random 256-bit key

To generate a random 256-bit key using /dev/urandom, you can directly extract the random data without the need for additional hashing. Here’s how you can do it:

$ dd if=/dev/urandom of=/path/to/your/keyfile bs=1 count=32

In this command:

if=/dev/urandom specifies the input source as /dev/urandom.

of=/path/to/your/keyfile specifies the output file where your key will be saved.

bs=1 sets the block size to 1 byte.

count=32 specifies that we want 32 bytes (256 bits) of random data.

Example:

$ dd if=/dev/urandom of=symmetric_keyfile.key bs=1 count=32

Encryption

We can use this command to encrypt the sample.txt file:

$ openssl enc -in sample.txt -out sample.txt.enc -e -aes256 -pbkdf2 -kfile symmetric_keyfile.key

Decryption

$ openssl enc -in sample.txt.enc -out sample_decrypted.txt -d -aes256 -pbkdf2  -kfile symmetric_keyfile.key