How feasible is to brute force the ENCRYPTION key if you have
- the clear-text message
- the encrypted-version of the same message
- you know that Rijandel is the encryption algorithm
- you know that the salt is 2 bytes long
How feasible is to brute force the ENCRYPTION key if you have
The attack you describe is called a "known-plaintext attack". It was commonly used to break older encryption schemes, most notably Enigma in the second world war.
AES/Rijndael is not susceptible to known-plaintext attacks.
Further reading: