How to encrypt a file using Blom's scheme?

Question

.NET

They gave the course topic:

Software implementation of the cryptographic information protection system based on the IDEA encryption algorithm in CBC and CFB modes and the key distribution system according to the Blom scheme.

As required, I need to generate a key according to the Blom scheme and encrypt the data with the IDEA algorithm. In this case, the encrypted file should be decrypted without problems on another computer by my program.
I read a lot about Blom's scheme and roughly understood how it works. But I don't understand how I can pass the decryption keys through the encrypted file so that it can be decrypted on any other PC.

Answer 1

To decrypt, the key must already be on the specified PC.
You cannot pass the decryption key along with the file, otherwise anyone can decrypt it.

Answer 2

The shared encryption key can be obtained using the Diffie-Hellman algorithm.
The Diffie-Hellman protocol (eng. Diffie-Hellman, DH) is a cryptographic protocol that allows two or more parties to obtain a shared secret key using a communication channel that is not protected from listening. The resulting key is used to encrypt further exchanges using symmetric encryption algorithms.
Wikipedia to the rescue.