Can I send an encoded letter to an inmate?

I have some details pertaining to business that I wish to discuss with my friend who is in jail. I’d prefer the jail does not read the messages. We both know the Diffie-Hellman exponential key exchange protocol so my plan was to send him my DH parameters with the enciphered message and he would simply XOR the message after obtaining the key with my parameters and his. The underlying encryption is similar to the concept of the one time pad and it is easy enough to implement on paper. Diffie-Hellman is extremely strong.

If I send an encrypted message to jail will it be rejected? I see nothing in the rules about encryption