Do federal prisoners retain their First Amendment rights?
As with most issues, the technically legal answer may vary from the practical one. Generally, the Bureau of Prisons encourages prisoners to read and write and create written works during their sentences. There are few restrictions, other than those that threaten the safety and security of the institution itself. However, public blog posts or articles that are critical of the BOP may lead to retaliation within the system.
For an excellent discussion of the issue, click HERE.