Lecture 7 · 13 October 2025 · Invited lecture
Free Software and Freedom in the Digital Society
An invited lecture by Richard Stallman. It sits outside the chapter structure, has no accompanying slide deck and is not examinable.
Every other page in this companion is written from Venturi's slides. This lecture has no deck, so the page gives only the course context. It does not claim to record or summarize what the speaker said.
Where This Fits
The course is otherwise about mechanism: which constructions provide confidentiality, what a security definition quantifies over and when a protocol can be proved secure. Lecture 7 asks a different question, about the conditions under which these constructions protect the person they are meant to protect.
The connection is direct. Kerckhoffs' principle, introduced in Lecture 1, states that security must rest on the secrecy of the key, while the algorithm itself may be public. The principle is a cryptographic argument for publishing designs. The free software argument extends the same reasoning from the specification to the implementation. A cipher whose design is public but whose implementation cannot be inspected still requires the user to trust someone else's claim about what the code does.
The same point recurs in later chapters. In Chapter 3, the security of TLS (Transport Layer Security) in deployment has repeatedly depended on implementation flaws instead of protocol flaws; in Chapter 6, Bitcoin's trust model is that anyone can run and verify the software. Chapter 8's real/ideal framework (which compares a real protocol run against an idealised, secure-by-design version) proves statements about protocols and leaves the implementing binaries out of scope.
The Free Software Foundation's definition, for reference, grants the user freedom to run the program for any purpose, to study and modify its source, to redistribute copies and to distribute modified versions. Stallman's position is that these freedoms are prerequisites for a user to control their own computing. Without the freedoms, control of the computing passes to whoever wrote the software.
For the Exam
Only material in Venturi's slides is examinable. This lecture has none. It is recorded here for completeness of the course record.