Author
Bruce Schneier
4 reading cards from 4 books · 1994–2016.
4 cards
Applied Cryptography: Protocols, Algorithms, and Source Code in C · 1994
Modern cryptography protects messages only if the mathematical algorithms are implemented without errors.
Imagine you have a robot that mixes the letters of a letter according to a secret rule. If the rule is good, no one can read the letter without the key. But if the robot makes a small mistake, a clever enemy can guess the rule and read everything. So it is with computer codes.
Secrets and Lies: Digital Security in a Networked World · 2000
Digital security relies on the entire ecosystem, not just passwords and encryption.
Think of a castle with thick walls and a drawbridge. If the bridge is accidentally left down or the guard is asleep, the castle is no longer safe. Similarly, a computer system has many parts: programs, networks, people. If one is weak, everything falls. You must look at everything, not just the lock.
The Process of Security · 2000
The certificate is a photograph, and security is the film it was cut from.
Schneier's sentence is a quarter of a century old and still the best objection to compliance treated as a destination. A certificate says that, on the audit days, a sample of evidence matched the requirements. The system that produced that evidence can be abandoned the next morning and the certificate stays valid until the next surveillance visit. The certificate is a photograph; security is the film it was cut from. Hence the practical test for any compliance programme: if a control only works when an audit approaches, the control does not exist, only audit preparation does. The signs are easy to spot: a year of access reviews all performed in the same week; logs collected retroactively; training completed by everyone in three days. ISO/IEC 27001 is built against exactly this pattern, because it requires measurement (9.1), internal audit (9.2), management review (9.3) and corrective action (10.2). That is cadence, not an event.
“Security is a process, not a product. Products provide some protection, but the only way to effectively do business in an insecure world is to put processes in place that recognize the inherent insecurity in the products.”
Data Is a Toxic Asset, So Why Not Throw It Out? · 2016
Deleting a person is destroying their key, not rewriting history.
Schneier flips the intuition that "data is the new oil": what you do not have cannot be stolen from you, cannot be subpoenaed and does not need an explanation for why you kept it. For the warehouse this becomes a four-stage cycle. Inventory: where the personal-data columns are, marked by classification (direct identifiers, quasi-identifiers, sensitive), discovered automatically where possible. Minimisation: collect only what serves a declared purpose; a full date of birth when you need an age band is a spare column. Retention: every dataset has a deadline and a reason, and deletion is a scheduled job, not a promise. Deletion: provable, including from backups and derived data. This is also where immutability (lesson 10) makes peace with the right to erasure: crypto-shredding. Each person's data is encrypted with their own key; deleting the person means destroying the key. The rows physically remain in the immutable files and in backups, but can never be read by anyone again. A log that cannot be rewritten and a deletion that cannot be undone, at once.
“Data is a toxic asset. We need to start thinking about it as such, and treat it as we would any other source of toxicity.”