How it works
Encryption protects readable data by making it unreadable without a key. Hashing supports integrity checks and password storage patterns. TLS protects data in transit.
Use encryption for sensitive data in transit and at rest when appropriate; use hashing when you need to verify without revealing the original value.
Common error
Encoding, compression, hashing, and encryption are not interchangeable.
Worked example
Choose a cryptographic mechanism based on the required property.
Evidence
Goal A: private transfer
Goal B: compare a downloaded file with a trusted digest
Goal C: recover readable stored data with a keyUse suitable encrypted transport for A, a cryptographic hash comparison with a trusted expected digest for B, and encryption with controlled key access for C. A matching digest from an untrusted source does not establish authenticity. Hashing is not reversible encryption.
Exercises
5.3.1
Can Base64 encoding protect a secret from a person who receives the encoded text? Explain.
Show solution
No. Base64 is a reversible representation format without a secret key. Confidentiality needs an appropriate encryption and access-control design.
5.3.2
Why is a salted, deliberately slow password-hashing scheme preferable to storing plaintext passwords?
Show solution
It avoids directly exposing readable passwords in the stored record and raises the cost of guessing against a stolen database. It still needs secure authentication, access controls, and operational protection.