Computer Networks · free preview
Cryptographic Building Blocks
Security on a network rests on a few cryptographic primitives, ciphers parameterized by keys so that algorithms can be public and only keys secret, secret-key block ciphers like DES and its successors scrambling fixed-size blocks fast, public-key ciphers like RSA splitting the key into a public half anyone can use and a private half only the owner holds, which buys both secrecy and authentication depending on the direction of use but runs too slowly for bulk data, and authenticators built from collision-resistant hashes, message authentication codes keyed by shared secrets, and digital signatures, a hash encrypted with a private key, which alone provide nonrepudiation because only the owner could have produced them.
1. Keys, Not Algorithms
Keys, Not Algorithms
2. From Blocks to Messages
From Blocks to Messages
3. Two Halves of One Key
Two Halves of One Key
4. Proving Integrity
Proving Integrity
5. The public algorithm
Why are cipher algorithms published rather than kept secret?
6. Repairing DES
Why does 3DES encrypt with key1, decrypt with key2, and encrypt with key3 rather than encrypting three times?
7. Two directions, two properties
What does encrypting with a private key achieve, given that anyone can decrypt with the public key?
8. The birthday shortcut
Why does a 128-bit digest offer only about 64 bits of collision resistance?
9. The third party
Why can a digital signature convince a judge while a MAC cannot?
10. The hybrid pattern
How do real systems combine public-key and secret-key ciphers?
11. The secret half
In a public-key cipher, which half of the key pair never leaves its owner?
12. The fixed-size fingerprint
What is the fixed-size output of a cryptographic hash function called?
13. The keyed digest
What do you get when a shared secret key is folded into a message digest so only key holders can produce it?
14. The undeniable proof
What authenticator is made by encrypting a digest with the sender's private key, providing nonrepudiation?
Practice this interactively
Free account · instant grading · spaced review that schedules itself.
Start this course for free