2023-08-23 17:09:04 +00:00
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# Real World Crypto 101
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My notes when reading
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[Real-World Cryptography](https://www.manning.com/books/real-world-cryptography)
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**Hash** function convert from input to digest:
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- Pre-image resistance: Given digest, can not find input
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- Second pre-image resistance: Given input, digest, can not find another input
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produce same digest. Small change to input make digest big change.
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- Collision resistance: Can not find 2 input produce same digest.
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**MAC** aka Message Authentication Code produce from key, message to
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2023-08-24 04:44:53 +00:00
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authentication tag. **HMAC** is MAC using hash.
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- A send B message with MAC (generate from message and A key).
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- B double check message with MAC (generate from receive message and B key).
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- A and B use same key.
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2023-09-10 16:39:41 +00:00
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2023-09-10 16:41:21 +00:00
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```mermaid
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2023-09-10 16:39:41 +00:00
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sequenceDiagram
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participant alice
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participant bob
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alice ->> bob: send username, password
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bob -->> alice: return alice|mac(private_key, alice)
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alice ->> bob: send alice|mac(private_key, alice)
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bob -->> alice: return OK
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alice ->> bob: send bob|mac(private_key, alice)
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bob -->> alice: return ERROR
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```
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