Computer Science › Section M · Theory of computation › Topic M.6
Public-key cryptography
Hard problems are usually obstacles, but cryptography turns one into a shield. RSA lets anyone lock a message with a published key while only the owner can unlock it, because multiplying two primes is easy and undoing the multiplication, as far as anyone knows, is not.
In this topic
- Turning hardness into an asset
- Modular arithmetic
- Setting up RSA keys
- Encrypting and decrypting
- Worked example: building keys and sending a letter
- Why decryption works
- Worked example: breaking a small key
- Why big keys are safe
- What the security rests on
- Signatures and real-world use
- Common mistakes to avoid
- Key takeaways
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