Lesson 202
Public-Key Cryptography
Asymmetric keys · RSA · Diffie–Hellman
1:00How asymmetric key pairs, RSA, and Diffie-Hellman solve the key-distribution problem using trapdoor one-way functions.
By the end, you can
- Explain the key-distribution problem and why it makes symmetric-only systems fragile.
- State which key encrypts and which decrypts in an asymmetric scheme, and why the directions matter.
- Define a trapdoor one-way function and identify its three properties.
- Trace RSA key generation from two primes through n, φ(n), e, and d.
- Compute RSA encryption (c = m<sup>e</sup> mod n) and decryption (m = c<sup>d</sup> mod n) on small examples.
- Describe the Diffie–Hellman exchange step by step and compute the shared secret from small numbers.
- Explain the discrete-logarithm problem and why it protects the DH shared secret.
- Describe how hybrid encryption works and why public-key crypto does not replace symmetric ciphers.
- Compare ECC and RSA key sizes for equivalent security levels.
- Identify the two common myths about public-key cryptography.
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