Security Top

The tools that secure protocols are built from, shown with no protocol around them. Where they are used for the web, see Web Security on the networking page .

Interactive views

• Security Primitives — a hash, a shared key, a key pair, a signature, an HMAC and a Diffie-Hellman key agreement, played by Alice and Bob on a wire that Eve reads and Mallory sits on

On the command line

Each primitive tried by hand with openssl and sha256sum on Ubuntu 26.04, one step per command:

• Part 1: Hash Functions — sha256sum on a real document, one changed bit, checking a download
• Part 2: Shared-Key Encryption — AES with a key and an IV given by hand, and a ciphertext changed without the key
• Part 3: Key Pairs — an RSA key pair, its numbers, and the public half computed from the private one
• Part 4: Public-Key Encryption — RSA-OAEP to Bob's public key, its size limit, and a key wrapped by hand
• Part 5: Signatures — the digest first, then the private key, and the digest read back out of the signature
• Part 6: HMAC — a tag made with a shared key, built again by hand from two SHA-256 runs
• Part 7: Key Agreement — X25519 shares, Mallory in the middle, and a signed share