About
Classical cryptography, explained and grounded
Classical Crypto Today is a reference for the cryptography actually running the internet right now — RSA, ECC, Diffie-Hellman, AES, SHA-2, TLS — the algorithms that post-quantum cryptography is set to replace. Understanding what's being replaced, and why, turns out to be the fastest way to understand what comes next.
Every claim on this site is meant to be checkable. Diagrams are computed from the real math, not hand-waved; Playground tools run your browser's actual Web Crypto API, not a simulation; and every module traces back to a real standard, RFC, or paper — listed in full on the References page.
What's here
Pick a persona — executive, GRC, developer, architect, IT ops, researcher, or curious — and get a reading path tailored to it. Nothing is hidden from anyone; a persona just reorders what you see first.
Learn →21 modules, from the history of cryptography through RSA, ECC, AES, TLS, and the post-quantum threat, each with diagrams, worked examples, and real formulas.
Playground →10 tools that run real cryptography in your browser via the Web Crypto API — AES-GCM, RSA-OAEP, ECDSA, X3DH, and more. Nothing is simulated, and nothing leaves your browser.
Navigate →Every module, tool, and category as a single connected graph, for when you'd rather explore by clicking around than by reading a list.
Compare →Side-by-side cheat sheets — RSA vs. ECC vs. Diffie-Hellman, AES modes, hash functions — for when you already know the material and just need the numbers.
Glossary →76 terms used across the site, defined plainly and linked back to the module that covers each one in depth.
Checklist →A practical PQC-migration inventory for GRC and architecture teams — not a compliance audit, a starting point.
Assess →Eight questions about what you actually run today, mapped to a prioritized reading list.
What this deliberately isn't
This isn't a compliance tool, a certification body, or a vendor evaluation platform — the Assess quiz and migration checklist are explicitly starting points for a conversation, not a substitute for a real cryptographic inventory or an audit.
There's no scoring or trust-rating system for the content itself, no login, no tracking of what you read, and nothing you type into a Playground tool or the checklist is ever sent to a server — the checklist saves to your browser's local storage only, and every cryptographic operation runs entirely client-side.
Open source
The full source — content, diagrams, and every Playground tool — is public on GitHub. Corrections, issues, and pull requests are welcome.