The Certificate and the Signature
How a stranger's key becomes trustworthy. Certificates, chains, revocation, transparency, and what a signature means in law.
Why You Cannot Trust a Key You Were Handed
You will be able to state the introduction problem in one sentence and explain why no amount of cryptography solves it on its own.
11,962 words/52 min read26The Certificate
You will be able to say, in one sentence, what a certificate is and what it is not, without using the word "trust" as a hiding place.
11,536 words/50 min read27The Chain
You will be able to explain why a website certificate is almost never signed directly by anything your computer trusts, and why that is deliberate.
11,998 words/52 min read28The Certificate Authority
You will be able to say in one sentence what a certificate authority actually sells, and why the answer is not "encryption".
11,995 words/52 min read29The Handshake
You will be able to state the three things a TLS connection promises you — secrecy, tamper-detection, and knowing who is at the far end — and say which…
11,994 words/52 min read30Revocation
You will be able to say in one sentence why a certificate must sometimes be cancelled before it expires, and name the three situations that force it.
11,969 words/52 min read31Certificate Transparency
You will be able to explain without jargon why the owner of a domain name once had no way at all of learning that a certificate had been issued for it.
11,991 words/52 min read32The Digital Signature
You will be able to state, in one sentence and without hedging, the only thing a verified digital signature proves, and name the three assumptions that…
13,467 words/59 min read33What a Signature Means in Law
You will be able to name the three legal tiers of electronic signature under European law, state the exact test each one has to pass, and say which of…
13,985 words/61 min read34Time, and Signatures That Must Outlive Their Keys
You will be able to name the three mechanisms by which a good signature becomes unverifiable over time, and say which one is a problem of cryptography…
12,000 words/52 min read35When a Certificate Authority Fails
You will be able to state, in one sentence a non-technical colleague can repeat, why the security of every website on the internet is bounded by the…
13,382 words/58 min read