Cryptography and digital signatures explained

Cryptography achieves two basic things for us:
1. We can lock a document (with our private key) so that only we or someone to whom we gave a key (a Public key) is able to open and read it. But not change it or create new documents.
2. If we have been given a key (Public key) and we receive a document, we can be confident that if the private key succeeds in opening the document, then it can only have come from the person who owns the Public key. This use of the keys is also described as “Digital Signatures”
Lets say I am a politician and I want to exchange a confidential documents with my friend Hilary. First I create a Public key on my compute, there is fee software for doing this. I then create a public key and I give this key to Hilary, who puts it safely in a key store on her computer.
I can then encrypt a document with my Private key and pass it to Hilary knowing that only she can open it and that when it opens successfully she will be sure that it is from me and nobody else.

Setting these up is fiddly but not beyond the average person with a bit of stamina. Most email clients have a way to attach encryption to your email and communicate securely with someone.

The “Explained series” is planned to build into a trustworthy collection of explanations and commentaries that can be trusted to tell the story straight without any bias and attempt to make the subjects accessible to the layman. The latter is not always easy as some of these terms refer to genuinely complex subject matter, while others are simply too vague to pin down (there’s another word for that).
If you want an answer on something and you can’t find it easily, please use the comments section to just ask and I will appreciate not having to research the next topic.

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