(PGP is a trademark, and GPG coined to get around it, but you’ll often see PGP used generically to refer to this method of using public keys.) It lets you build a directory of other people’s public keys, while also letting you carry out encryption, decryption, signing, and verifying. PGP is available for the Mac via GPGTools, a version of the free software GPG (GNU Privacy Guard). ( How PGP works is described in Part 1.)Ĭomposing a message in Mail to a recipient whose key is in your local GPG Keychain, the lock icon can be clicked to encrypt the message when sent. The service’s messaging and calling options received scores of 7 out of 7 in the Electronic Frontier Foundation’s secure messaging scorecard.īut most of us don’t live in a walled garden, and one of the company’s founders, Phil Zimmermann, is responsible nearly 25 years ago for turning public-key cryptography into what he called PGP, for Pretty Good Privacy. It starts at $10 per month for unlimited text, calls, video chat, and file transfers among its users. Silent Circle has one of the best options that embeds public-key cryptography, if you can convince all the people with whom you need to communicate to opt in.
The easiest way to solve both problems is to use an end-to-end proprietary ecosystem, but that gets us back, more or less, to iMessage or something similar. The second is existential: Without pre-arrangement, such as meeting in person or a phone call, how do you know that what purports to be someone’s public key is actually that person’s key? The first is pragmatic: Senders and recipients need compatible software tools or plugins, preferably integrated into apps so that little effort is required. And a private key can be used to “sign” a string of text or a document to prove mathematically that only the private key’s possessor could have signed it.īut there are two missing pieces that would let Mac, iOS, and other platforms’ users take advantage of PK. Anything encrypted by someone else with the public key can only be decrypted by having access to the corresponding private key. The public key can be freely distributed. It’s an effective system that has no known theoretical exploits, and currently deployed implementations are considered robust.Īnd to recap: The clever bit with the public-key approach is that you have two complementary keys, one public and one private. In our last episode of Private I, I explained the basics of public-key (PK) cryptography, a way to scramble messages in a way that only someone possessing a particular key can decrypt, without that key ever having to be publicly disclosed or shared.
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