When encryption is used properly, your communications or information should only be readable by you and the person or people you’re communicating with. End-to-end encryption protects your data from surveillance by third parties, but if you’re unsure about the identity of the person you’re talking to, its usefulness is limited. That’s where key verification comes in. By verifying public keys, you and the person with whom you’re communicating add another layer of protection to your conversation by confirming each other’s identities, allowing you to be that much more certain that you’re talking to the right person.
Key verification is a common feature of protocols that use end-to-end encryption, such as PGP and OTR. On Signal, they're called "safety numbers." To verify keys without the risk of interference, it's advisable to use a secondary method of communicating other than the one you’re going to be encrypting; this is called out-of-band verification. For example, if you are verifying your OTR fingerprints, you might email your fingerprints to one another. In that example, email would be the secondary communications channel.
Verifying Keys Out-of-band
There are several ways to do this. If it can be arranged safely and is convenient, it is ideal to verify keys face-to-face. This is often done at key-signing parties or amongst colleagues.
If you cannot meet face-to-face, you can contact your correspondent through a means of communication other than the one for which you’re trying to verify keys. For example, if you’re trying to verify PGP keys with someone, you could use the telephone or an OTR chat to do so.
Regardless of the program that you use, you will always be able to locate both your key and the key of your communication partner.
Although the method of locating your key varies by program, the method of verifying keys remains approximately the same. You can either read your key’s fingerprint aloud (if you are face-to-face or using the telephone) or you can copy and paste it into a communications program, but whichever you choose, it is imperative that you check every single letter and numeral.
Tip: Try verifying keys with one of your friends. To learn how to verify keys in a specific program, visit that program’s how-to guide.