How Do You Know It’s Really Cynthia Armistead?

Introduction to PGP

What on earth is that mess of let­ters and num­bers at the end of some folks’ email and Usenet mes­sages? In many cas­es1, it’s a PGP sig­na­ture. As an exam­ple, here’s a plain text mes­sage I wrote: 

This is a PGP-signed message. The signature will be longer for longer

After I signed it with PGP, it looks like this:


This is a PGP-signed message. The signature will be longer for longer


Version: PGP Personal Privacy 6.5.8
Comment: See for further info


PGP is the best-known pub­lic-key encryp­tion method in use on the inter­net. If I sign a mes­sage I post to a par­tic­u­lar news­group using my pri­vate key, any­one who wish­es to ver­i­fy that it is from me and unal­tered can check the sig­na­ture on the mes­sage using my pub­lic key. If the mes­sage has been altered in any way, the sig­na­ture will not be valid. If some­one else forged a mes­sage in my name and tried to copy the sig­na­ture from one of my real posts, the sig­na­ture would­n’t check as valid on the forged mes­sage. That’s the rea­son I use it. 

Some peo­ple use PGP for actu­al encryp­tion. If I want­ed to send my friend Doug an email that con­tained very sen­si­tive infor­ma­tion, I’d write my mes­sage and sign it with my pri­vate key. I would then encrypt it with Doug’s pub­lic key, and email the encrypt­ed ver­sion to him. Upon receipt, he would decrypt the mes­sage using his pri­vate key, then check my sig­na­ture using my pub­lic key. We’d know that the mes­sage had not been read by any­one but us, and had not been altered in any way. I find very lit­tle need for encryp­tion, but some peo­ple use it frequently. 

For a far more thor­ough expla­na­tion of PGP, please check the FAQ.

The last time I checked, Syman­tec owned PGP. You can still get a free­ware imple­men­ta­tion of OpenPGP (one of its descen­dants) at Gnu Pri­va­cy Guard. If you want to use encryp­tion for your email, Hush­mail is very easy to use. 

Want my key?

Some oth­er links you may find use­ful as you explore PGP: 

Last updat­ed 12 Sep­tem­ber 2021. 

1 Some­times a list of weird char­ac­ters at the end of a mes­sage is the sender’s geek code, or sim­i­lar code spe­cif­ic to a par­tic­u­lar inter­est group.