Using Digital Keys

• How do you sign something digitally, and why would you consider that?
• Is it possible to send encrypted email without the use of a service like Protonmail?
• What is a key pair, and how does it figure into the equation?

While enabling digital signatures and encryption may be a little scary and seem like deeper technical water, it’s really fairly simple to enable, though it requires several steps. Let’s start with a clear understanding of the concept of how a public/private key system works.

What are Public and Private Keys?

Each key is a file containing a string of binary data. This data can be used by algorithms that can verify the public key belongs to, or matches, the private key, and vice versa. They’re called “public” or “private” because the public key is freely distributed, while the private key is kept secure by the owner.

How Are Keys Used to Encrypt?

When Mike and Mary are conversing in ways that require signing or encryption, each uses a key generation program to create their own pair of public and private keys. They then distribute their public keys freely to anyone who is interested in receiving encrypted email or verifying their electronic signature. (see fig. 1)

figure 1. Generating public/private key pairs

Each then stores their private key securely on their local system.

When Mike wants to send Mary an encrypted message, he uses the public key she’s provided to encrypt. Then when Mary receives the encrypted message, she uses her private key to decrypt it. (see fig. 2)

figure 2. Using keys for encryption

How are Keys Used to Digitally Sign?

Signing works the same way as encryption, but the private key is used to sign, and the public key is used to verify the signature.

Electronic signatures can be applied to individual emails or to documents. See figure 3 for an example of a signed MS Word document.

figure 3. A signed MS Word document

That’s it!

Both Windows and Linux provide software to generate keys and to verify signatures as well as encrypt/decrypt documents and messages at no additional cost. How software is used to generate and employ keys varies from system to system, so we’re not going to try to cover all the variations here. Plenty of well-written web pages are waiting for you out there.