Written in 2014 for OpenBSD, signify is a tool to cryptographically sign and verify files: 
It only supports a single algorithm, Ed25519, created by djb and his gang. It’s fast, immune to timing attacks by design, produce deterministic signatures, uses small keys and produce small signatures, … it does look like a sound choice.
Signify's main benefits is that it has a small codebase and is not based on GnuPG. On the downside, there is no revocation mechanism  and the trust path relies on getting the key directly from a trusted developer. 
Signify's usage is not just limited to OpenBSD and the tool has also been been packaged in Debian.  To learn more about signify, refer to this blog post by the original author.
Installation and Usage
In the steps below, installing package
qrencode is optional and only needed if you intend to create QR codes.
1. Install signify.
1. Update the package lists.
sudo apt update
2. Upgrade the system.
sudo apt full-upgrade
3. Install the
signify-openbsd qrencode package.
apt command line parameter
--no-install-recommends is in most cases optional.
sudo apt install --no-install-recommends signify-openbsd qrencode
The procedure of installing
signify-openbsd qrencode is complete.
2. Create a key.
This only needs to be done once unless multiple keys are desired; in that case different key names should be used. In the following example,
keyname is used as the sample key name.
signify-openbsd -G -p keyname.pub -s keyname.sec
3. Optional: Add a key comment.
comments here with the actual comment but keep the
". The comment could be a name, position, website, e-mail address and/or anything else.
signify-openbsd -G -p keyname.pub -s keyname.sec -c "comments here"
- The private key file
keyname.sec needs to stay private -- never share
keyname.sec with anyone as this would defeat the purpose of signing files!
- The public key file
keyname.pub can be shared with anyone.
4. Utilize signify.
To sign a file
message.txt (which has to be created by the user beforehand).
signify-openbsd -S -s keyname.sec -m message.txt
This will create a signature file
To verify a file
message.txt with signature file
signify-openbsd -V -p keyname.pub -m message.txt
5. Optional: Create a QR code for the public key.
qrencode -r keyname.pub -o keyname.pub.png
keyname.pub.png would be the QR code of the public key.
Refer to the Debian signify-openbsd Manual Page for further options.