Concord is a Blockstack app that lets you create secure digitally signed micro agreements with a counter party. To use Concord, you will be prompted to create a Blockstack ID if you do not already have one. Once you are signed in using Blockstack, you can add other Blockstack users as contacts using their Blockstack name.
Agreements can be created only with Blockstack users who have already installed the app and have been added as contacts.Your agreements and contacts are backed up to Blockstack's Gaia storage, and content is encrypted so that only the app user can ever read it.
Cryptographic keys used by Blockstack to sign and encrypt your agreements never leave your device. This ensured that only you truly own your data.