Pretty Good Privacy in the context of Public-key cryptography

Briar is an open-source software communication technology, intended to provide secure and resilient peer-to-peer communications with no centralized servers and minimal reliance on external infrastructure. Messages can be transmitted through Bluetooth, Wi-Fi, over the internet via Tor or removable storage, such as USB sticks. All communication is end-to-end encrypted. Relevant content is stored in encrypted form on participating devices. Long-term plans for the project include support for distributed applications such as crisis mapping and collaborative document editing.

The initial target audience for Briar includes "activists, journalists and civil society" with plans to make the system "simple enough to help anyone keep their data safe." As the ability to function in the absence of internet infrastructure may also make the project valuable to disaster response and aid organizations, the developers are working with the Open Humanitarian Initiative and Taarifa. Ultimately, the developers aim to create a system which is "as simple to use as WhatsApp, as secure as PGP, and that keeps working if somebody breaks the Internet." It is possible for an Android device to download Briar from another Android device which already has Briar installed.

Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic algorithms based on mathematical problems termed one-way functions. Security of public-key cryptography depends on keeping the private key secret; the public key can be openly distributed without compromising security. There are many kinds of public-key cryptosystems, with different security goals, including digital signature, Diffie–Hellman key exchange, public-key key encapsulation, and public-key encryption.

Public key algorithms are fundamental security primitives in modern cryptosystems, including applications and protocols that offer assurance of the confidentiality and authenticity of electronic communications and data storage. They underpin numerous Internet standards, such as Transport Layer Security (TLS), SSH, S/MIME, and PGP. Compared to symmetric cryptography, public-key cryptography can be too slow for many purposes, so these protocols often combine symmetric cryptography with public-key cryptography in hybrid cryptosystems.