Upspin architecture

Each user of the system is represented by an Upspin user name, which looks like an email address; a public/private key pair; and the network address of a directory server:

User diagram

That directory server holds a hierarchical tree of names pointing to the user’s data, which is held in a store server, possibly encrypted. Each item in the tree is represented by a directory entry containing a list of references that point to data in the store server:

Directory and Store server diagram

All the users are connected through a central key server at, which holds the public key and directory server address for each user.

Key server diagram

This is how the pieces fit together:

Overall system diagram

From top to bottom, these represent:

To illustrate the relationship between these components, here is the sequence of requests a client exchanges with the servers to read the file

Reading a file diagram

  1. The client asks the key server for the record describing the owner of the file, which is the user name at the beginning of the file name ( The key server’s response contains the name of the directory server holding that user’s tree ( and Augie’s public key.
  2. The client asks the directory server for the directory entry describing the file. The response contains a list of block references, which include the name of the store server (
  3. The client can then ask the store server for each of the blocks, pipelining the requests for efficiency.
  4. The client decrypts the blocks (using Augie’s public key) and concatenates them to assemble the file.