Secure Asynchronous File Transfer



SAFT enables the secure asynchronous transfer of files on low-trust networks with bad connectivity. Asynchonous here means that only the sender needs to be online to start the transfer, while the recipient can initiate their end at any time. Intermediate nodes can easily be set up and store some or all file fragments for future transfer. The intermediate SAFT nodes can't access the data, and can therefore - if the need arises - forward some or all file fragments to any other intermediate SAFT node without compromising security or data integrity.


SAFT consists of two main parts:

  • The client nodes (endpoints) that send and receive files.
  • The intermediate nodes that store and/or forward the files to their final destination.

Use Cases

SAFT enables:

  • Easy transfer of arbitrarily large files over low-trust networks
  • Storage of sensitive files on unknown or uncertain third-party servers

Example #1: An embassy needs to transfer documents

An embassy has very sensitive documents it needs to send back to its home country with a guarantee that they reach their destination. The host country is notorious for spying on both enemies and allies, and the embassy can therefore not trust that their documents are safely transferred on the unstable local network. Back at home, the embassy has access to governmental infrastructure to store their documents and transfer them to the intended agency - but due to corruption, the ambassador knows not to trust anyone but the final recipient. SAFT helps solve all their problems.

Example #2: Backup of personal pictures

A couple is on vacation and takes lots of pictures of their travels. As they are afraid to accidentally lose all the pictures, they want to back them up in the cloud. They have found a service that provides very good bandwidth and uptime, but as there are some pictures that they don't want anyone to see - and because they are smart - they know not to trust them with their personal data, only to trust their performance. They can back the pictures up using SAFT, and safely download them when they come home from their travels.


SAFT provides:

  • An end-to-end encrypted channel for transfer of files
  • Asynchronicity - only the sender needs to be online for transfer to occur *
  • A guarantee of transfer of responsibility *
  • A guarantee of completion of synchronous transfer
  • A guarantee of completion of asynchronous transfer *

    * SAFT can not guarantee that the owner of the intermediate node actually forwards the file, it only provides the protocol for doing so. However, a sending node can send to any number of intermediate nodes for higher rate of success.


Sending a file

Receiving a file

Acting as an intermediate node

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