## Introduction

This documents describes how to make secure shipments with the R package sship. While sship provides technical means of very strong protections through encryption of digital content all still depends on proper and knowledgeable use. Therefore, please take a moment and study the next paragraph very carefully.

sship makes sure that a secret will only be available to the recipient by applying the recipient’s public key. When sship is to be used for sending a secret to a recipient one must be absolutely sure that the public key used by sship belongs to the intended recipient. The authenticity of the public key should be established by a combination of technical and social means. Technically, the public key should be managed (by its owner, the recipient) through a key provider that enforces multi-factor authentication of its users. Socially, the two parties to share a secret should know of each other (personally, professionally or similar) and establish trust both between themselves and the technology to be used to ensure authenticity of the public key.

Following is an example of how the authenticity of a public key may be sufficiently established. Person or entity X needs to send a secret data file to person or entity Y and therefor need Y’s public key. A public key provider exists (e.g. GitHub) and at this provider X has made a dedicated group (or organization in GitHub-terms) that enforces multi-factor authentication of its members. X asks Y to apply for a membership of this group at the public key provider. X now expects a member request from Y and grants it as it arrives. Since multi-factor authentication is enforced it is unlikely that anyone else but Y may add, alter or delete Y’s public key at the provider. X can thereafter collect Y’s public key from the provider at any time and be sufficiently sure that it will be authentic.

## How to

Basically, sship can be used for three things: encrypt files, send encrypted files and decrypt files. The latter is described in the article Extract cargo from a secure shipment. Encryption and sending (shipment) of files will be the subjects for the remaining part of this article.

### Encrypt (secure) a file and send (ship) it

Both encryption and shipment can be obtained in one operation with the R function sship():

sship(content, recipient, pubkey_holder, vessel, declaration)

where content is the path to the file to be encrypted, recipient is the unique user id of the recipient at the public key provider, pubkey_holder is a reference to a known public key provider (see Configure sship below), vessel is a reference to the transportation method (see also Configure sship below) and declaration is an optional “freight paper rubber stamp” to be associated with the shipment. A practical example may look something like this:

sship("secret_data.csv", "myfriend", "github", "ftp", "pickable")

which will collect myfriend’s public key from github and use it in the encryption process of secret_data.csv before shipping it with ftp. Immediately after an empty file named pickable is shipped using the same route. myfriend can now check if the shipment has arrived by polling for a file named pickable and collect the shipment before starting the process of unwrapping and decryption.

### Configure sship

Some of the above arguments to sship() are just references to the actual values that are stored in a configuration file. sship comes with a default configuration but most likely this will not be sufficient. A local config can be made by calling the create_config() R function found in sship (output also shown):

create_config()
[1] "./_sship.yml file created: fill it in"

In the above example of the R function sship() the references github and ftp depends on configuration for the function to obtain proper values. The reference github already has a working setup in the default configuration, but ftp has not. To accomplish this open the file _sship.yml, find the appropriate section and edit accordingly:

...
recipient:
bob:
ftp:
host: ftp.here.no
port: 21
path: path/to/myfriend
user: myfriend
...
ship can also be applied as a tool in a centralized or server-like environment where requirements for management and configuration may differ from a local instance running R. Every time sship needs information from configuration setting it looks for it in several places. For a server setup the place to look for sship’s configuration can be provided by setting the environmental variable R_SSHIP_CONFIG_PATH to the directory where the configuration is to be found. Making R_SSHIP_CONFIG_PATH accessible in an R session, sship will abide by its value. However, if a local file named _sship.yml exists in the current working directory it it will take precedence over the one defined by R_SSHIP_CONFIG_PATH.