.. _object-storage:


Cloud Object Storage plugins
============================

.. contents::

   
Introduction
------------

Osimis freely provides the `source code
<https://hg.orthanc-server.com/orthanc-object-storage/file/default/>`__ of 3 plugins
to store the Orthanc files in `Object Storage <https://en.wikipedia.org/wiki/Object_storage>`__
at the 3 main providers: `AWS <https://aws.amazon.com/s3/>`__, 
`Azure <https://azure.microsoft.com/en-us/services/storage/blobs/>`__ & 
`Google Cloud <https://cloud.google.com/storage>`__

Storing Orthanc files in object storage and your index SQL in a 
managed database allows you to have a stateless Orthanc that does
not store any data in its local file system which is highly recommended
when deploying an application in the cloud.


Compilation
-----------

.. highlight:: text

The procedure to compile the plugins is quite similar of that for the
:ref:`core of Orthanc <compiling>` although they usually require 
some prerequisites.  The documented procedure has been tested only
on a Debian Buster machine.

The compilation of each plugin produces a shared library that contains 
the plugin.

Given thes plugins are used to interface with a commercial & proprietary
service, pre-compiled Windows/Docker binaries are available only for
companies who have subscribed for a `support contract <https://www.osimis.io/en/services.html#cloud-plugins>`__ at Osimis.


AWS S3 plugin
^^^^^^^^^^^^^

Prerequisites: Compile the AWS C++ SDK::

  $ mkdir ~/aws
  $ cd ~/aws
  $ git clone https://github.com/aws/aws-sdk-cpp.git
  $ 
  $ mkdir -p ~/aws/builds/aws-sdk-cpp
  $ cd ~/aws/builds/aws-sdk-cpp
  $ cmake -DBUILD_ONLY="s3;transfer" ~/aws/aws-sdk-cpp 
  $ make -j 4 
  $ make install

Prerequisites: Install `vcpkg <https://github.com/Microsoft/vcpkg>`__ dependencies::

  $ ./vcpkg install cryptopp

Compile::

  $ mkdir -p build/aws
  $ cd build/aws
  $ cmake -DCMAKE_TOOLCHAIN_FILE=[vcpkg root]\scripts\buildsystems\vcpkg.cmake ../../orthanc-object-storage/Aws

Azure Blob Storage plugin
^^^^^^^^^^^^^^^^^^^^^^^^^

Prerequisites: Install `vcpkg <https://github.com/Microsoft/vcpkg>`__ dependencies::

  $ ./vcpkg install cpprestsdk


Compile::

  $ mkdir -p build/azure
  $ cd build/azure
  $ cmake -DCMAKE_TOOLCHAIN_FILE=[vcpkg root]\scripts\buildsystems\vcpkg.cmake ../../orthanc-object-storage/Azure

Google Storage plugin
^^^^^^^^^^^^^^^^^^^^^

Prerequisites: Install `vcpkg <https://github.com/Microsoft/vcpkg>`__ dependencies::

  $ ./vcpkg install google-cloud-cpp
  $ ./vcpkg install cryptopp

Compile::

  $ mkdir -p build/google
  $ cd build/google
  $ cmake -DCMAKE_TOOLCHAIN_FILE=[vcpkg root]\scripts\buildsystems\vcpkg.cmake ../../orthanc-object-storage/google


Configuration
-------------

.. highlight:: json

AWS S3 plugin
^^^^^^^^^^^^^

Sample configuration::

  "AwsS3Storage" : {
  	"BucketName": "test-orthanc-s3-plugin",
    "Region" : "eu-central-1",
    "AccessKey" : "AKXXX",
    "SecretKey" : "RhYYYY"
  }

Azure Blob Storage plugin
^^^^^^^^^^^^^^^^^^^^^^^^^

Sample configuration::

  "AzureBlobStorage" : {
    "ConnectionString": "DefaultEndpointsProtocol=https;AccountName=xxxxxxxxx;AccountKey=yyyyyyyy===;EndpointSuffix=core.windows.net",
    "ContainerName" : "test-orthanc-storage-plugin"
  }


Google Storage plugin
^^^^^^^^^^^^^^^^^^^^^

Sample configuration::

  "GoogleCloudStorage" : {
    "ServiceAccountFile": "/path/to/googleServiceAccountFile.json",
    "BucketName": "test-orthanc-storage-plugin"
  }


Client-side encryption
----------------------

Although all cloud providers already provide encryption at rest, the plugins provide
an optional layer of client-side encryption .  It is very important that you understand 
the scope and benefits of this additional layer of encryption.

Rationale
^^^^^^^^^

Encryption at rest provided by cloud providers basically compares with a file-system disk encryption.  
If someone has access to the disk, he won't have access to your data without the encryption key.

With cloud encryption at rest only, if someone has access to the "api-key" of your storage or if one 
of your admin inadvertently make your storage public, `PHI <https://en.wikipedia.org/wiki/Protected_health_information>`__ will leak.

Once you use client-side encryption, you'll basically store packets of meaningless bytes on the cloud infrastructure.  
So, if an "api-key" leaks or if the storage is misconfigured, packets of bytes will leak but not PHI since
no one will be able to decrypt them.

Another advantage is that these packets of bytes might eventually not be considered as PHI anymore and eventually 
help you meet your local regulations (Please check your local regulations).

However, note that, if you're running entirely in a cloud environment, your decryption keys will still 
be stored on the cloud infrastructure (VM disks - process RAM) and an attacker could still eventually gain access to this keys.  
Furthermore, in the scope of the `Cloud Act <https://en.wikipedia.org/wiki/CLOUD_Act>`__ , the cloud provider might still have 
the possibility to retrieve your data and encryption key (while it will still be more complex than with standard encryption at rest).

If Orthanc is running in your infrastructure with the Index DB on your infrastructure, and files are store in the cloud, 
the master keys will remain on your infrastructure only and there's no way the data stored in the cloud could be decrypted outside your infrastructure.

Also note that, although the cloud providers also provide client-side encryption, we, as an open-source project, 
wanted to provide our own implementation on which you'll have full control and extension capabilities.  
This also allows us to implement the same logic on all cloud providers.

Our encryption is based on well-known standards (see below).  Since it is documented and the source code is open-source, 
feel-free to have your security expert review it before using it in a production environment.

Technical details
^^^^^^^^^^^^^^^^^

Orthanc saves 2 kind of files: DICOM files and JSON summaries of DICOM files.  Both files contain PHI.

When configuring the plugin, you'll have to provide a `Master Key` that we can also call the `Key Encryption Key` (KEK).

For each file being saved, the plugin will generate a new `Data Encryption Key` (DEK).  This DEK, encrypted with the KEK will be pre-pended to the file.

If, at any point, your KEK leaks or you want to rotate your KEKs, you'll be able to use a new one to encrypt new files that are being added 
and still use the old ones to decrypt data.  You could then eventually start a side script to remove usages of the leaked/obsolete KEKs.

To summarize:

- We use `Crypto++<https://www.cryptopp.com/>`__ to perform all encryptions.  
- All keys (KEK and DEK) are AES-256 keys.
- DEKs and IVs are encrypted by KEK using CTR block cipher using a null IV.
- data is encrypted by DEK using GCM block cipher that will also perform integrity check on the whole file.

The format of data stored on disk is therefore the following:

- **VERSION HEADER**: 2 bytes: identify the structure of the following data currently `A1`
- **MASTER KEY ID**: 4 bytes: a numerical ID of the KEK that was used to encrypt the DEK
- **EIV**: 32 bytes: IV used by DEK for data encryption; encrypted by KEK
- **EDEK**: 32 bytes: the DEK encrypted by the KEK.
- **CIPHER TEXT**: variable length: the DICOM/JSON file encrypted by the DEK
- **TAG**: 16 bytes: integrity check performed on the whole encrypted file (including header, master key id, EIV and EDEK)

Configuration
^^^^^^^^^^^^^

.. highlight:: text

AES Keys shall be 32 bytes long (256 bits) and encoded in base64.  Here's a sample OpenSSL command to generate such a key::

  openssl rand -base64 -out /tmp/test.key 32

Each key must have a unique id that is a uint32 number.

.. highlight:: json

Here's a sample configuration file of the `StorageEncryption` section of the plugins::

  {
    "StorageEncryption" : {
      "Enable": true,
      "MasterKey": [3, "/path/to/master.key"], // key id - path to the base64 encoded key
      "PreviousMasterKeys" : [
          [1, "/path/to/previous1.key"],
          [2, "/path/to/previous2.key"]
      ],
      "MaxConcurrentInputSize" : 1024   // size in MB 
    }
  }

**MaxConcurrentInputSize**: Since the memory used during encryption/decryption can grow up to a bit more 
than 2 times the input, we want to limit the number of threads doing concurrent processing according 
to the available memory instead of the number of concurrent threads.  Therefore, if you're currently
ingesting small files, you can have a lot of thread working together while, if you're ingesting large 
files, threads might have to wait before receiving a "slot" to access the encryption module.