Cloud Object Storage plugins

Introduction

Osimis freely provides the source code of 3 plugins to store the Orthanc files in Object Storage at the 3 main providers: AWS, Azure & Google Cloud

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.

Pre-compiled binaries

These plugins are used to interface Orthanc with commercial and proprietary cloud services that you accept to pay. As a consequence, the Orthanc project doesn’t freely provide pre-compiled binaries for Docker, Windows, Linux or OS X. These pre-compiled binaries do exist, but are reserved to the companies who have subscribed to a professional support contract by Osimis. Although you are obviously free to compile these plugins by yourself (instructions are given below), purchasing such support contracts makes the Orthanc project sustainable in the long term, to the benefit of the worldwide community of medical imaging.

Compilation

The procedure to compile the plugins is quite similar of that for the core of Orthanc 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.

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 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 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 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

AWS S3 plugin

Sample configuration:

"AwsS3Storage" : {
      "BucketName": "test-orthanc-s3-plugin",
  "Region" : "eu-central-1",
  "AccessKey" : "AKXXX",
  "SecretKey" : "RhYYYY",
  "Endpoint": "",                 // optional - currently in mainline version only: custom endpoint
  "ConnectionTimeout": 30,        // optional - currently in mainline version only: connection timeout in seconds
  "RequestTimeout": 1200          // optional - currently in mainline version only: request timeout in seconds (max time to upload/download a file)
}

The EndPoint configuration is used when accessing an S3 compatible cloud provider. I.e. here is a configuration to store data on Scaleway:

"AwsS3Storage" : {
   "BucketName": "test-orthanc",
   "Region": "fr-par",
   "AccessKey": "XXX",
   "SecretKey": "YYY",
   "Endpoint": "s3.fr-par.scw.cloud"
 },

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"
}

Sample setups

You’ll find sample deployments and more info in the Orthanc Setup Samples repository .

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 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.

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++ 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

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.

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.