Plugin: crypto

• infos = Information about crypto plugin is in keys below
• infos/author = Peter Nirschl peter.nosp@m..nir.nosp@m.schl@.nosp@m.gmai.nosp@m.l.com
• infos/licence = BSD
• infos/provides = filefilter
• infos/needs =
• infos/recommends =
• infos/placements = postgetstorage presetstorage #ifdef ELEKTRA_CRYPTO_API_GCRYPT {#src_plugins_crypto_README_md}
• infos/status = experimental unfinished memleak discouraged #else
• infos/status = experimental unfinished discouraged #endif
• infos/metadata = crypto/encrypt
• infos/description = Cryptographic operations

Crypto Plugin

Introduction

This plugin is a filter plugin allowing Elektra to encrypt values before they are persisted and to decrypt values after they have been read from a backend.

The idea is to provide protection of sensible values before they are persisted. This means the value of a key needs to be encrypted before it is written to a file or a database. It also needs to be decrypted whenever an admissible access (read) is being performed.

The users of Elektra should not be bothered too much with the internals of the cryptographic operations. Also the cryptographic keys must never be exposed to the outside of the crypto module.

The crypto plugin supports different libraries as provider for the cryptographic operations. At the moment the following crypto APIs are supported:

• OpenSSL (libcrypto)
• libgcrypt

Dependencies

#ifdef ELEKTRA_CRYPTO_API_GCRYPT

• libgcrypt20-dev or libgcrypt-devel #endif #ifdef ELEKTRA_CRYPTO_API_OPENSSL
• libssl-dev or openssl-devel #endif

How to compile

The following compile variants are available:

1. crypto_gcrypt
2. crypto_openssl

Add "crypto" and the variants, that you want (you can add one of them or all), to the PLUGINS variable in CMakeCache.txt and re-run cmake.

In order to add all compile variants you can add "CRYPTO" to the PLUGINS variable.

An example CMakeCache.txt may contain the following variable:

PLUGINS=crypto;crypto_gcrypt;crypto_openssl

or it may look like:

PLUGINS=CRYPTO

Manual Library Setup

If you have a custom built OpenSSL or libgcrypt on your system, you can tell CMake to use those by setting the following CMake variables.

For a custom OpenSSL location set:

• OPENSSL_INCLUDE_DIR to the library's header files
• OPENSSL_LIBRARIES to the library's binary file

For a custom libgcrypt location set:

• LIBGCRYPT_INCLUDE_DIR to the library's header files
• LIBGCRYPT_LIBRARIES to the library's binary file

Mac OS X

Both variants of the plugin compile under Mac OS X "El Capitan" (Version 10.11.3 (15D21)).

For the crypto_gcrypt variant download and install either MacPorts or Homebrew. Use one of those tools to download and install libgcrypt. If you choose MacPorts, you can set the CMake variables like this:

• LIBGCRYPT_INCLUDE_DIR to /opt/local/include/
• LIBGCRYPT_LIBRARIES to /opt/local/lib/libgcrypt.dylib

The CMake command might look something like:

    cmake -DLIBGCRYPT_INCLUDE_DIR="/opt/local/include/" -DLIBGCRYPT_LIBRARIES="/opt/local/lib/libgcrypt.dylib" -DPLUGINS="crypto;crypto_gcrypt;" /path_to_elektra_src

For the crypto_openssl variant a custom-built OpenSSL library is neccessary as the MacPorts or Homebrew variants do not seem to work. Download the latest version of the OpenSSL library from the project homepage and compile it. Copy the header files and the binary files to a location where all users can access them.

Set the CMake variables OPENSSL_INCLUDE_DIR and OPENSSL_LIBRARIES to your desired location.

Restrictions

The crypto plugin will encrypt and decrypt values using AES-256 in CBC mode.

The key derivation is still WIP.

Planned Features

• Encryption of values
• Decryption of values
• Key derivation by metadata (password provided within a meta-key)
• Key derivation by using a specified key-file (like the SSH client does)
• Key derivation by utilizing the pgp-agent

The encryption and decryption of values is a straight forward process, once the key and IV are supplied. The key-derivation process in a library is a bit tricky.

The crypto plugin itself can hold configuration data about the order of the applied key derivation functions. For example, if a password is provided by a meta-key, it will be used, otherwise we look for a key file. If no key file has been configured, we try to trigger the PGP agent, etc.

The following example configuration illustrates this concept:

    system/elektra/crypto/config/key-derivation/#0 = meta
    system/elektra/crypto/config/key-derivation/#1 = file
    system/elektra/crypto/config/key-derivation/#2 = agent
    system/elektra/crypto/config/key-file/path/#0 = ~/.elektra/id_aes
    system/elektra/crypto/config/key-file/path/#1 = /etc/elektra/id_aes

Only keys marked with a certain meta-key will be considered for encryption/decryption.

Examples

Metadata based encyption

You specify the parameters of the cryptographic operations in a KeySet together with the keys to be encrypted. The following parameters are required:

• Key - the symmetric cryptographic key for encryption
• IV - the initialization vector (IV) that is required by the CBC mode

The following keys are required for metadata based encryption:

    /elektra/modules/crypto/key
    /elektra/modules/crypto/iv

You can use the following meta-key to mark a key for encryption:

    crypto/encrypt

If this meta-key has a value with a string-length greater than 0 (strlen() > 0) then the crypto-plugin will try to encrypt it.