Asherah

An application-layer encryption SDK that provides advanced encryption features and defense in depth against compromise.

Its goal is to provide an easy-to-use library which abstracts away internal complexity and provides rapid, frequent key rotation with enterprise scale in mind.

Table of Contents

• Introduction
• Getting Started
• Sample Applications
• Further Reading
• Supported Languages
  • Feature Support
• Contributing

Introduction

Asherah makes use of multiple layers of keys in conjunction with a technique known as "envelope encryption". Envelope encryption is a practice where a key used to encrypt data is itself encrypted by a higher-order key and stored alongside the encrypted data, hence forming an envelope structure. The master key used at the root of the key hierarchy is typically managed by a Hardware Security Module (HSM) or Key Management Service (KMS).

The SDK generates cryptographically strong intermediate keys in the hierarchical model and manages their storage via a pluggable backing datastore. The integration with a HSM or KMS provider for the root (master) key in the hierarchy is implemented using a similar pluggable model. This allows for supporting a wide variety of datastores and cloud providers for different architectures.

The SDK provides implementations in multiple languages using native interoperability mechanisms to securely manage and cache internally-generated keys in off-heap protected memory. The combination of secure memory management and the hierarchical key model's partitioning help minimize attack exposure in the event of compromise. Using the protected memory cache has an added benefit of reducing interactions with external resources to improve latency and minimize incurred costs.

Getting Started

The basic use of the SDK proceeds in 3 steps:

Step 1: Create a session factory

A session factory is required to generate encryption/decryption sessions. For simplicity, the session factory uses the builder pattern, specifically a step builder. This ensures all required properties are set before a factory is built.

To obtain an instance of the builder, use the static factory method newBuilder. Once you have a builder, you can use the withXXX setter methods to configure the session factory properties.

Below is an example of a session factory that uses in-memory persistence and static key management.

SessionFactory sessionFactory = SessionFactory.newBuilder("some_product", "some_service")
    .withInMemoryMetastore() // in-memory metastore
    .withNeverExpiredCryptoPolicy()
    .withStaticKeyManagementService("thisIsAStaticMasterKeyForTesting") // hard-coded/static master key
    .build());

Step 2: Create a session

Use the factory to create a session.

Session<byte[], byte[]> sessionBytes = sessionFactory.getSessionBytes("shopper123");

The scope of a session is limited to a partition id, i.e. every partition id should have its own session. Also note that a payload encrypted using some partition id, cannot be decrypted using a different one.

Step 3: Use the session to accomplish the cryptographic task

The SDK supports 2 usage patterns:

Encrypt / Decrypt

This usage style is similar to common encryption utilities where payloads are simply encrypted and decrypted, and it is completely up to the calling application for storage responsibility.

String originalPayloadString = "mysupersecretpayload";

// encrypt the payload
byte[] dataRowRecordBytes = sessionBytes.encrypt(originalPayloadString.getBytes(StandardCharsets.UTF_8));

// decrypt the payload
String decryptedPayloadString = new String(sessionBytes.decrypt(dataRowRecordBytes), StandardCharsets.UTF_8);

Store / Load

This pattern uses a key-value/document storage model. A Session can accept a Persistence implementation and hooks into its load and store calls.

Example HashMap-backed Persistence implementation:

Persistence dataPersistence = new Persistence<JSONObject>() {

  Map<String, JSONObject> mapPersistence = new HashMap<>();

  @Override
  public Optional<JSONObject> load(String key) {
    return Optional.ofNullable(mapPersistence.get(key));
  }

  @Override
  public void store(String key, JSONObject value) {
    mapPersistence.put(key, value);
  }
};

Putting it all together, an example end-to-end use of the store and load calls:

// Encrypts the payload, stores it in the dataPersistence and returns a look up key
String persistenceKey = sessionJson.store(originalPayload.toJsonObject(), dataPersistence);

// Uses the persistenceKey to look-up the payload in the dataPersistence, decrypts the payload if any and then returns it
Optional<JSONObject> payload = sessionJson.load(persistenceKey, dataPersistence);

Sample Applications

The samples directory includes sample applications that demonstrate use of Asherah SDK using various languages and platforms.

Further Reading

• Design And Architecture
• System Requirements
• Key Management Service
• Metastore
• Key Caching
• Code Structure
• SDK Internals
• Testing Approach
• FAQ

Supported Languages

• Java
• .NET
• Go
• Service Layer (gRPC)

Feature Support

Feature	Java	.NET	Go
AWS KMS Support	Yes	Yes	Yes
RDBMS Metastore	Yes	Yes	Yes
DynamoDB Metastore	Yes	Yes	Yes
Session caching	Yes	Yes	Yes
Encrypt/Decrypt pattern	Yes	Yes	Yes
Store/Load pattern.	Yes	Yes	Yes

Contributing

All contributors and contributions are welcome! Please see our contributing docs for more information.