Technology

What is Attribute-Based Encryption (ABE)?

Encryption is a method of encoding data that protects the confidentiality of its contents from unauthorized attackers. Traditionally, encryption was viewed as a tool to enable secure communication between a sender and a targeted recipient of information. For example, one might wish to store a message such that it can only be decrypted by the user bob@xyz.org.

Attribute-Based Encryption is a more expansive type of encryption that allows for flexible policy-based access controls that are cryptographically (that is, mathematically) enforced. Instead of encrypting data to a single user, it is now possible to encrypt it so that the data can be decrypted by anyone with credentials satisfying an arbitrary attribute-based access control policy.

In our ABE solutions, any string can serve as an attribute. In addition, attributes can be numeric values and policies can contain ranges over these values. The set of attributes used will depend on the designated application.

In order to understand the capabilities of ABE, it helps to organize them logically into three variants.

  • Content-based Access Control is for granting selective access later (e.g., cloud, email, big data, subpoenas).
  • In an ABE system for content-based access control, attributes are associated with a ciphertext and the private key is associated with a policy over these attributes. (In the academic literature, this variant is sometimes referred to as "Key-Policy" ABE). For example, a company could automatically encrypt all of its emails with the attributes being some (or all) of the 75 fields in Mail headers and then later the company can distribute a key to an analyst that allows for decryption of all emails that meet the policy of 'To:engineering@corporation.com' OR (subject contains 'cascade project' AND sent between 'Dec 21, 2017' and 'Jan 10, 2018'.

  • Role-based Access Control is for policies known at the time of encryption (e.g., classified documents, medical records).
  • An ABE system for role-based access control "flips" the semantics of content-based access control. In such a system, attributes are associated with a private key and a policy (or boolean formula) is associated with the ciphertext. Here the attributes are often be associated with the credentials of a private key holder. (In academic literature this variant is sometimes referred to as "Ciphertext-Policy" ABE.) For instance, one could restrict a ciphertext only to female employees who have been with the company since 2012 and worked on the "HALE" software project.

  • Multi-authority Role-based Access Control is for operating across organizational boundaries.
  • One issue with role-based access control is that in many applications you may need to write access control policies that span across different administrative boundaries. In standard ABE, there is one authority that hands out private keys. However, in some applications, it is natural for different authorities to manage different attributes. A multi-authority ABE system allows one to associate a ciphertext with a policy written across attributes issued by different authorities. These authorities can operate independently and do not have to coordinate (or even be aware of) each other.

    For instance, the government might certify the attributes in a person's driver's license (such as age), while a credit score company could distribute credentials about a user's credit score and an employer could distribute credentials about its employees. With this type of ABE, one can now send out a special offer readable by anyone over age 50 with a strong credit score and a job at a local employer.

Why use Attribute-Based Encryption?

Attribute-Based Encryption (ABE) can do all that regular public key encryption can do, but also much more. It allows an organization to enforce fine-grained access controls in math, without the need for a complex infrastructure and with the ability to operate offline. It is a novel way of marrying access controls and encryption that makes sharing sensitive data easier and more secure.

What are the applications of ABE?

Any application that has sensitive data-at-rest could benefit from ABE. Selected application areas include:

  • Cloud
  • Mobile
  • Email
  • Military
  • Healthcare
  • Financial
  • Databases
  • Vehicular Communications
  • Corporate data storage
  • Personal data storage