Every Key-Value pair in Accumulo has its own security label, stored under the column visibility element of the key, which is used to determine whether a given user meets the security requirements to read the value. This enables data of various security levels to be stored within the same row, and users of varying degrees of access to query the same table, while preserving data confidentiality.

Writing labeled data

When writing data to Accumulo, users can specify a security label for each value by passing a ColumnVisibility to the Mutation.

try (BatchWriter writer = client.createBatchWriter("employees")) {
  Mutation mut = new Mutation("employee1");
  mut.at().family("pay").qualifier("salary").visibility("payroll").value("50000");
  mut.at().family("pay").qualifier("period").visibility("public").value("monthly");
  writer.addMutation(mut)
}

Security Label Expression Syntax

Security labels consist of a set of user-defined tokens that are required to read the value the label is associated with. The set of tokens required can be specified using syntax that supports logical AND & and OR | combinations of terms, as well as nesting groups () of terms together.

Each term is comprised of one to many alphanumeric characters, hyphens, underscores or periods. Optionally, each term may be wrapped in quotation marks which removes the restriction on valid characters. In quoted terms, quotation marks and backslash characters can be used as characters in the term by escaping them with a backslash.

For example, suppose within our organization we want to label our data values with security labels defined in terms of user roles. We might have tokens such as:

admin
audit
system

These can be specified alone or combined using logical operators:

// Users must have admin privileges
admin

// Users must have admin and audit privileges
admin&audit

// Users with either admin or audit privileges
admin|audit

// Users must have audit and one or both of admin or system
(admin|system)&audit

When both | and & operators are used, parentheses must be used to specify precedence of the operators.

Authorizations

When clients attempt to read data from Accumulo, any security labels present are examined against an Authorizations object passed by the client code when the Scanner or BatchScanner are created. If the Authorizations are determined to be insufficient to satisfy the security label, the value is suppressed from the set of results sent back to the client.

Authorizations are specified as a comma-separated list of tokens the user possesses:

// user possesses both admin and system level access
Authorizations auths = new Authorizations("admin","system");

Scanner s = client.createScanner("table", auths);

User Authorizations

Each Accumulo user has a set of associated security labels. To manipulate these in the Accumulo shell, use the setuaths and getauths commands. They can be retrieved and modified in Java using getUserAuthorizations and changeUserAuthorizations methods of SecurityOperations.

When a user creates a Scanner or BatchScanner, a set of Authorizations is passed. If the Authorizations passed to the scanner are not a subset of the user’s Authorizations, then an exception will be thrown.

To prevent users from writing data they can not read, add the visibility constraint to a table. Use the -evc option in the createtable shell command to enable this constraint. For existing tables, use the config command to enable the visibility constraint. Ensure the constraint number does not conflict with any existing constraints.

config -t table -s table.constraint.1=org.apache.accumulo.core.security.VisibilityConstraint

Any user with the alter table permission can add or remove this constraint. This constraint is not applied to bulk imported data, if this a concern then disable the bulk import permission.

Advanced Authorizations Handling

For applications serving many users, it is not expected that an Accumulo user will be created for each application user. In this case an Accumulo user with all authorizations needed by any of the application’s users must be created. To service queries, the application should create a scanner with the application user’s authorizations. These authorizations could be obtained from a trusted 3rd party.

Often production systems will integrate with Public-Key Infrastructure (PKI) and designate client code within the query layer to negotiate with PKI servers in order to authenticate users and retrieve their authorization tokens (credentials). This requires users to specify only the information necessary to authenticate themselves to the system. Once user identity is established, their credentials can be accessed by the client code and passed to Accumulo outside of the reach of the user.

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