Supported functionalities#

This section lists Opaque’s supported functionalities, which is a subset of that of Spark SQL. The syntax for these functionalities is the same as Spark SQL – Opaque simply replaces the execution to work with encrypted data.

SQL interface#

Data types#

Out of the existing Spark SQL types, Opaque supports

  • All numeric types. DecimalType is supported via conversion into FloatType

  • StringType

  • BinaryType

  • BooleanType

  • TimestampTime, DateType

  • ArrayType, MapType

Functions#

We currently support a subset of the Spark SQL functions, including both scalar and aggregate-like functions.

  • Scalar functions: case, cast, concat, contains, if, in, like, substring, upper

  • Aggregate functions: average, count, first, last, max, min, sum

UDFs are not supported directly, but one can extend Opaque with additional functions by writing it in C++.

Operators#

Opaque supports the core SQL operators:

  • Projection (e.g., SELECT statements)

  • Filter

  • Global aggregation and grouping aggregation

  • Order by, sort by

  • All join types except: cross join, full outer join, existence join

  • Limit

DataFrame interface#

Because Opaque SQL only replaces physical operators to work with encrypted data, the DataFrame interface is exactly the same as Spark’s both for Scala and Python. Opaque SQL is still a work in progress, so not all of these functionalities are currently implemented. See below for a complete list in Scala.

Supported operations#

Typed transformations#

Unsupported operations#

User-Defined Functions (UDFs)#

To run a Spark SQL UDF within Opaque enclaves, first name it explicitly and define it in Scala, then reimplement it in C++ against Opaque’s serialized row representation.

For example, suppose we wish to implement a UDF called dot, which computes the dot product of two double arrays (Array[Double]). We [define it in Scala](src/main/scala/edu/berkeley/cs/rise/opaque/expressions/DotProduct.scala) in terms of the Breeze linear algebra library’s implementation. We can then use it in a DataFrame query, such as logistic regression.

Now we can port this UDF to Opaque as follows:

  1. Define a corresponding expression using Opaque’s expression serialization format by adding the following to [Expr.fbs](src/flatbuffers/Expr.fbs), which indicates that a DotProduct expression takes two inputs (the two double arrays):

    table DotProduct {
  left:Expr;
  right:Expr;
}

    In the same file, add DotProduct to the list of expressions in ExprUnion.

  2. Implement the serialization logic from the Scala DotProduct UDF to the Opaque expression that we just defined. In Utils.flatbuffersSerializeExpression (from Utils.scala), add a case for DotProduct as follows:

    case (DotProduct(left, right), Seq(leftOffset, rightOffset)) =>
  tuix.Expr.createExpr(
    builder,
    tuix.ExprUnion.DotProduct,
    tuix.DotProduct.createDotProduct(
      builder, leftOffset, rightOffset))

  3. Finally, implement the UDF in C++. In FlatbuffersExpressionEvaluator#eval_helper (from expression_evaluation.h), add a case for tuix::ExprUnion_DotProduct. Within that case, cast the expression to a tuix::DotProduct, recursively evaluate the left and right children, perform the dot product computation on them, and construct a DoubleField containing the result.