Opaque for Apache Spark

How to build and test Opaque:

Install dependencies:

sudo yum -y install gcc48.x86_64 gcc48-c++.x86_64
sudo yum -y update binutils
# For fetching benchmark data
yum -y --enablerepo epel install s3cmd
s3cmd --configure

Install the Linux SGX SDK with C++11 support:

git clone https://github.com/ankurdave/linux-sgx -b c++11
cd linux-sgx
./download_prebuilt.sh
make sdk_install_pkg
# Installer will prompt for install path, which can be user-local
./linux/installer/bin/sgx_linux_x64_sdk_*.bin

On the master, generate a keypair using OpenSSL for remote attestation. Only the NIST p-256 curve is supported.
```
cd ${OPAQUE_HOME}
openssl ecparam -name prime256v1 -genkey -noout -out private_key.pem
```

Fetch the benchmark data:

cd ${OPAQUE_HOME}
DATA_DIR=... REPO_DIR=${OPAQUE_HOME} ./data/fetch-data.sh

Set the following environment variables in ${SPARK_HOME}/conf/spark-env.sh and in your shell:

export SGX_SDK=.../sgxsdk # from step 2
export SPARKSGX_DATA_DIR=... # from step 4
export LIBSGXENCLAVE_PATH=${OPAQUE_HOME}/libSGXEnclave.so
export LIBENCLAVESIGNED_PATH=${OPAQUE_HOME}/enclave.signed.so
export LIBSGX_SP_PATH=${OPAQUE_HOME}/libservice_provider.so
export PRIVATE_KEY_PATH=${OPAQUE_HOME}/private_key.pem

Run the Opaque tests:
```
cd ${OPAQUE_HOME}
build/sbt test
```