attested_tls

Prerequisites

The audience is assumed to be familiar: What is an Attested TLS channel

The Attested TLS sample

It has the following properties:

• Demonstrates attested TLS feature
  • between two enclaves
  • between an enclave application and a non enclave application
• Use of MbedTLS/OpenSSL crypto libraries within enclaves for TLS
• Select between MbedTLS and OpenSSL crypto libraries by setting an environment variable OE_CRYPTO_LIB to mbedtls or openssl at build time (Note that OE_CRYPTO_LIB is case sensitive).
• If the OE_CRYPTO_LIB not set, Mbed TLS will be used by default (see Makefile and CMakeLists.txt).
• Configure both the server and the client with recommended cipher suites and elliptic curves (refer to the section for more details).
• Use of following Enclave APIs
  • oe_get_attestation_certificate_with_evidence
  • oe_free_attestation_certificate
  • oe_verify_attestation_certificate_with_evidence

Note: Currently this sample only works on SGX-FLC systems. The underlying SGX library support for end-to-end remote attestation is required but available only on SGX-FLC system. There is no plan to back port those libraries to either SGX1 system or software emulator.

Overall Sample Configuration

In first part of this sample, there are two enclave applications in this sample: one for hosting an TLS client inside an enclave and the other one for an TLS server.

In the 2nd part of this sample, there is one regular application functioning as a non-enclave TLS client and an enclave application instantiating an enclave which hosts an TLS server.

Note: Both of them can run on the same machine or separate machines.

Server application

• Host part (tls_server_host)
  • Instantiate an enclave before transitioning the control into the enclave via an ecall.
• Enclave (tls_server_enclave.signed)
  • Call oe_get_attestation_certificate_with_evidence to generate an certificate
  • Use the MbedTLS/OpenSSL API to configure a TLS server using the generated certificate
  • Launch a TLS server and wait for client connection request
  • Read client payload and reply with server payload
• How to launch a server instance

../server/host/tls_server_host ../server/enc/tls_server_enc.signed -port:12341

Enclave Client application

• Host part (tls_client_host)
  • Instantiate an enclave before transitioning the control into the enclave via an ecall.
• Enclave (tls_client_enclave.signed)
  • Call oe_get_attestation_certificate_with_evidence to generate an certificate
  • Use MbedTLS/OpenSSL API to configure an TLS client after configuring above certificate as the client's certificate
  • Launch a TLS client and connect to the server
  • Send client payload and wait for server's payload
• How to launch a client instance

../client/host/tls_client_host ../client/enc/tls_client_enclave.signed -server:localhost -port:12341

Non-enclave Client application

• When used in this scenario, this non-enclave client is assumed to be a trusted party holding secrets and only shares it with the server after the server is validated
• Connect to server port via socket
• Use OpenSSL API to configure a TLS client
• Call oe_verify_attestation_certificate_with_evidence to validate server's certificate
• Send client payload and wait for server's payload

../client/tls_non_enc_client -server:localhost -port:12341

Build and run

Linux

CMake

• Use Mbed TLS

  mkdir build
  cd build
  cmake -DOE_CRYPTO_LIB=mbedtls ..
  make
  make run

• Use OpenSSL

  mkdir build
  cd build
  cmake -DOE_CRYPTO_LIB=openssl ..
  make
  make run

GNU Make

• Use Mbed TLS

  make OE_CRYPTO_LIB=mbedtls build
  make run

• Use OpenSSL

  make OE_CRYPTO_LIB=openssl build
  make run

Windows

CMake

• Use Mbed TLS

  mkdir build
  cd build
  cmake -G Ninja -DOE_CRYPTO_LIB=mbedtls ..
  ninja
  ninja run

• Use OpenSSL

  mkdir build
  cd build
  cmake -G Ninja -DOE_CRYPTO_LIB=openssl ..
  ninja
  ninja run

Note: This sample has a dependency on the socket support added in the OE SDK v0.6.0 release, so it needs to be linked against the liboehostsock and libhostresolver libraries. For more details, see Using the Open Enclave I/O subsystem.

Running attested TLS server in loop

By default the server exits after completing a TLS session with a client. -server-in-loop run-time option changes this behavior to allow the TLS server to handle multiple client requests.

On Linux:

./server/host/tls_server_host ./server/enc/tls_server_enc.signed -port:12341 -server-in-loop
or
make run-server-in-loop

On Windows after building the sample as described in the README file:

.\server\host\tls_server_host .\server\enc\tls_server_enc.signed -port:12341 -server-in-loop

Recommended TLS configurations when using OpenSSL

It is strongly recommended that developers configure OpenSSL to restrict the TLS versions, cipher suites and elliptic curves to be used for TLS connections to enclave:

• TLS protocol versions
  • TLS 1.2
  • TLS 1.3
• TLS 1.3 cipher suites (in the exact order)
  • TLS13-AES-256-GCM-SHA384
  • TLS13-AES-128-GCM-SHA256
• TLS 1.2 cipher suites (in the exact order)
  • ECDHE-ECDSA-AES128-GCM-SHA256
  • ECDHE-ECDSA-AES256-GCM-SHA384
  • ECDHE-RSA-"AES128-GCM-SHA256
  • ECDHE-RSA-AES256-GCM-SHA384
  • ECDHE-ECDSA-AES128-SHA256
  • ECDHE-ECDSA-AES256-SHA384
  • ECDHE-RSA-AES128-SHA256
  • ECDHE-RSA-AES256-SHA384
• Elliptic curves
  • P-521
  • P-384
  • P-256

This sample illustrates how to use initalize_ssl_context() to configure the SSL_CTX as suggested in both the server and the client modules.