OpenSSH SK API implemented with Intel SGX

Treat the Intel SGX as a FIDO-like authenticator: Generate private ED25519-SK keys on a stateless SGX enclave. Private keys are sealed by the enclave and stored in the key handle of the ED25519-SK key. Only the enclave can un-seal such a private key.

The file sk-sgx.c implements the SSH_SK_PROVIDER for OpenSSH, enclave.c the matching SGX enclave. The interface between provider and enclave is specified in sk.edl.

This code can be used to protect private SSH host keys, for example. If SGX is supported by the virtual machine, then the private key will also be hidden from the cloud provider.

Install Ubuntu 18.04

See https://github.com/openenclave/openenclave/blob/master/docs/GettingStartedDocs/HyperVLinuxVMSetup.md for running Ubuntu with SGX on HyperV.

Install SDK

• https://01.org/intel-software-guard-extensions/downloads
• https://download.01.org/intel-sgx/sgx-linux/2.7.1/distro/ubuntu18.04-server/
• https://download.01.org/intel-sgx/sgx-linux/2.7.1/docs/Intel_SGX_Installation_Guide_Linux_2.7.1_Open_Source.pdf

Build provider and enclave

% source /home/ubuntu/sgxsdk/environment
% make

or

% make SK_DEBUG=1

Use the resulting sk-sgx.so library as the SSH_SK_PROVIDER. It will execute enclave.signed.so in the SGX enclave.

% SSH_SK_PROVIDER=./sk-sgx.so /home/ubuntu/ssh/bin/ssh-keygen -t ed25519-sk
% SSH_SK_PROVIDER=./sk-sgx.so /home/ubuntu/ssh/bin/ssh host

If you don't have SGX hardware, you can use the simulator:

% make SGX_MODE=SIM

If you want to use run sk-sgx standalone without OpenSSH:

% make SGX_MODE=SIM SK_DEBUG=1 TEST=1
% ./sk-sgx.so

WARNING

If you sign enclave.so with a different private.pem, then the MRSIGNER measurement changes and the private keys can no longer be decryped.

Notes

• SGX intro: https://blog.quarkslab.com/overview-of-intel-sgx-part-1-sgx-internals.html
• SGX details: https://eprint.iacr.org/2016/086.pdf
• emulated instructions in SDK: sdk/simulation/tinst/t_instructions.cpp
• Foreshadow (spectre): https://www.usenix.org/system/files/conference/usenixsecurity18/sec18-van_bulck.pdf
• SCONE (container): https://www.usenix.org/system/files/conference/osdi16/osdi16-arnautov.pdf

-m