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sgxfun

Utilities and documentation for Intel SGX.

  • Our paper

  • parse_enclave.py takes an enclave in binary form and extracts some metadata

  • parse_quote.py takes a quote in binary form and extracts its fields

  • parse_sealed.py takes a sealed blob of data and extracts its fields

  • GETQUOTE.md documents the quote format and cryptographic scheme behind, as implemented in the quoting enclave

Extracting information from an enclave

Usage: ./parse_enclave.py <enclave.signed.dll|enclave.signed.so>

SIGSTRUCT

SIGSTRUCT contains information about the enclave, including hash and signature, and most of its fields are cryptographically signed, thus avoiding a modified enclave to run on the platform.

The data structure is contained on signed enclave files (.dll and .so), and it's also used on runtime when initializing the enclave.

The parse_enclave.py output, when SIGSTRUCT is found, can reveal some useful data about the enclave:

  • VENDOR: 00008086h for Intel enclaves; 00000000h otherwise
  • MODULUS: The signer's public key
  • ENCLAVEHASH: MRENCLAVE of this enclave (includes not only the raw data, but a log of the enclave memory initialization process)
  • ATTRIBUTES: Enclave attributes that must be set
  • ATTRIBUTEMASK: Filter mask for ATTRIBUTES; bits zeroed here are enforced to be disabled during initialization.
  • ISVPRODID and ISVSVN: Allows to identify different security releases (ISVSVN) of the same product (ISVPRODID) from the same vendor.

For additional information, check SIGSTRUCT entry on the Intel SGX Programming Reference (Section 2.13).

Signature Verification

RSA parameters from SIGSTRUCT are verified at the beginning of parse_enclave.py execution.

ECALLs

ECALLs are the enclave entry points to the trusted zone: only these memory positions can be called from the outside. In practice, they behave as functions that can be invoked, receiving parameters and returning values, as any other function.

Understading where are these ECALLs located and what's their functionality is essential when reversing an enclave, as they will reveal the attack surface and the functionality exposed. Special attention must be paid to debug and obsolete interfaces that could be present by mistake.

At the moment, the ECALLs table is located through a small set of heuristics not 100% reliable (known to fail in latest release of the PSW, 1.6 at the moment of writing).

When found, the table looks like this:

# ECALLs table found at 0x7b580
                   0    vaddr: 0x670
                   1    vaddr: 0xd20

The example contains the entry points found at a sample enclave and reveals to entry points at Virtual Addresses 0x0670 and 0x0d20. These entry points can serve as the beginning of a reverse engineering session.

Extracting information from a quote

Usage: ./parse_quote.py <quote.bin>

Quotes are sent from the enclave to the software vendor server while the remote attestation process. Together with the signature, they include a report of the enclave running.

When intercepted, they can provide information about what enclave is running, which key was used to sign it or wether they are running in debug mode or not. They also carry the security revisions of the platform (CPUSVN and ISVSVN).

Extracting information from a sealed blob

Usage: ./parse_sealed.py <sealed.bin>

Sealing policy

The policy used to derive the sealing key determines which enclaves will be able to decrypt the blob. Two possible values:

  • MRENCLAVE: The key derivation function includes the hash of the enclave, and only the enclave who performed the operation, running on the same machine and signed by the same signer, can unseal it.

  • MRSIGNER: The key derivation function does not includes the hash of the enclave. Other enclaves, running on the same machine and signed by the same signer, can unseal it.

Additional authenticated data

Sealed blobs can carry additional authenticated data, that is not encrypted but only authenticated. This piece of data can reveal useful information regarding the sealed blob.

Copyright (c) 2016, Nagravision S.A.

Code under GPLv3