Util::Lookup

This repository contains the code for the attack on OpenSSL's base64 decoding routine used in decoding RSA keys.

Publication

This work will appear in the proceedings of the 2021 ACM SIGSAC Conference on Computer and Communications Security. A copy of the paper can be found on arXiv.

@inproceedings{sieckberndt2021utillookup,  
    title     = {{Util::Lookup}: Exploiting key decoding in cryptographic libraries},  
    author    = {Sieck, Florian and Berndt, Sebastian and Wichelmann, Jan and Eisenbarth, Thomas},  
    booktitle = {Proceedings of the 2021 ACM SIGSAC Conference on Computer and Communications Security},  
    publisher = {{ACM}},  
    month     = Nov,  
    year      = 2021,  
}

Requirements and how to run

This code was run and tested with Ubuntu 20.04.

System config

Kernel boot config

GRUB_CMDLINE_LINUX_DEFAULT="nox2apic iomem=relaxed no_timer_check isolcpus=0,1 processor.max_cstate=0 intel_idle.max_cstate=0"

This configures the apic timer into the legacy mode, relaxes a few checks and disables dynamic scheduling for cores 0 and 1. Furthermore, the C-State should be restricted to C0 with the last two parameters.

Maximal C-State can be checked via:

$ cat /sys/module/intel_idle/parameters/max_cstate

P-States are disabled via the Bios config

In the Bios we disabled:

• Intel TurboBoost
• SpeedStep

Furthermore the CPU Frequency is locked

This is done by using the cpupower tool from userspace:

$ sudo cpupower frequency-set -g performance
$ # Check whether the frequency is already fixed, otherwise try to fix it to the base frequency manually:
$ # BASE_FREQUENCY has to be set / looked up before hand
$ sudo cpupower frequency-set -f ${BASE_FREQUENCY}GHz

Currenty core frequency can be checked with:

$ cat /proc/cpuinfo | grep MHz

Intel SGX

Install the Intel SGX driver in version 2.11.

SGX-Step

Finally, SGX-Step has to be installed and configured properly (required version is included as a submodule) and the patched SGX-Step SGX-SDK must be sourced and the SGX-Step kernel module loaded. Please refer to the SGX-Step manual.

Additionally, it is important to use SGX-Step's bench app (nop slides) to determine the APIC Timer interupt interval and configure it such that single stepping works on the machine in use (see SGX-Step README).

Building and Running

Steps:

0. Source the SGX SDK's environment script and run the local_setup.sh script (you might need to update the latter to your needs)
1. Adjust build for either using mitigations or not (Currently configured to use LVI LOAD level mitigation)
2. Build : $ cd ./prime_n_probe && make all MITIGATION-CVE-2020-0551=LOAD
3. Update binary offsets: Use objdump to find the binary offsets (in encl.so) of the lookup table data_ascii2bin (look e.g. for '38393A' and identify the array's start address) and functions <evp_decodeblock_int>, <EVP_DecodeUpdate> (here we need the address of the inlined decodeblock, look for three successive 'shl') and update the variables offset_lt (address lookup table), offset_decodeblock_adrs, offset_decodeblock_adrs_inline
4. Build again (see 2.)
5. Run: $ cd ./prime_n_probe && sudo LD_LIBRARY_PATH=../sgx-step/sdk/intel-sdk/linux-sgx/psw/urts/linux ./pp_lookup
6. Evaluate:
   1. Set number of slices in prime_n_probe/parser/parser.py according to the number of slices of your L3 cache
   2. Analyze all traces with $ python3 parser/parser.py log.out > parsed_result.out
   3. Repeat this step (maybe in a loop) to gather data for more than just one run and move all parsed results to a folder
   4. Run $ python3 analyze_results.py --folder results/parsed/

Key reconstruction

There is another repository which includes all our code for reconstructing the key from the leakage obtained in this attack.