Category: systems

Javascript Timing and Meltdown

In response to meltdown/spectre side-channel vulnerabilities, which are based on fine grained observation of the CPU to infer cache state of an adjacent process or VM, a mitigration response by browsers was the reduction of the time resolution of various time apis, especially in javascript.

The authors responded with alternative sources of finding fine grained timing, available to browsers. An interpolation method allows obtaining of a fine resolution of 15 μs, from a timer that is rounded down to multiples of 100 ms.

The javascript  high resolution time api is still widely available and described at with a reference to previous work on cache attacks in Practical cache attacks in JS

A meltdown PoC is at, to test the timing attack in its own process. The instruction RDTSC returns the Time Stamp Counter (TSC), a 64-bit register that counts the number of cycles since reset, and so has a resolution of 0.5ns on a 2GHz CPU.

int main() {
 unsigned long i;
 i = __rdtsc();
 printf("%lld\n", i);

Ethereum Security and the DAO Solidity Attack

The basics of Ethereum are described in the Gavin Wood paper. A list of keywords in Solidity are described in this file from its source, which includes “address”, “contract”, “event”, “mapping” and “wei” ( 1 Eth= 10^18 Wei). This list does not include “gas”, which is a mechanism described in Wood’s paper to combat abuse. Interestingly the paper says “The first example of utilising the proof-of-work as a strong economic signal to secure a currency was by Vishnumurthy et al [2003]”, aka the Karma paper.

The karma paper talks about solving a cryptographic puzzle as enabling one to join the network and be assigned a bank set: “the node certifies that it completed this computation by encrypting challenges provided by its bank-set nodes with its private key. Thus each node is assigned an id beyond its immediate control, and acquires a public-private key pair that can be used in later stages of the protocol without having to rely on a public-key infrastructure”. Crypto puzzles for diverseproblems have been proposed before, a survey and comparison is at

The DAO attack had 3 components, a hacker, a malicious contract and a vulnerable contract. The malicious contract is used to withdraw funds from the vulnerable contract so that it does not get a chance to decrement its balance. Oddly enough the gas mechanism which is supposed to limit computation did not kick in to stop this repeated remittance.

A few weeks before the DAO attack someone had pointed out to me that security of solidity was a bit of an open problem. My feeling was contracts should be layered above the value exchange mechanism, not built into it. Bitcoin based protocols with the simpler OP_RETURN semantics appeared more solid. Later around October’16 at an Ethereum meetup, Fred Ehrsam made the comment that most new projects would be using Ethereum instead of bitcoin. But Bitcoin meetups had more real-world use cases being discussed. The technical limitations exist, which are being addressed by forks such as SegWit2x this November.  Today saw a number of interesting proposals with Ethereum, including Dharma, DataWaller and BloomIDs. Security would be a continuing  concern with the expanding scope of such projects.

NVidia Tiny Linux Kernel and TrustZone

The NVidia Tiny Linux Kernel (TLK), is 23K lines of BSD licensed code, which supports multi-threading, IPC and thread scheduling and implements TrustZone features of a Trusted Execution Environment (TEE). It is based on the Little Kernel for embedded devices.

The TEE is an isolated environment that runs in parallel with an operating system, providing security. It is more secure than an OS and offers a higher level of functionality than a SE, using a hybrid approach that utilizes both hardware and software to protect data. Trusted applications running in a TEE have access to the full power of a device’s main processor and memory, while hardware isolation protects these from user installed apps running in a main operating system. Software and cryptographic isolation inside the TEE protect the trusted applications contained within from each other. A paper describing the separation with alternatives for virtualizing the TEE appeared at

TrustZone was developed by Trusted Foundations Software which was acquired by Gemalto. Giesecke & Devrient developed a rival implementation named Mobicore. In April 2012 ARM, Gemalto and Giesecke & Devrient combined their TrustZone portfolios into a joint venture Trustonic, which was the first to qualify a GlobalPlatform-compliant TEE product in 2013.

A comparison with other hardware based security technologies is found here. Whereas a TPM is exclusively for security functions and does not have access to the CPU,  the TEE does have such access.

Attacks against TrustZone on Android are described in this blackhat talk. With a TEE exploit,  “avc_has_perm” can be modified to bypass SELinux for Android. By the way, Access Vectors in SELinux are described in this wonderful link. “avc_has_perm” is a function to check the AccessVectors allows permission.

Embedded Neural Nets

A key problem for embedded neural networks is reduction of size and power consumption.

The hardware on which the neural net runs on can be a dedicated chip, an FPGA, a GPU or a CPU. Each of these consumes about 10x the power of the previous choice. But in terms of upfront cost, the dedicated chip costs the highest, the CPU the lowest. An NVidia whitepaper compares GPU with CPU on speed and power consumption. (It discusses key  neural networks like AlexNet. The AlexNet was a breakthrough in 2012 showing a neural network to be superior to other image recognition approaches by a wide margin).

Reducing the size of the neural network also reduces its power consumption. For NN size reduction, pruning of the weak connections in the net was proposed in “Learning both Weights and Connections for Efficient Neural Networks” by Song Han and team at NVidia and Stanford. This achieved a roughly 10x reduction in network size without loss of accuracy. Further work in “Deep Compression” achieved a 35x reduction.

Today I attended a talk on SqueezeNet by Forrest Iandola. His team at Berkeley modified (squeezed) the original architecture, then applied the Deep Compression technique above to achieve a 461x size reduction over the original, to 0.5Mb. This makes it feasible for mobile applications. This paper also references the V.Badrinarayan’s work on SegNet – a different NN architecture, discussed in a talk earlier this year.

The Nervana acquisition by Intel earlier this year was for a low power GPU like SOC chip with very high memory bandwidth.

Spark, Storm, Ayasdi, Hadoop

The huge amount of data that IOT systems will generate will call for analyses of different types. A brief review of some systems and what they are used for.

Apache Spark: Uses distributed memory abstractions for primarily in-memory processing. Built with Scala. Useful for finding data clusters and for detecting statistical anomalies by looking for distance from the cluster. Comes with a machine learning system on top. Does not come with its own file system (use nfs/hdfs). Useful for complex processing, where state needs to be maintained in the event stream for correlations. Described as ‘batch processing with micro-streaming analysis’, but looks headed to cover streaming analyses as well.

Apache Storm: Real-time Streaming data analysis. Developed at Twitter, written in Clojure. Unlike Hadoop which has two layers (map, reduce), Storm can have N layers and a flexible topology consisting of Spouts (data source units) and Bolts (data processing units). Storm has been superceded by Heron in terms of performance. IBM Streams is a commercial offering also for stream processing..

Ayasdi: Topological data processing allows one to discover what interesting features of the data are, without knowing what to look for in advance. This is in contrast to most systems where one needs to know what one is looking for. Claims insight discovery.

Hadoop: Used for batch processing of a large amounts of data, using map/reduce primitives. Comes with HDFS. Cloudera (and others) have made significant improvements to it with an interactive SQL interface and usability improvements for BI (Impala).

InfluxDB: Time-series db for events and metrics. Optimized for writes and claims to scale to IOT workloads.

ZooKeeper: A coordination service for distributed applications.

Amazon S2N and OpenSSL

In the last few years a number of OpenSSL vulnerabilities have come to light.  Heartbleed was a critical one which was exploited in the field. It basically allowed a client to send a malicious heartbeat to the server and get back chunks of server memory – which can contain passwords. It was estimated that two thirds of the servers in the world had the vulnerability. The fix was to upgrade OpenSSL, revoke existing server certs and request new SSL server certs.

Heartbleed previously triggered OpenBSD to fork OpenSSL to LibreSSL and Google to fork OpenSSL to BoringSSL.

Amazon S2N is a TLS/SSL implementation that is 6000 lines of code – so it is small, compact, fast and its correctness can be more easily verified. It uses only crypto functions from openssl and reimplements the SSL layer. This is a healthy direction for IOT and for certification of SSL, for example FIPS. S2N is short for Signal to Noise.

A timing attack was recently identified against it and has since been mitigated.

Note that two factor auth solutions would actually solve the problem presented by Heartbleed. There are several solutions in this area – Authy, Clef, Google Authenticator, Duo, Okta, Oracle Authenticator, ..

Docker Container Security

A block diagram of docker is below and a description of docker daemon is here. The docker client commands talk to the docker-daemon to start one of the containers in the docker registry, or to start a process described in the command line as a new docker container. Docker provides a simple interface to linux container technology which is a lightweight VM.


A few problems with this. Who has access to the docker-daemon to control the containers ? How is integrity of the containers ensured ? How is the host protected from the code running in the containers ?

Docker recently announced a few security features in Nov DockerCon

  • to lock down the container in a registry with the container image signed with a key from hardware device Yubikey; see here for a description of original issue where image checksums were not verified by docker daemon
  • to scan the official container images for vulnerabilities
  • to run containers with a userlevel namespace instead of one that allows root access to the host. This protects the host OS as explained here. The userlevel namespace feature has been available in LXC for over an year, but not in docker.

For access control to the docker daemon there is activity with a design doc here.

Twistlock is a container security and monitoring tool that attempts a comprehensive approach – access control to the containers, runtime scanning of files for malware signatures, vulnerability scanning, looking at network packets, so on. A recent meetup on Dec 1 discussed this product. It features integration with Kerberos and LDAP.

In terms of the kernel,  processes from all containers share the same kernel, the same networking layer. So what’s the level of isolation provided to container processes. This depends on vulnerabilities in the processes themselves – how many ports are open, whether injection attacks are possible etc. If two containers are running processes and a process from the one attacks a process from another – for example memory scraping, then Twistlock can detect it only if it can identify the offending process as malware using signature matching.

A Dockerfile is used to specify a container image using commands to spec the base os, rpms, utilities and scripts. USER specifies the userid under which the following RUN, CMD or ENTRYPOINT instruction run. EXPOSE specs a port to be opened for external access. A docker image is built from the dockerfile and contains the actual bits needed for the container to run. The image can be loaded directly or pushed to a docker registry from  which it can be pulled to clients.