In previous articles I’ve explained how to use traditional SSH keys and why connecting to a wrong server could expose your password. I was reminded of a newer form of authentication supported by OpenSSH; CA keys. The CA key model is closer to how SSL certs work; you have an authority that is trusted by the servers and clients, and a set of signed keys. Creating the CA key Creating a certificate authority key is pretty much the same as creating any other key
Modern web browsers have a number of settings to help protect your site from attack. You turn them on by use of various header lines in your HTTP responses. Now when I first read about them I thought they were not useful; a basic rule for client-server computing is “don’t trust the client”. An attacker can bypass any rules you try to enforce client side. But then I read what they do and realised that they are primary to help protect the client and, as a consequence, protect your site from being hijacked.
(Side note: in this post I’m going to use TLS and SSL interchangably. To all intents and purposes you can think of TLS as the successor to SSL; most libraries do both). You can think of security as a stack. Each layer of the stack needs to be secure in order for the whole thing to be secure. Or, alternatively, you can think of it as a chain; the whole thing is only as strong as the weakest link.
In my previous post I wrote about some automation of static and dynamic scanning as part of the software delivery pipeline. However nothing stays the same; we find new vulnerabilities or configurations are broken or stuff previously considered secure is now weak (64bit ciphers can be broken, for example). So as well as doing your scans during the development cycle we also need to do repeated scans of deployed infrastructure; espcially if it’s externally facing (but internal facing services may still be at risk from the tens of thousands of desktops in your organisation).
In many organisations an automated scan of an application is done before it’s allowed to “go live”, especially if the app is external facing. There are typically two types of scan: Static Scan Dynamic Scan Static scan A static scan is commonly a source code scan. It will analyse code for many common failure modes. If you’re writing C code then it’ll flag on common buffer overflow patterns.
In an earlier blog I wrote that SSH keys need to be managed. It’s important! In the comments I was asked about keytabs. I felt this such a good question that it deserved it’s own blog entry. The basics of Kerberos auth In essence, kerberos is a “ticket based” authentication scheme. You start by requesting a TGT (“Ticket granting ticket”). This, typically, is where you enter your password. This TGT is then used to request service tickets to access resources.
Over on the Unix/Linux Stackexchange someone asked if ssh’ing to the wrong machine could cause their password to be exposed. I answered “yes”… and was surprised to see the answer get over 140 upvotes. Demonstration So it seems as if there’s some interest in this. I decided to demonstrate this risk in a short practical session. Let’s start with a generic CentOS 7 install. It’s got nothing special on it.
What is a HSM? A HSM is a hardware device that can perform cryptographic functions in a “secure” manner. The idea is that you can load your private key into a HSM and be sure that it’s safe from theft. Anyone tries to physical access the device and it’ll wipe (or literally burn) the data. So encryption or signing of data can be trusted because only the HSM has the key needed to do the crypto.
SSH is probably the most common method of logging into Unix machines over a network connection. It has pretty much replaced the older telnet and rlogin protocols because it encrypts data over the network and has other “goodness”. However one of the “good” parts of ssh is probably the least well managed; ssh keys. What is an ssh key? When attempting to login to a server, ssh will attempt multiple different authenticators.
Something I’ve been pushing (and this is pretty much a truism amongst anyone who’s looked at “Cloud”) is the idea of automation. It doesn’t matter if you’re just treating the cloud as an outsourced datacenter or if you’re doing full 12-factor dynamically scalable apps. Automation is the key to consitency and control. So, ideally, this means your automation system is the “single point of truth” for your estate. Whether you use ansible or chef or (saints preserve us) cfengine, your configuration file explicitly defines your target state.
