SSL/TLS cipher suite selection and breakdown.

How do I know which cipher suites to select for my web server?

This is a common issue, sysadmins have their web servers up or vpn servers configured. However they are often using older SSL protocols and older cipher suites that are now vulnerable to attack in certain scenarios. We need to understand what a cipher suite is actually doing in order to select the correct ones.

For SSL/TLS connections a cipher suite is selected based on a number of tasks that it has to perform, the client uses a preferred cipher suite list and the server will normally honor this unless it also has a preferred list, set by the sysadmin.

Initial Key Exchange, the Asymmetric Encryption: This will most commonly be RSA, however the following are options; RSA ( Ron Rivest, Adi Shamir, and Leonard Adleman), DH (Diffie-Hellman) or  ECDH (Elliptic Curve Diffie-Hellman).
RSA key length should be 2048 bit minimum. ECDH and others should be an equal strength, note the ECDH key length will be significantly lower due to the way the algorithm works! The Asymmetric Encryption is only being used in the initial key exchange and for the session symmetric encryption key. The Asymmetric encryption method could be used for the data transfer however the computational power needed is far higher than the symmetric Encryption due to the key size.

Session data, the Symmetric Encryption: The most commonly used three ciphers we see in use being RC4, 3DES and AES, careful selection of ciphers is required here:

  • RC4 (Rivest Cipher 4) although used almost everywhere is now considered weak, and being phased out by Microsoft. This should be avoided.
  • 3Des (Triple Data Encryption Standard) uses DES and encrypts three times hence the ‘triple’. The original DES uses a weak key length and is considered weak.
  • AES (Advanced Encryption Standard) 128 bit block size using 128, 192 and 256 bit keys to encrypt data, is all good.

Many other options are available that are not so common include Blowfish, Twofish, Serpent etc. I won’t be going into the different ciphers here or the difference between Block (3DES+ AES) and Stream (RC4) on this page, I’ll save this for another blog.

Digital Signature – The digital signature is used to verify the server.

Integrity check – Here SHA-2 or SHA 256 (Secure Hash Algorithm) should be used. MD5 and SHA1 are being phased out due to weaknesses. SHA1 will still be seen on certificates however Google Chrome will now show a warning for this since October 2014. Microsoft has a deprecation policy indicating SHA1 issued certificates should not be used after 1/1/2017.

With all that being said, lets look at a typical cipher suite. Below is what you might commonly see in the likes of Firefox if you click on the padlock in the address bar and then click on more information.

Cipher suite in use in Firefox
Cipher suite in use in Firefox

Lets look at the cipher suite below for an example. We’ll break down the individual blocks to see what it actually all means.

TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256

TLS – The protocol in use
ECDHE – Elliptic Curve Diffie-Hellman key-exchange using ephemeral keys. More on ephemeral keys later, however this is what is going to give you that all important ‘Perfect Forward Secrecy’. Marked with the E at the front or behind for Ephemeral.
ECDSA – Elliptic Curve Digital Signature Algorithm, used to create the digital signature for authentication.
AES_128 – Advanced Encryption Standard 128 bit key size, used for the session encryption method for data.
GCM – Galois/Counter Mode an operation for block ciphers designed to provide both data authenticity (integrity) and confidentiality. GCMAC – provides authentication only.
SHA256 – Secure hashing Algorithm 256bit used for message integrity.

With the above knowledge and knowing the current vulnerabilities in SSL and TLS we can now make an informed decision and build the cipher suites we would like to use in Windows and Linux.

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Changing SSL TLS Cipher Suites in Windows and Linux

Changing SSL TLS cipher suites on Windows Server 2012 R2I have added a basic guide for changing SSL TLS cipher suites that Windows Server IIS and Linux Ubuntu Apache2 use. Allowing only secure ciphers to be negotiated between your web server and client is essential. This guide will go through how to change and select the different ciphers for both Windows server 2012 R2 and Ubuntu 14.04 in order to help mitigate some of the vulnerabilities in the SSL/TLS protocols.

Read further on the Resource page for changing SSL TLS Cipher Suites here.

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Linux Firewall

Linux FirewallCheck out the Linux Firewall mini setup guide which demonstrates the use of iptables in Linux. Here I demonstrate a few basic commands and rules and explained how we can allow and deny specific traffic on your Linux server. The scenario is for typical web server allowing only HTTP, HTTPS and SSH. Host based firewalls are often overlooked relying solely on perimeter defenses however are an important aspect of protecting your endpoint whether that is on a server or workstation. Iptables in built into Linux is a pretty capable command line based stateful firewall. Once you have the hang on the syntax it is fairly straightforward to implement and customize to your own requirements.

Linux Firewall iptables
Linux Firewall iptables

Click to check out the full Linux Firewall iptables mini guide here.

 

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Labs and Virtualization

Anybody that works in IT that really wants to progress will know and will have experienced the value of labs and virtualization. Being able to test an idea or for learning in a virtual lab, its essential whether it be in Linux or Windows. Being able to through up a webserver to test a setting or a domain controller to test a group policy. Whether its on a full blown ESXi deployment or just virtual box. The aim of this page is to go through some of the virtualization options that are available to the home user, and dig into the software and hardware that’s required. Check out the following page for some hint and tips: https://www.adamcouch.co.uk/labs-projects/labs-and-virtualization/

Labs and Virtualization The great hypervisor! take your pick.

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Advanced Persistent Threats

Advanced Persistent Threats are becoming an increasingly prevalent threat to organisations and the information they hold. Advanced Persistent Threats are a type of attack that are defined by the National Institute of Standards and Technology (2011) as being a highly sophisticated attack, well-orchestrated, well-funded and are targeted at specific organisations or people. These type of attacks seek to gain a foothold inside an organisation, remain undetected and over a specific time frame from Advanced Persistent Threats
hours to months laterally move across the network and exfiltrate data, the specific information assets they desire undetected, often more than once. This is as opposed to the more conventional opportunist attacker who isn’t interested in any particular target or any specific data. If the attacker doesn’t succeed the first time they will simply move onto the next weakest victim, these types of attack have often in the passed been used only to heighten the profile of a hacker. Attack vectors include Spear fishing attempts with either email content or attachments carrying the payload through to malware and more commonly malvertising.

Evidence of high profile targeted Advanced Persistent Threats are being reported in the press more than ever. Some examples of such being Target’s 2013 breach, Sony 2014 breach and more recently Ashley Madison 2015 this list goes on. Upholding the confidentiality, availability and integrity of information that these sites and companies hold is possible through the use of good IT Governance. With an effective and current Information Security Management System in place and utilizing good strong controls organisations can better protect themselves from Advanced Persistent Threats.

Ensuring user awareness training is provided. Ensuring the desktop is appropriately secured. Keeping software up to date. Ensuring strong Authentication mechanisms are in place. Ensuring Antivirus, Firewalls and Host Intrusion Detection/Prevention systems are appropriately configured and kept up to date are all only some of the controls that should be in place as a standard to help mitigate the risk.

All too often perimeter defenses are in place and appropriately secured from the outside, however from inside out, the desktop and the actual user are all attack vectors that are left open to threats.  The threat landscape is constantly evolving, we need to stay on top in order to try and evade APTs.

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Blocking Advertisements and Malvertising

This is an interesting topic, blocking advertisements for me is a must. I not only feel much safer, I know I am safer browsing pages on the net with an Ad Blocker, I personally use Ad Block Plus for Firefox. There has been lots of press regarding malvertising of late, Huffington Post and FHM being victim. IT governance are seen to be quoting RiskIQ figures from this years Blackhat conference of malvertising being up 80% from last year. The Malvertising that we are seeing across the net coming from bad ad companies are particularly dangerous not requiring interaction from users, simply visiting the site being enough to become infected with malware. IT Security folk often have very clean surfing habits, however average users that aren’t as aware browsing the net will be susceptible to downloading malware without them even knowing. The malvertising needs a vessel in order to carry itself over to the victims computer in order for it to be exploited, that usually being a vulnerability in flash or Java. Keep it up to date – better still if you can live without it, do so, or block it with a add-on like ‘no script‘ for Firefox.

I do however sympathise with sites that rely on advertising to stay on the net, I realise I’m not supporting my favorite sites by blocking their ads as they are not receiving revenue from the ad companies however I’m not willing to compromise my own security either.

One interesting idea being the Google Contributor Service where people pay to not see advertising on sites that use google ads, instead they see a banner thanking them for contributing. One idea that will remain in play is paying our favorite sites  for their content on a subscription basis.  It will be interesting to see how this problem unfolds itself, one thing is for sure the problem is increasing and as malvertising increases, so will the use of Ad blockers which will only concatenate the problem of content providers not getting paid!

What are your thoughts…

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Installing VirtualBox Guest Additions in Kali Linux v1.x

A brief summary of the commands needed to install VirtualBox Guest Additions in Kali Linux v1.x. Having the Guest Additions installed is very useful, being able to copy and paste text like bash lines like the below is extremely useful. There is also the extra screen options such as the transparency mode. Being able to copy files in and out of the system into the host is also very useful.

Linux headers need to be updated.

#apt-get update && apt-get install -y linux-headers-$(uname -r)

Copy the VBoxLinuxAdditions.run file to the Desktop.

Restart.

#cp /media/cdrom/VBoxLinuxAdditions.run /root/Desktop/
#cd /root/Desktop/

Make it executable:

#chmod 755 VBoxLinuxAdditions.run

Install it:

#./VBoxLinuxAdditions.run
kali Virtualbox
Installing VirtualBox Guest Additions on Kali Linux version 1.x

Reboot for a final time.

After it has successfully installed you will now be able to go full screen, add in file sharing options, copy and paste and clipboard functionality. Enjoy.

 

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Cisco ASA in GNS3

Having spent many hours over several days trying to get to a point were I could run a Cisco ASA in GNS3 in stable condition has proven to to be harder than first thought. However I now have a set of configuration options specific to the Cisco ASA to keep it running in a stable manner in GNS3. Check it out under my  Labs and Projects menu here, let me know your thoughts or any other better ways to achieve this.

Follow the link here to creating a Cisco ASA in GNS3 here : https://www.adamcouch.co.uk/labs-projects/cisco-asa-firewall-in-gns3/

Cisco ASA in GNS3

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Quick SSL Scan

OK so with a my new website up my first thought was ‘right lets secure it!’. Now if only more people thought this way surely we wouldn’t see half the info sec issues we see today. So I’m probably slightly biased on the subject being a Pentester. Not sure if biased or paranoid is better word.

I’m supposed to be on holiday in wales for the bank holiday however 8 hours into the site build and can’t help but think, security. A few tasks later and I navigate to Qualys, lets see where we currently stand, 10 minuets later and I’m building a Kali 2.0 virtual machine in Virtual Box on my laptop in the hopes of pentesting it over 3G!

So a Grade B on ssllabs.com . A little work needed I think.

sslgrabeB

Qualys.com is a great resource for scanning URL’s to see what SSL/TLS cipher suites are in use. Check it out!

Disabling SSL v2, v3 and also RC4 in Apache2.

By the time I had finished typing this post I was up to a A- having disabled RC4 in the SSL.conf file in mods-enabled folder be appending the ‘SSLCipherSuite’ with :!RC4. Disabling SSL v2 and v3 is also a simple step by appending the ‘SSLProtocol’ line with ‘-SSLv3 -SSLv2’ in the same file.

This is very much only a small step towards securing a site, although a good start!

sslA

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Greetings!

Greetings! Welcome to my InfoSec Site!

Here I will be mostly be talking to myself about Information Security Topics, News, and mini guides. Feel free to join in and comment!

I am also going to be sharing some of the latest Labs and Projects that I am currently working on, short tutorials that I have been through and had to learn along the way. This will be both Windows and Linux based. I will also be sharing some Security techniques, not only in an effort to raise awareness for Information Security, but also to use as my own quick lookup when I need to remember something!

I was inspired to create this site after listening to Defensive Security Podcast and subsequently reading an article titled How to build a successful information security career on their site.

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