Monthly Archives: October 2012

VIM – The CompSci Classic

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Learning to escape VIM

I have a confession, the first I launched vim I could not even work out how to quit it so I took the lazy way out and just closed the terminal. This put me right off vim for quite a while. Now its time to really try to learn it.

Vim has two modes: insert and normal, when you launch vim it will go straight into normal mode, from normal mode type i to switch to insert mode and then press ESC to return back to normal mode.

GOLDEN SECRET 1: To exit VIM, enter :q in the normal mode

Normal mode basics 
You can delete the character under the cursor using x and using :w to save. To cut the current line use dd, this will delete the text on the current line and also delete the line itself, the cursor will move to the next line, which is now where the original line was. To copy the current line use yy. Now to paste the recently cut line, use p  to insert the text onto the line below where the cursor currently is or P to insert text before cursor.

Instead of the arrow keys, you can make use of hjkl to move the cursor, but personal I prefer to use the arrow keys

Entering Insert mode
So far we have entered insert mode using i, there are some alternative ways to enter insert mode, which allow you to move to insert mode and perform a useful operation in one key stoke, some of the alternative methods to enter insert mode are:

  • a – insert mode and move cursor back one charactor
  • o – insert mode and insert a new line after the current one
  • O – insert mode and insert a new line before the current one
  • cw – insert mode and delete the current word
GOLDEN SECRET 2: Insert mode has auto complete, use Ctrl-n to activate

Moving around normal mode
As well as using the arrow keys (or hjkl) to navigate around normal mode, there are plenty of useful extra shortcuts for navigating around. 0 jumps to first character in the row and $ goes to the last character in the row. ^ jumps to the first non-blank character of a line and g_  goes to the last non_blank character of line.

To search for a particular work or character, use / and enter search term. This will move the cursor to the next occurrence of the search term after the cursor, so to search for the first occurrence of a term in a file, put the cursor at the start of the file and then use / to search for the term.

To jump to the start of the next word use w and to go to end of this word use e, when  a word is composed of letters and underscores only, if you want to word to include special characters use W and E instead

GOLDEN SECRET 3: % means go to corresponding (, { and [

Text editor basics
u is used to undo and Crtl-r to redo. To open a file use :e , :w to save, :saveas , 😡 to save and quit. :q! to quit without saving. . will repeat last   command and N will repeat the command N number of times. NG goes to line N and G is go to last line

 
 
GOLDEN SECRET 4: * means to next occurrence of word under cursor and # means go to previous

Fault Tolerance comes to Twitter in the form of Twimight

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Making twitter fault tolerance may not seem like a priority at first thought, I mean surely in the unlikely event of the network failure, those 17 year of girls can will just have to learn to wait before they can tweet about there new jimmy shoes.

But if you consider further the situations in which network failure is likely to occur such as natural disaster, this is when twitter is needed the most. Here is an xkcd to illustrate the point

Seismic WavesIts difficult, particularly if you didn’t grow up with twitter to understand why keeping social network alive in the event of a disaster is so important. But like it or not, twitter is just as essential in some peoples live than other (more traditional) communications form such as text messaging or TV broadcasts. In fact, it could be argued that since scarcity of information is often a problem for individuals in a disaster, the broadcast properties of twitter, make it potential more useful than  uni cast text messaging or voice calls.

TWIMIGHT

The application to which has introduced this ‘disaster mode’ to twitter is called Twimight, its a open source twitter application with a couple of very interesting features. I’ve going to test out the application on my nexus 7.

The basic interface of the application is very similar to that of the standard twitter application but an exploration of the overflow icon highlights a range of features, that could be particularly useful in a disaster.

The basic idea of how this application aims to enable connectivity in a disaster situation is as follows:

  • Android device users install the application and get there friends to do the same
  • Bluetooth is used to pair your android device with your friends android devices
  • Disaster occurs so network connection is lost and the user enables the ‘Disaster Mode’ within the application which turns on bluetooth in an always discoverable mode
  • The user tweets despite the lack of a network connection
  • The tweet is send (via bluetooth) to friends within range
  • The disaster is over and the network connection is restored
  • Tweets are automatically posted to the web

ANDROID SENSOR TWITTETH

Twimight also support a plug-in called android-sensor-twitteth

TDS COMMUNICATIONS

The twitter disaster server is used to collect user activity and environment data

THE PLATFORM

In case of a disaster, individuals do not want let any other peice of hardware to carry around but given that 3/4 of the world’s population now have access to a mobile phone and that twitter now has 500 million users, mobile twitter access has the potential to be a powerful force for good.

The UX is designed such that its simple to use in a stressful situation, with the user enabling the ‘disaster mode’ in the application with a simple check box (though this box is a little harder to find than I would ideally like)

USE OF BLUETOOTH

Before Bluetooth can be used for the automatic spreading of tweeter messages, the devices must be paired, those potential irritating to the user, this is essential to allow the application to make up of the bluetooth protocol.

Once the user has enabled ‘Disaster Mode’ the application enables bluetooth, scanning takes place every  2 mins +- 20 sec

IMPACT ON BATTERY LIFE

Power consumption is important considation for all mobile applications, in this case it is particularly important as its more unlikely that users will have access to pwer supplies and suitable chargers. In ‘disaster mode’ the use of bluetooth much therefore be considered carefully. Bluetooth scanning time need be as high as possible to increase the speed of the transition of tweet, whilst using minimal battery life. The power saving heretics for Twimight are set so that the scanning interval is  reduced when battery is less than 50 % and scanning is stopped when battery is less than 30 %.

CRITICAL MASS

This application like many others, we be almost unless to individuals unless the number of devices that the application is install on reaches a critical number such that in the case of a disaster, there is at least one individuals within bluetooth transmitting distance with the application installed

This application will not be able to reach this critical mass, because individuals will not have the foresight to install such an application, “just in case” they were to need the disaster mode it provides.

Consider instead, the hypothetical case that twitter was to adopt such a “disaster mode” into its own supported mobile application.

The official twitter application has 578,194 downloads from the play store and 500 million activated android devices. So twitter and android are powerful platforms but with a typical bluetooth range of 10 m and the requirement for pair devices, is bluetooth really the best wireless protocol for this use

CASE STUDY : TWITTER & GREAT EAST JAPAN EARTHQUAKE

Tsukuba is a city of 200,000 located in Ibaraki Prefecture, Japan. Tsukuda lost electricity, communication networks and water immediately after the Great East Japan Earthquake of March 2011. The lack of power meant that smart phones became key devices for communication. Muneo Kaigo has written an excellent Keio Communication Review, examining the use of twitter in Tsukuda in the 7 days following the earthquake and I thoroughly recommend it

SOURCES

twimight hosting on google code –  code.google.com/p/twimight/
twimight unofficial application location –  twimight.googlecode.com/files/twimight_0.9.2.apk
android-sernsor-twitteth hosting on google code – code.google.com/p/android-sensor-twitteth/
the paper – people.ee.ethz.ch/~hossmath/papers/extremecom11_twimight.pdf
presentation from Extremecom 2011 – www.slideshare.net/thossmann/twitter-in-disaster-mode-extremecom-2011 
Keio Communication Review No. 34, 2012 – Social Media Usage During Disasters
and Social Capital: Twitter and the Great East Japan Earthquake –

Heidi-ann

October 11, 2012

I’m off to Aberdeen to demo Signposts at the All Hands Digital Economy Conference, this is my first conference and I’m very existed 😀 😀

DNSSEC – A basic Intro

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This article aims to not just explain how DNSSEC work but why the protocols are designed the way that they are. I will begin with a simple mental model of public-key cryptography, then I highlight issues with scheme described so far and add complexity to fix issues as I highlight them. I finish the article with a simplified model of DNSSEC and a range of problems/question that I hope to explore in the next article.

DNSSEC is a collection of IETF specifications for securing DNS data. It is a set of extensions to DNS which provide to DNS resolvers with:

  • origin authentication of DNS data
  • authenticated denial of existence
  • data integrity

It does not provide the DNS resolvers with:

  • availability
  • confidentiality, DNSSEC results are not encrypted
  • protection from user mistakes/assumptions

DNSSEC aims to adds security to DNS, while maintaining backwards compatibility.

RFC 3833

DNSSEC protects DNS resolvers from forged DNS data, by digitally signing all DNSSEC replies. The DNS resolver is then able to check if the information it receives is identical to that information on the authoritative DNS server.

DNSSEC can also protect information such as cryptographic certificates stored in CERT records in DNS.

RFC 4398

RFC 4367

Negative article on DNSSEC

DNSSEC-bis is the name of the DNSSEC specification and the related RFCs are
4033 introduction & requirements, 4034 resource records for DNSSEC and 4035 on protocol modifications.

Public-key cryptography is the use of two keys, one public and one private to encrypt and decrypt a message. A message before encryption is referred to as plain text and a message after encryption is referred to as cipher text.

Public-key cryptography can be used to provide confidentiality or authentication.

To provide confidentiality, the public key is used for encryption so anyone can write a message but only the intended recipient has the private key which is used for decryption, so the only person who can decrypt the message is intended recipient.

To provide origin authentication, the private key is used for encryption so the only person who can send an encrypted message is the intended source. Then the public key is used for decryption so anyone can read the message, provided it was written by the intended source.

Figure 1 – How public key cryptography can be used to provide authentication or confidentiality

DNSSEC works by digitally signing the results of DNS look-ups using public-key cryptography. It uses public-key cryptography to provide authentication not confidentiality. This means that private key is used for encryption and the public key is used for decryption. So when a DNS resolver makes a DNSSEC query, then the response will be signed by the correct information source and then the DNS resolver will use the public key to decrypt the response, knowing the response is reliable as it was definitely send by the intended source.

So that’s the problem solved, the DNS responses will be encrypted by correct source and then all the DNS resolvers will decryption the responses using the public key. This ensures that the response was sent by the correct source so it provides source authentication as well an data integrity as it was signed using a private key.

Except that this model completely ignores the details of how DNS actually generates the replies to DNS query and what exactly is the “intended source” in this context.

So now I want to explain why the basic public-key cryptography scheme that I outline is not sufficient to provide authentication.

The cryptography scheme aimed to provide authentication between the DNS resolver and the source of the DNS response, but it didn’t consider the details of how this DNS response was generated.

The actually answer is that the “intended source” in DNS is an Authoritative Name Server, There are many authoritative name server forming a distributed database, each authoritative name server responses to a specific subset of the DNS queries.

The DNS resolver needs to locate the relevant authoritative name server, this is achieved through a chain of domain name servers, either recursively, iteratively or a hybrid of them both.

To generate the response to a DNS query for the DNS resolver, there are a series of request-replies. So for DNSSEC to meet its primary goal of providing authenticated responses, there needs to be authentication throughout the chain between the DNS resolver and the intended source, which is the authoritative name server.  When a DNSSEC enabled DNS resolver gets a response then it can use the public key to check that it was encrypted by the authoritative name server.

So now we have fixed the problem … Actually not

This solution would require that all DNS resolvers change because all DNS resolvers need to decrypt the DNSSEC response using the public key to get the the normal DNS response. Given that DNSSEC nees to be backwards compatible with DNS, this means we need to alter the above scheme.

So instead of encrypting and decrypting the whole DNS response, why don’t we add some text to the DNS response as another resource record and then encrypt and decrypt that text instead. This means that DNS resolvers that are not DNSSEC compatible can simply ignore the extra resource records. This extra bit of information therefore acts as a digital signature. This is actually used in DNSSEC and the new resource record is called RRSIG.

Now we have DNS record with an extra resource record called RRSIG, the authoritative name server has the private key and the DNS resolver use the public key to check that the DNS information received was from an authoritative name server. But where do the DNS resolvers get the public key from ?

A simple idea would be to have a single server with all public keys on, then all DNSSEC enabled resolvers could just request the public key from the central server. This is fundamentally flawed as its a centralized system which would completely defeat the purpose of DNS, which is to act as a distributed system.

Therefore we need a distributed system of our own to get the public keys to the DNSSEC enabled resolvers, why not use a system like DNS or even DNSSEC ?

DNSSEC gets the public key, from the authoritative name server to the DNSSEC enabled resolver by introducing another new resource record called DNSKEY. This has the public key in it so that the DNS resolver can use it to verify the RRSIG.

Done ? Nope of course not …

So its easy to assume that we finished here but as we developed the scheme we have actually introduced new issues, for example we have lost any data integrity. Its easy for a 3rd party to intersect a DNS query, change the data in the resources and set it forward to its destination. The DNSSEC enabled resolver would be nun the wiser, as the response to the DNSSEC query is still correctly signed and will have the correct RRSIG.

We can fix they by making the plain text in the RRSIG, a hash of the original message. This means that if the messaged is changed in transit then the DNS resolver will detect it because after decrypting the RRSIG text and hashing the other resource records, the results will no longer be the same because the hash generated from the DNSSEC response will be different to the RRSIG one as the text has been changed.

Lets review where we have got to so far…

DNSSEC uses public-key cryptography to provide authentication and data integrity between authoritative name servers and DNS resolvers. It does this using two new resource records, RRSIG and DNSKEY.

The authoritative name server hashes the RRs and then uses a private key to encode this hash, the result is placed in the RRSIG record and the public key is placed in the DNSKEY record. Then the DNS response moves though a chain of domain name servers to the DNS resolver. If the DNS resolver supports DNSSEC then it will use the public key in the DNSKEY record to decrypt the RRSIG, this will give a hash of the other RRs, the resolver can then hash the other RRs and compare the results.

So what is this public-key cryptography algorithm that DNSSEC uses and whats going to happen if its broken in the future ?

DNSSEC doesn’t use a specific algorithm. Both DNSKEY and RRSIG have a 8 bit number, which corresponds to the algorithm used, details of with values correspond to which algorithms is available here

This scheme has a big problem though…

Consider the following situation, I am an evil 3rd party would wants to return the incorrect DNS respond to a (DNSSEC enable) DNS resolver :

  1. The (DNSSEC enable) DNS resolver places a DNS request for www.google.com
  2. I spot this and I want to send a reply to this DNS request that will not be from the authoritative name server, managed by Google
  3. So I’m going to make my own response and make it appear as its has comes from the authoritative name server
  4. I create RR with the incorrect information and I then come up with my own public and private key pair, using the private key to encrypt the hash in the RRSIG and then place the public key in the DNSKEY record
  5. The DNS resolver then decrypts the RRSIG record using the key in the DNSKEY and checks that its a hash of the other RR records
  6. The DNS resolver believes that the response is from the authoritative name server at google

The problem is the above situation is that although the RRSIG and DNSKEY resource records aim to authenticate the other resource records, there is nothing to prevent a 3rd party changing the RRSIG and the DNSKEY. What we need is a method of authenticating the DNSKEY.

If we assume for a moment that the DNSKEY is authenticated, then a (DNSSEC enable) DNS resolver will be able to detect if the other resource records have been changed. As the decrypted RRSIG will not be a hash of the other resource records. If a evil 3rd party also when tries to also change the RRSIG value, so that the decrypted RRSIG is a hash of the changes made, then they can do this only if they know the private key. But they do not know the private key used and they cannot replace the public/private key pair as we have assumed that the DNSKEY is authenticated

So how can we ensure that the DNSKEY is from the authoritative name server ?

DNSSEC works around this is by signing the DNS replies at each step in the chain of response and reply. So when a domain name server queries another domain name server, not only is the expected result returned but also a flag indicating if that zone used DNSSEC and if it does it includes a hash of the DNSKEY record stored in a record called DS.

So far we have introduced 3 new resource records to DNS:

  • RRSIG – a hash of the other RRs that is encrypt using the private key by the authoritative name server
  • DNSKEY – the public key associated with the private key used to encrypt the RRSIG, a DNS resolver then using this public key to decypt the RRSIG and check that the plaintext is a hash of the other RRs
  • DS – a hash of the DNSKEY used in the zone that the DNS resolver is about to query so that the resolver can check that the response from the next name server query has not had the DNSKEY altered because it can check the DNSKEY received with DS received from the last name server.

This hash is then used when the name server queries the zone, as the DNSKEY returned hashed should match the DS RR from the previous query. If the response doesn’t include a DNSSEC RR or the DNSSEC hashed is not the same as the previously returned DS RR, then the integrity of the data has been comprised.
Example
This diagram attempt to demonstrate how the chain of DS and DNSKEY allows use to assume that the DNSKEY has not been tampered with. In this example, a DNS resolver queries the root DNS name server and its returned with the normal DNS response as well as a DS resource record. This DS RR is a hash of the DNSKEY that will be returned then the next DNS request is made. The DNS resolver then queries a TLD name server, this returns the normal DNS response as well as a DNSKEY and another DS. Now the DNS resolver can check that the response was from the TLD name server by checking that the DS that is recieved prevously from the root DNS name server is a hash of the DNSKEY. The DNS resolver can now contiune as it has the DS, which is a hash of the DNSKEY that should be returned by the next name server

Figure 2 – DNSSEC chain of trust created using corresponding DS and DNSKEY RRs, this assumes that the response from the root DNS can be trusted

 

How does the DNS resolver know that it can trust the result from the root DNS server ?

In the above example we cant guarantee that response from the root DNS server is actually from the root DNS server, this is why we introduce a trust anchor

Figure 3 – chain of trust between a trush anchor and the authoriatative name server using a series of DS and RRSIG resource records

But this appears just to move the problem, how can we trust the trust anchor ?
We get the DS resource record using a different method where we don’t need to authenticate the origin as we know that the message can’t have been intercepted (i.e. via the operating system)

As you can see we have created a chain of trust using a series of corresponding DS records and DNSKEYs, this means that when we reach the authoriative DNS name server, we know that we can trust the DNSKEY and that is will not have been tampered with.

There is a fun website here, which provides information on the chain of trust.

Thing to consider in the next article:

  • What’s the difference between a validating and non-validating stud resolver, which is better ?
  • DNSSEC also introduces NSEC and NSEC3 resource records, what are these used for ?
  • DNSSEC requires use of the “DO” flag in  EDNS, why don’t the DNS resolvers just ignore the RRSIG. DNSKEY and DS resource records ?
  • What happens if the authoriative name server do not support DNSSEC, how does the resolver know the difference between DNS response from an authoriative name server that don’t use DNSSEC and a attach where the evil 3rd party tries to pretent the the authoriative name server dose not use DNSSEC
  • How exactly goes the trust anchor get the DS for DNS root, what happens if the root DNS needs to update the DNSKEY and therefore the DS record in the trust anchor, if for example the cyptographic algorithm is broken
  • How does a authoriative name server prove that an DNS entery don’t exist ?
  • In July 2010, the DNSSEC was added to the root DNS, could you use DNSSEC before the root DNS support DNSEC if all other name server and the resolver supported DNSSEC ? DNS Lookaside validation ?
  • What happens when a name server between the root and authoriate name server doesnt support DNSSEC but the other name server involved do ?
  • Why are there additional timestamps in the RRSIG to limit the time that the signiture is valid ?
  • Why are these timestamps absolute not relative like TTLs ?
  • How are new keys implemented and what about the caching?
  • Whats zome emuation and how can it be dealt with ?