In this article I am going to cover how the code is structured. To demonstrate the code structure I will use the Architectural Dependency diagrams in Visual Studio 2012.
The main solution file is split into 3 projects. There is the SafePadClientLibrary which contains the code for encrypting the documents, compression, and the handling of the SafePad file format. The domain objects in this library contain all the important routines for making the project work.
Recently I have been doing a bit of travelling for work to visit vendors and this has involved some lengthy train journeys. On these journeys I decided to set about writing a small little application that I had a use for. Initially I wanted a password vault, but when I thought about it more, I realised I wanted a secure way to store all sorts of information, like passwords, license keys, financial data etc.
So, whilst whiling away the hours on the train I started developing Safe Pad. The application is a pretty typical Rich Text based editor, but when you save your documents they are compressed and then stored by encrypting it with AES 256 three times using 2 passwords. This is a similar theory as to when the DES algorithms life was extended by using it to triple encrypt.
AES 256 is already a very strong algorithm, but when used in an application like this people still tend to use rather weak passwords which makes them susceptible to dictionary attacks. Because this application triple encrypts you are prompted to enter 2 passwords, therefore the program encrypts with password 1, then password 2, and then password 1 again. It adds that extra layer of protection for your secrets. Of course, this isn’t an excuse to use weak passwords, I still recommend using strong passwords made up of mixed case letters, numbers and non alpha-numeric symbols.
I have developed the program enough to a stable 1.0 release. It is quite basic, but then again it doesn’t need to be complicated. I have released the source code on CodePlex under the GNU Public license and this marks my first foray into the world of open source software development. Feel free to download the application if you think it will be useful to you. It costs nothing. If you are not interested in messing around with the source code, then there is an installer you can use to install the application. If you feel like adding some features, then the source code is available for you to play around with.
I was writing some code the other night on a little pet project I am working on and I needed to persist some data to disc. The data was quite large so I needed to compress it first. I have not used any of the compression libraries in .NET before so I had a little investigation and wrote the static methods below.
They are very easy to use, just pass in a byte array to compress and recieve a compressed byte array back out, and visa versa to decompress the data.
I thought I would share these code snippets as they are quite useful. Enjoy.
private static byte Compress(byte input)
using (var outputStream = new MemoryStream())
using (var zip = new GZipStream(outputStream, CompressionMode.Compress))
zip.Write(input, 0, input.Length);
compressesData = outputStream.ToArray();
private static byte Decompress(byte input)
using (var outputStream = new MemoryStream())
using (var inputStream = new MemoryStream(input))
using (var zip = new GZipStream(inputStream, CompressionMode.Decompress))
decompressedData = outputStream.ToArray();
This is the 2nd part in a small series on using encryption primitives in .NET. In the first article I concentrated on symmetric cryptography and more specifically the AES algorithm. In this article I will take a brief look at Asymmetric cryptography using the RSA system.
RSA is an algorithm for public-key cryptography that is based on the presumed difficulty of factoring large integers, the factoring problem. RSA stands for Ron Rivest, Adi Shamir and Leonard Adleman, who first publicly described the algorithm in 1977. Clifford Cocks, an English mathematician, had developed an equivalent system in 1973, but it was classified until 1997.
A user of RSA creates and then publishes the product of two large prime numbers, along with an auxiliary value, as their public key. The prime factors must be kept secret. Anyone can use the public key to encrypt a message, but with currently published methods, if the public key is large enough, only someone with knowledge of the prime factors can feasibly decode the message. Whether breaking RSA encryption is as hard as factoring is an open question known as the RSA problem.
The AES symmetric process is classed as an algorithm where the plain text goes through multiple computation rounds to produce the cipher text. RSA is different in that is it a mathematical process. I won’t go into too much detail of how the keys are generated, but as stated above it is all around the complexity of factoring large prime numbers. The actual encryption process is based around modular arithmetic. For more detailed information on how this works check out this very useful Wikipedia page.
Recently a few of the developers on my team decided to put a build monitor up on the TV we have in our team area. They settled on a system called Siren of Shame. Essentially this monitor tells you the health of your builds (we use it with TFS but it supports many more source code repositories and build systems). Siren of shame has a little twist though that has some other advantages.
The system is built around a leader board and points system. For a successful build you get 1 point. For a failed build you lose 4 points. Not only do you lose points, the PC that the monitor is running on emits a very loud trumpet like alarm, alerting the team to you failed build. It is really rather amusing when the alarm goes off, although not so amusing for the poor person who has broken his build!!!
You can also earn awards the longer you use the system like CI NINJA and other such funny power ups. You also get awarded points for fixing someone else’s broken build. Whilst this is all amusing and a bit of fun, it does encourage a slight behaviour change in a team. For a start, no one wants to be at the bottom of the leader board, so to get a better position in the board you need to check in little and often, no more only checking in once a day as this should be frowned upon anyway.
I think using this tool has made a difference to the team in the short time we have been using it. I would summarise the benefits as:
Visibility your build health.
Encourage developers to check in little and often.
Rewarded for fixing other peoples builds.
Promotes a little healthy competition.
More accuracy. No one wants that build siren going off as we poke fun at them..
In unit testing, all mocks are evil! Now there’s a controversial statement to start a blog post with, but let me explain. I am writing this from my own experience as a software developer and a leader of software developers. This is the sort of thing that software religious wars are made of, so if you agree, or disagree, I would love for you to share your thoughts in the comments.
I think Mocking libraries, although very powerful, can enable developers to over complicate their unit tests. Unit tests should be short and easy to understand. I have lost count of the times where I have seen a developer mock out more than they need to because of excessive class coupling in their code. Just because you can mock out any object doesn’t mean that you should and avoid reducing excessive coupling.
Cryptography is a subject that I personally find fascinating. It really is one of the mathematical branches of computer science that really does seem to have a sense of magic to it. But this “magic” normally comes at a price, and that is the need for some really heavy duty mathematics. This normally puts people off, including myself as I am no math genius.
Lots of cryptography books are very heavy on the math and theoretical aspects of encryption, like Applied Cryptography by Bruce Schneier, which is great if you want to delve that deep, but most people including software developers just need to understand at a higher level how the algorithms work and how best to apply them in real life. That is where this book, Everyday Cryptography: Fundamental Principles and Applications by Keith M. Martin, comes in. The book is structured as follows :