A simple example encryption system with a challenge!
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README.md

Mystikó

The word mystikó is from the Greek language and means secret. Keeping secrets safe from unauthorized eyes is the very core purpose of encryption.

This gem is only intended for educational purposes and should not be used in serious data security applications.

Any use for unlawful purposes is strictly forbidden.

Installation

Add this line to your application's Gemfile:

gem 'mystiko'

And then execute:

$ bundle

Or install it yourself as:

$ gem install mystiko

The mystiko gem itself is found at: ( https://rubygems.org/gems/mystiko )

Usage

Mystikó is both a ruby gem and a command line utility. In order to work with the encryption engine two things must be done:

  • An instance must be created. This is easily done with the new method.

and then one of the following two options:

  • Encryption is done with the encrypt method and appropriate parameters.
  • Decryption is done with the decrypt method and appropriate parameters.

The parameters take the form of classical named/hashed parameters. Supported parameters include:

  • in_str: "value" -- a string of input data.
  • in_file: "name" -- the name of a file of input data. Overrides in_str.
  • key: "value" -- the key to use for processing
  • generator: object -- a seeded, pseudo-random number generator. Overrides key.
  • out_str: "value" -- the string output is appended to this string.
  • out_file: "name" -- the name of a file of output data. Overrides out_str.
  • window: value -- the size, in bytes, of the shuffling window.

The methods encrypt and decrypt both also return the resultant string of data.

The command line utility displays the following message if started with no arguments or the "--help", "-h", or "-?" options.

Mystiko version 0.1.0

Usage summary:

$ mystiko <options>

--help,    -h, -?            # Display this help message.
--encrypt, -e                # Data is to be encrypted.
--decrypt, -d                # Data is to be decrypted.
--input,   -i <input data>   # Specify the input data string.
--read,    -r <file name>    # Specify the input data file name.
--write,   -w <file name>    # Specify the input data file name.
--key,     -k <key data>     # Specify the key data string.

Notes:
 - A command option and a key are always required.
 - Data input defaults to STDIN.
 - Data output defaults to STDOUT.
 - If -r is specified, -i is ignored.
 - String data may be optionally enclosed in " ... "

Principles of Operation

The Vernam Cypher

The mystikó gem is a modified Vernam cypher. The Vernam cypher works by taking a stream of input symbols and mapping them to output symbols. This mapping obscures the original data. The classic approach to this type of cypher is to have a random string of data of the same length as the plain text data. The two streams of data are combined using the XOR operation. To recover the original data, the cypher data is again combined with the random data with the XOR operation. After one use, the random data is never reused.

This works because the XOR operator exhibits the following identity:

(A ^ B ^ B) == A

This is the result of the fact that:

(X ^ X) == 0

and

(X ^ 0) == X

Excepting "end run" code cracking (getting the data before/after encryption or getting a copy of the random data) or incompetence (poor quality or reusing the random data) this code can be shown to be unbreakable.

It is also very cumbersome to use. It requires that both parties have access to large amounts of high quality random data that can only be used once. It requires that random data to be kept secret and that these random data remain synchronized.

The Pseudo-Random Shortcut

Given that large quantities of random data are bothersome to deal with, it was only natural that someone would start taking short-cuts. In this case, the one-time use random data was replaced by a pseudo-random data generator (PRNG). This transforms the Vernam cypher from unbreakable to laughably weak. Why?

  • Any PRNG used in this way, requires an initial seed value. This seed value is effectively the key of the cypher. To crack the code, the attacker only needs to compute the seed value.
  • Many messages start with a known sequence of bytes. A header if you will. These known bytes make it possible know what values were generated during the encryption process. This in turn allows the internal state of the PRNG to be modeled, greatly reducing the number of seed values that must be tested.
  • Once a sequence of random values is known, it is often easy to determine what values will follow. At this point, the code is broken.

The problem with the Vernam cypher is that it only maps input symbols to output symbols. The order of the symbols is not changed. With one-use truly random data, this is not a problem. Knowledge of a few random values tells us nothing about the values to follow. With a PRNG, they tell us a very great deal.

The Scrambled Vernam Cypher

To avoid the problems of the classical Vernam cypher, mystikó makes one significant change: The Scrambled Vernam Cypher first performs a PRNG controlled shuffle on the symbols followed by a mapping of input symbols to output symbols.

To recover data, the Scrambled Vernam Cypher decryption routine performs an anti-mapping of the symbols back to their original values followed by a controlled anti-shuffle of the data back to its original order.

This data shuffling denies any would-be attacker knowledge of the order of the input data. Thus even with standard message headers, the content of the original message is (hopefully) no longer relevant.

It remains to be seen if this is indeed the case. Comments, ideas, observations, and thoughts are welcomed. See below for contributing.

References

Contributing

Creating any encryption system is quite an undertaking. For this reason, any input is most welcomed. There are two basic plans by which this can be accomplished.

Plan A

  1. Fork it ( https://github.com/PeterCamilleri/mystiko/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

Plan B

Go to the GitHub repository and raise an issue calling attention to some aspect that could use some TLC or a suggestion or an idea.