An Analysis of MDX/MDD File Format

MDict is a multi-platform open dictionary

which are both questionable. It is not available for every platform, e.g. OS X, Linux. Its dictionary file format is not open. But this has not hindered its popularity, and many dictionaries have been created for it.

This is an attempt to reveal MDX/MDD file format, so that my favorite dictionaries, created by MDict users, could be used elsewhere.

MDict Files

MDict stores the dictionary definitions, i.e. (key word, explanation) in MDX file and the dictionary reference data, e.g. images, pronunciations, stylesheets in MDD file. Although holding different contents, these two file formats share the same structure.

MDict v1 and v2 Format

MdxBuilder 2.x creates v1 format and MdxBuilder 3.x creates v2 format.

MDict v3 Format

MdxBuilder 4.x creates v3 format. The major changes are,

• The file is divided into 4 blocks, i.e. key index, key data, record index and record data. And all blocks have the same structure. The decoded block holds type dependent data.

• Partial block data (first 16 bytes as now) is always encrypted (after possible compression), via _fast_encrypt or _salsa_encrypt. The encryption key derives globally from the dictionary header's UUID value (since MdxBuilder 4.0 RC4), :

  key = xxh64_digest(uuid[:18]) + xxh64_digest(uuid[18:])

  or individually from each block data's Adler-32 checksum (until MdxBuilder 4.0 RC2), :

  key = ripemd128(alder)

Example Programs

readmdict.py

readmdict.py is an example implementation in Python. This program can read/extract mdx/mdd files.

Note

python-lzo is required to read mdx files created with engine 1.2. xxhash is required to read mdx files created with engine 3.0. Get Windows version from http://www.lfd.uci.edu/~gohlke/pythonlibs

It can be used as a command line tool. Suppose one has oald8.mdx and oald8.mdd:

$ python readmdict.py -x oald8.mdx

This will create a dictionary file oald8.txt and a folder data for images, pronunciation audio files.

On Windows, one can also double click it and select the file in the popup dialog.

Or as a module:

In [1]: from readmdict import MDX, MDD

Read MDX file and print the first entry:

In [2]: mdx = MDX('oald8.mdx')

In [3]: items = mdx.items()

In [4]: next(items)
Out[4]:
('A',
 '<span style=\'display:block;color:black;\'>.........')

mdx is an object having all info from a MDX file. items is an iterator producing 2-item tuples. Of each tuple, the first element is the entry text and the second is the explanation. Both are UTF-8 encoded strings.

Read MDD file and print the first entry:

In [5]: mdd = MDD('oald8.mdd')

In [6]: items = mdd.items()

In [7]: next(items)
Out[7]: 
(u'\\pic\\accordion_concertina.jpg',
'\xff\xd8\xff\xe0\x00\x10JFIF...........')

mdd is an object having all info from a MDD file. items is an iterator producing 2-item tuples. Of each tuple, the first element is the file name and the second element is the corresponding file content. The file name is encoded in UTF-8. The file content is a plain bytes array.

Acknowledge

The file format gets fully disclosed by https://github.com/zhansliu/writemdict. The encryption part is taken into this project.