mnemonicode: A C repository from devshane

Oren Tirosh is no longer maintaining the original version of this project.
Stephen Paul Weber likes it and is making it accessible on GitHub.

These routines implement a method for encoding binary data into a sequence
of words which can be spoken over the phone, for example, and converted
back to data on the other side.

For more information see <http://web.archive.org/web/20101031205747/http://www.tothink.com/mnemonic/>

There are some other somewhat similar systems that seem less satisfactory:

- OTP was designed for easy typing, and for minimizing length, but as
a consequence the word list contains words that are similar ("AD"
and "ADD") that are poor for dictating over the phone

- PGPfone has optimized "maximum phonetic distance" between words,
which resolves the above problem but has some other drawbacks:

- Low efficiency, as it encodes a little less than 1 bit per
character;

- Word quality issues, as some words are somewhat obscure to
non-native speakers of English, or are awkward to use or type.

Mnemonic tries to do better by being more selective about its word
list. Its criteria are thus:

Mandatory Criteria:

- The wordlist contains 1626 words.

- All words are between 4 and 7 letters long.

- No word in the list is a prefix of another word (e.g. visit,
visitor).

- Five letter prefixes of words are sufficient to be unique.

Less Strict Criteria:

- The words should be usable by people all over the world. The list
is far from perfect in that respect. It is heavily biased towards
western culture and English in particular. The international
vocabulary is simply not big enough. One can argue that even words
like "hotel" or "radio" are not truly international. You will find
many English words in the list but I have tried to limit them to
words that are part of a beginner's vocabulary or words that have
close relatives in other european languages. In some cases a word
has a different meaning in another language or is pronounced very
differently but for the purpose of the encoding it is still ok - I
assume that when the encoding is used for spoken communication
both sides speak the same language.

- The words should have more than one syllable. This makes them
easier to recognize when spoken, especially over a phone
line. Again, you will find many exceptions. For one syllable words
I have tried to use words with 3 or more consonants or words with
diphthongs, making for a longer and more distinct
pronounciation. As a result of this requirement the average word
length has increased. I do not consider this to be a problem since
my goal in limiting the word length was not to reduce the average
length of encoded data but to limit the maximum length to fit in
fixed-size fields or a terminal line width.

- No two words on the list should sound too much alike. Soundalikes
such as "sweet" and "suite" are ruled out. One of the two is
chosen and the other should be accepted by the decoder's
soundalike matching code or using explicit aliases for some words.

- No offensive words. The rule was to avoid words that I would not
like to be printed on my business card. I have extended this to
words that by themselves are not offensive but are too likely to
create combinations that someone may find embarrassing or
offensive. This includes words dealing with religion such as
"church" or "jewish" and some words with negative meanings like
"problem" or "fiasco". I am sure that a creative mind (or a random
number generator) can find plenty of embarrasing or offensive word
combinations using only words in the list but I have tried to
avoid the more obvious ones. One of my tools for this was simply a
generator of random word combinations - the problematic ones stick
out like a sore thumb.

- Avoid words with tricky spelling or pronounciation. Even if the
receiver of the message can probably spell the word close enough
for the soundalike matcher to recognize it correctly I prefer
avoiding such words. I believe this will help users feel more
comfortable using the system, increase the level of confidence and
decrease the overall error rate. Most words in the list can be
spelled more or less correctly from hearing, even without knowing
the word.

- The word should feel right for the job. I know, this one is very
subjective but some words would meet all the criteria and still
not feel right for the purpose of mnemonic encoding. The word
should feel like one of the words in the radio phonetic alphabets
(alpha, bravo, charlie, delta etc).

mnemonic.h Header file
mnemonic.c Encoding/decoding and associated routines
mn_wordlist.c The word list itself
mnencode.c Sample program - encode data from stdin to stdout
mndecode.c Sample program - decode data from stdin to stdout

== Other Implementations ==

JavaScript: <https://github.com/mbrubeck/mnemonic.js>
Go: <https://bitbucket.org/dchapes/mnemonicode>

devshane/mnemonicode