codegroup - Online in the Cloud

PROGRAM:

NAME

codegroup - encode / decode binary file as five letter codegroups

SYNOPSIS

codegroup -d|-e [ -u ] [ infile [ outfile ] ]

DESCRIPTION

For decades, spies have written their encoded messages in groups of five letters.

codegroup encodes any binary file into this form, allowing it to be transmitted through
any medium, and decodes files containing codegroups into the original input. Encoded
files contain a 16-bit cyclical redundancy check (CRC) and file size to verify, when
decoded, that the message is complete and correct. Files being decoded may contain other
information before and after the codegroups, allowing in-the-clear annotations to be
included.

codegroup makes no attempt, on its own, to prevent your message from being read.
Cryptographic security should be delegated to a package intended for that purpose, such as
pgp. codegroup can then be applied to the encrypted binary output, transforming it into
easily transmitted text. Text created by codegroup uses only upper case ASCII letters and
spaces. Unlike files encoded with uuencode or pgp's ``ASCII armour'' facility, the output
of codegroup can be easily (albeit tediously) read over the telephone, broadcast on
shortwave radio to agents in the field, or sent by telegram, telex, or Morse code.

To illustrate the difference, here are the first few lines of a binary file encoded by:

base64:
H4sICFJ9MzYAA2EudGFyAOxba3faSNKer+lf0SezO3YmgLnY2I6TyQIGgwOGBTtOYjuJEMJo
DJJGF1+ys//9rarulpqLHRi/mdk9G84JIKGuqq579eNkNn745q9sNru9tcXhs5gtFPAzm83l
xad88WyxmNssbhe3sps8m8ttZ/M/8K1vL9oPP0RBaPggypU1vrad+59zosj0HqAj9xF//pe8
WsaVNbTH1rfkAfoobm7ea//cZn4rtv/mNtq/kM9t/cCz31Io9foftz9nnW77oMdfcdMdWJe+

uuencode:
begin 644 data.bin
M'XL("&7._R\ VUO;V\ /9U+FN2XSF3G6H5OA1(?HOB<=/<7__X7TN<PJ[L&
M=?-&1;I+) B8 0;P?_Z'?WY_-=7Q"T_JSZ_6)X9?&"$\OU9[N'\A[A%^L^6=
M?^M[OOV+:9=UM9J^] MAS_ ;X0O]U];(Z?<WWE9_\^[/]ZMM\OO[CG'^2M\M
M_G(+,US/LWKZE1#C^YO?D_;O#G[7][2R^+0>XJ^&PI/\[?7-7U]KU=]SSWQ?

pgp:
-----BEGIN PGP MESSAGE-----
Version: 2.6.2i

hIwCCb8iTku3pBUBA/9oSDlfk/On9bwjmTnB98Eejr6agkPSi3n6hd8JkAtJd33f
kzFq18Jo0xzRUWZ7Di6Jq/FXpeI1yztVDqispbcYOP0aDv4JZOSF1kRsmJ9xK9Bo
Cv4a967IXPkkRsjIAkx0B39dYxCzf8kHUn4THmyV/b2qLUZ0cc+mr8hxFfFpuYSM

codegroup:
ZZZZZ YBPIL AIAIG FMOPP CPAAA DGNGP GPGPA ADNJN ELJKO ELIMO
GEOHF KIFGP IFBCB PKCPI YJMHE PHBHP PPOBH NCOHD AKLLL AGHFP
DEGEF LKELC EAIJI ABAGP AHPPO IHHPH OHPDF YNFPB ALEPO KMPKP
NGCHI GFPBI CBDML PFGHL LIHPC BOOBB HOLDO FJNHP OLHLL OPNIL

Only codegroup conforms to the telegraphic convention of all upper case letters, and
passes the ``telephone test'' of being readable without any modifiers such as ``capital''
and ``lower-case''. Avoiding punctuation marks and lower case letters makes the output of
codegroup much easier to transmit over a voice or traditional telegraphic link.

OPTIONS

-decode Decodes the input, previously created by codegroup, to recover the original
input file, and verifies it to detect truncation or corruption of the
contents.

-encode Encodes the input into an output text file containing five letter code groups
(default).

-usage Print how-to-call information.

All options may be abbreviated to a single letter.

APPLICATION NOTES

Encoding a binary file as ASCII characters inevitably increases its size. When used in
conjunction with existing compression and encryption tools, the resulting growth in file
size is usually acceptable. For example, a random extract of electronic mail 32768 bytes
in length was chosen as a test sample. Compression with gzip compacted the file to 15062
bytes. It was then encrypted for transmission to a single recipient with pgp, which
resulted in a 15233 byte file. (Even though pgp has its own compression, smaller files
usually result from initial compression with gzip. In this case, pgp alone would have
produced a file of 15420 bytes.)

codegroup transforms the encrypted file into a 37296 byte text file. Thus, due to
compression, the code groups for the encrypted file are only a little larger than the
original cleartext.

Restricting the character set and including spaces between groups results in substantially
larger output files than those produced by uuencode and pgp. Files encoded with codegroup
are about 2.5 times the size of the input file, while uuencode and pgp expand the file
only about 35%. codegroup is thus preferable only for applications where its limited
character set is an advantage.

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