https://github.com/vesche/pmhsc

poor man's homophonic substitution cipher
https://github.com/vesche/pmhsc

cipher homophonic homophonic-substitution-ciphers homophony python substitution-cipher

Last synced: about 2 months ago
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poor man's homophonic substitution cipher

• Host: GitHub
• URL: https://github.com/vesche/pmhsc
• Owner: vesche
• License: unlicense
• Created: 2017-06-02T04:47:53.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2021-12-29T00:14:05.000Z (about 3 years ago)
• Last Synced: 2023-02-26T08:41:12.843Z (almost 2 years ago)
• Topics: cipher, homophonic, homophonic-substitution-ciphers, homophony, python, substitution-cipher
• Language: Python
• Homepage:
• Size: 13.7 KB
• Stars: 8
• Watchers: 2
• Forks: 5
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# pmhsc - Poor Man's Homophonic Substitution Cipher

This is a Python command-line tool for an implementation of a [homophonic substitution cipher](https://en.wikipedia.org/wiki/Substitution_cipher#Homophonic_substitution). Upon generating a `mapping.p` file, pmhsc takes 8 random, non-repeating letters and gathers all the permutations with repetitions (Cartesian product) of those letters (8^8 or 16,777,216 unique strings). These permutations are then shuffled, and dispersed equally 27 ways (26 letters of the alphabet and space). This gives each letter 621,378 unique representations (or mappings). When a message is encrypted one of these 621,378 strings belonging to each letter are selected at random to represent each character. During decryption strings are searched for and remapped to their original letters.

Seeing as we still cannot break some homophonic substitution ciphers from the eighteen hundreds that were comprised of 50,000 symbols or less, I'm fairly certain that this cipher can be used to very safely share relatively short, important, nerdy messages. Swap `mapping.p` files with your homies face-to-face, and then send each other all the secret messages. <3

A little while after making pmhsc I came back and created **Rich Man's Homophonic Substitution Cipher** which can encrypt any file type (not just ASCII) with a homophonic cipher similar to pmhsc. It's notably less strong, but this is mostly just for fun anyhow (read: just use OTP). It uses an 8-letter [isogram](https://en.wikipedia.org/wiki/Isogram) (`espinoza` in this case) and takes the Cartesian product of that string to produce 8^8 unique strings. It then takes every possible value of 8-bits (2^8 or 256 states) and disperses the 8^8 unique strings to these 256 states. This gives each 8-bit state 65,536 unique representations. Encryption and decryption occurs the same as pmhsc.

See below for the usage and results of both of these tools.

## Usage (pmhsc)

```

$ python pmhsc.py

usage: pmhsc.py [-h] [-g] [-e] [-d] [-m MAPPING] [-i INPUT] [-o OUTPUT]

poor mans homophonic substitution cipher

optional arguments:

  -h, --help            show this help message and exit

  -g, --genmaps         generate mapping file

  -e, --encrypt         encrypt a file

  -d, --decrypt         decrypt a file

  -m MAPPING, --mapping MAPPING

                        specify a mapping file to use (default: mapping.p)

  -i INPUT, --input INPUT

                        input file

  -o OUTPUT, --output OUTPUT

                        output file

$ python pmhsc.py --genmaps

Mapping completed in 85.75 seconds.

$ du -sh mapping.p

358M	mapping.p

$ python pmhsc.py --encrypt -i example/example.txt -o example/example.enc

Encryption completed in 41.94 seconds.

$ python pmhsc.py --decrypt -i example/example.enc -o example/example.dec

Decryption completed in 161.18 seconds.

```

# Usage (rmhsc)

```

$ python rmhsc.py --help

usage: rmhsc.py [-h] [-g] [-e] [-d] [-i INPUT] [-o OUTPUT]

rich man's homophonic substitution cipher

optional arguments:

  -h, --help            show this help message and exit

  -g, --genmaps         generate mapping file

  -e, --encrypt         encrypt a file

  -d, --decrypt         decrypt a file

  -i INPUT, --input INPUT

                        input file

  -o OUTPUT, --output OUTPUT

                        output file

$ python rmhsc.py -g

Generating mapping file...

Completed genmaps in 32.41 seconds.

$ du -sh mapping.p

289M	mapping.p

$ python rmhsc.py --encrypt -i example/1x1.png -o example/1x1.enc

Encrypting file...

Completed encryption in 1.90 seconds.

$ python rmhsc.py --decrypt -i example/1x1.enc -o example/1x1.dec

Decrypting file...

Completed decryption in 40.88 seconds.

$ md5sum example/1x1.*

71a50dbba44c78128b221b7df7bb51f1  example/1x1.dec

e26386ee59797c96ba40d38c91aab23f  example/1x1.enc

71a50dbba44c78128b221b7df7bb51f1  example/1x1.png

```

## Results

pmhsc:

```

$ cat example.txt

Perhaps it had something to do with living in a dark cupboard, but

Harry had always been small and skinny for his age. He looked even

smaller and skinnier than he really was because all he had to wear were

old clothes of Dudley's, and Dudley was about four times bigger than he

...

$ cat example.enc

b kbkk rrkdknrkvrqkbvd bdnkq nr nqrvbvrbbvkvknbqb nbd nvvd  dkrqvrvvqrddqrvrdd

rqnqnvvnbdk rbvvkdqdb bvvnrqbvr vkqrvrbvqvq dbndknqndq rrvdbrqdb vkrkkrvvqdvdkb

n bkqkrk kqkkq qvqqvbdd q rqd bdv vv r rqvvd qdndrd k vbnkdk vqkkqkvqndnnnbnbrkr

drbrkv kbbr dqndqnbnnqr kdqbvqqbvdkdnd dkdr  kkrnnkbqdnbv kkk qkbn  qddrdnbnqb

...

$ cat example.dec

perhaps it had something to do with living in a dark cupboard but

harry had always been small and skinny for his age he looked even

smaller and skinnier than he really was because all he had to wear were

old clothes of dudleys and dudley was about four times bigger than he

...

```

rmhsc:

```

$ xxd 1x1.png

00000000: 8950 4e47 0d0a 1a0a 0000 000d 4948 4452  .PNG........IHDR

00000010: 0000 0001 0000 0001 0103 0000 0025 db56  .............%.V

00000020: ca00 0000 0350 4c54 4500 0000 a77a 3dda  .....PLTE....z=.

00000030: 0000 0001 7452 4e53 0040 e6d8 6600 0000  [email protected]...

00000040: 0a49 4441 5408 d763 6000 0000 0200 01e2  .IDAT..c`.......

00000050: 21bc 3300 0000 0049 454e 44ae 4260 82    !.3....IEND.B`.

$ cat 1x1.enc

nposaznsonipzppeeoppzponpniiopiepizapniiaaznipppsosanpznnaninoiiioaoapinpazansa

ozszsaaieaiiossanionpaisnianaepioapsszzassapoopionieoazszaszszenizzsoaippsanoap

panipznooziepezzsnzononazosoonpezinaispiipznoipaapenoioapananpaoaaiipsniiasnnzo

noapnzaoezeaepeniaaipozzzeeeepasepsspaapspzeansoaepiaeoeiospponiioeaazpoazaipop

...

```