user
Implement a One-time pad, for encrypting and decrypting messages.  
To keep it simple, we will be using letters only.

Sub-Tasks

* **Generate** the data for a One-time pad (user needs to specify a filename and length)

:   The important part is to get "true random" numbers, e.g. from /dev/random

* **encryption / decryption** ( basically the same operation, much like Rot-13 )

:   For this step, much of Vigenère cipher could be reused,  
    with the key to be read from the file containing the One-time pad.

* optional: **management** of One-time pads: list, mark as used, delete, etc.

:   Somehow, the users needs to keep track which pad to use for which partner.

To support the management of pad-files:

* Such files have a file-extension ".1tp"
* Lines starting with "#" may contain arbitary meta-data (i.e. comments)
* Lines starting with "-" count as "used"
* Whitespace within the otp-data is ignored

For example, here is the data from Wikipedia:

```
# Example data - Wikipedia - 2014-11-13
-ZDXWWW EJKAWO FECIFE WSNZIP PXPKIY URMZHI JZTLBC YLGDYJ 
-HTSVTV RRYYEG EXNCGA GGQVRF FHZCIB EWLGGR BZXQDQ DGGIAK 
 YHJYEQ TDLCQT HZBSIZ IRZDYS RBYJFZ AIRCWI UCVXTW YKPQMK 
 CKHVEX VXYVCS WOGAAZ OUVVON GCNEVR LMBLYB SBDCDC PCGVJX 
 QXAUIP PXZQIJ JIUWYH COVWMJ UZOJHL DWHPER UBSRUJ HGAAPR 
 CRWVHI FRNTQW AJVWRT ACAKRD OZKIIB VIQGBK IJCWHF GTTSSE 
 EXFIPJ KICASQ IOUQTP ZSGXGH YTYCTI BAZSTN JKMFXI RERYWE 

```

See also

* one time pad encryption in Python
* snapfractalpop - One-Time-Pad Command-Line-Utility (C).
* Crypt-OTP-2.00 on CPAN (Perl)
assistant
(formerly Perl 6)

**Works with**: Rakudo version 2017.10

The task is somewhat under-specified, especially the third (optional) section so I'm skipping that for now. Each sub-task has it's own code.

**Sub-task one:** generate one-time-pad files.

This is a fairly basic otp file generator. Uses Crypt::Random for decently high quality random numbers. (Random bytes are drawn from /dev/urandom on Unix-like systems, and CryptGenRandom() on Windows.) It will ask for a file name to save to, and the number of lines you want. Each line can be used to encode up to 48 characters of data. Default is 1000 lines, Only generating 4 lines here for demonstration purposes. Saving the file to 'rosettacode.1tp'.

```
sub MAIN {
    put "Generate data for one time pad encryption.\n" ~
        "File will have .1tp extension.";
    my $fn;
    loop {
        $fn = prompt 'Filename for one time pad data: ';
        if $fn !~~ /'.1tp' $/ { $fn ~= '.1tp' }
        if $fn.IO.e {
            my $ow = prompt "$fn aready exists, over-write? y/[n] ";
            last if $ow ~~ m:i/'y'/;
            redo;
        }
        last;
    }

    put 'Each line will contain 48 characters of encyption data.';
    my $lines = prompt 'How many lines of data to generate? [1000] ';
    $lines ||= 1000;
    generate($fn, $lines);
    say "One-time-pad data saved to: ", $fn.IO.absolute;

    sub generate ( $fn, $lines) {
        use Crypt::Random;
        $fn.IO.spurt: "# one-time-pad encryption data\n" ~
          ((sprintf(" %s %s %s %s %s %s %s %s\n",
          ((('A'..'Z')[crypt_random_uniform(26)] xx 6).join) xx 8))
          xx $lines).join;
    }
}

```

Output:

```
Generate data for one time pad encryption.
File wile have .1tp extension.
Filename for one time pad data: rosettacode
Each line will contain 48 characters of encyption data.
How many lines of data to generate? [1000] 4
One-time-pad data saved to: /home/myhome/mydirectory/rosettacode.1tp

```

Sample file generated by above code:

```
# one-time-pad encryption data
 DSUJOU UUWDZD VHFWRR AJDMDC ERZDGD WWKLHJ YITCML FORXCV
 BXGFCL ANGCGY VTAEUG UYAIPK FXWMNI INDLOR JIDZQL BOFFQD
 JISNOS CMLRPW TFGELQ HPTMRN SHBBDP AIVDAC CEWIFH TRLQVK
 FRBUUC GDCQHQ CEEURS RGVWVT JZIQLP NQCABF BWUPUI UDTZAF
```

**Sub-task two:** encrypt/decrypt text using the otp files generated by part one.

One-time-pad encryption gets it's security from the fact that the pads are used **one time**. As a line is used in the otp file, it needs to be marked as used, or removed so it doesn't get reused. Theoretically, you would make a copy of rosettacode.1tp and send it by secure means to the receiver of your encrypted text so that they can use it to decrypt. Since we are encrypting and decrypting on the same computer, we'll make a copy of the otp file named rosettacopy.1tp and use that for decryption so the encrypt and decrypt functions don't conflict.

```
sub s2v ($s) { $s.uc.comb(/ <[ A..Z ]> /)».ord »-» 65 }
sub v2s (@v) { (@v »%» 26 »+» 65)».chr.join }

sub hide   ($secret, $otp) { v2s(s2v($secret) »+» s2v($otp)) }
sub reveal ($hidden, $otp) { v2s(s2v($hidden) »-» s2v($otp)) }

sub otp-data ($fn, $lines) {
    my $fh = $fn.IO.open :rw;
    my $data;
    my $count = 0;
    repeat {
        my $pos = $fh.tell;
        my $line = $fh.get;
        if $line.substr(0,1) ne '-'|'#' {
            $data ~= $line;
            $fh.seek($pos);
            $fh.put: '-' ~ $line.substr(1);
            $count++;
        }
    } until $count == $lines or $fh.eof;
    note "Insufficient lines of data remaining in $fn" if $count != $lines;
    $data;
}

sub otp-size (Str $string) { ceiling $string.uc.comb(/ <[ A..Z ]> /) / 48 }

sub otp-encrypt ( $secret, $fn ) {
    my $otp-size = otp-size $secret;
    my $otp-data = otp-data($fn, $otp-size);
    my $encrypted = hide $secret, $otp-data;
    # pad encryted text out to a full line with random text
    $encrypted ~= ('A'..'Z').roll while $encrypted.chars % 48;
    join "\n", $encrypted.comb(6).rotor(8, :partial).map:
      { sprintf "{ join ' ', "%s" xx $_ }", $_ };
}

sub otp-decrypt ( $secret, $fn ) {
    my $otp-size = otp-size $secret;
    my $otp-data = otp-data($fn, $otp-size);
    my $plain-text = reveal $secret, $otp-data;
    join "\n", $plain-text.comb(6).rotor(8, :partial).map:
      { sprintf "{ join ' ', "%s" xx $_ }", $_ };
}

my $otp-encrypt-fn = 'rosettacode.1tp';
my $otp-decrypt-fn = 'rosettacopy.1tp';

my $secret = "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!";

say "Secret:\n$secret\n\nEncrypted:";
say my $encrypted =   otp-encrypt $secret,    $otp-encrypt-fn;
say "\nDecrypted:\n", otp-decrypt $encrypted, $otp-decrypt-fn;

```

Output:

```
Secret:
Beware the Jabberwock, my son! The jaws that bite, the claws that catch!

Encrypted:
EWQJFY NBAMZE WLWSFT KVBERP XYDMGZ OPRLAK GBXVTP HZRTUO
IXZHCE CUUORL THOFDI DCXRLG JQICPI ZEREHP RLOEAE PRMVJH

Decrypted:
BEWARE THEJAB BERWOC KMYSON THEJAW STHATB ITETHE CLAWST
HATCAT CHOMLN YOOBJC JEXJWW ETMQCA RROTTY IDLFKT ODHQTE
```

Contents of rosettacode.1tp after encryption / rosettacopy.1tp after decryption:

```
# one-time-pad encryption data
-DSUJOU UUWDZD VHFWRR AJDMDC ERZDGD WWKLHJ YITCML FORXCV
-BXGFCL ANGCGY VTAEUG UYAIPK FXWMNI INDLOR JIDZQL BOFFQD
 JISNOS CMLRPW TFGELQ HPTMRN SHBBDP AIVDAC CEWIFH TRLQVK
 FRBUUC GDCQHQ CEEURS RGVWVT JZIQLP NQCABF BWUPUI UDTZAF
```