Rosetta Code

Playfair cipher

Revision as of 16:56, 21 May 2013 by rosettacode>Bearophile (Small improvements in Python entry)

Implement a Playfair cipher encryption and decryption.

Playfair cipher is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

The user must be able to choose J = I or no Q in the alphabet. The output of the encrypted and decrypted message must be in capitalized digraphs, separated by spaces.

Output example: HI DE TH EG OL DI NT HE TR EX ES TU MP.

C++

<lang cpp>#include <iostream>

  1. include <string>

using namespace std;

class playfair { public: 

   void doIt( string k, string t, bool ij, bool e )
   {

createGrid( k, ij ); getTextReady( t, ij, e ); if( e ) doIt( 1 ); else doIt( -1 ); display(); 

   }

private: 

   void doIt( int dir )
   {

int a, b, c, d; string ntxt; for( string::const_iterator ti = _txt.begin(); ti != _txt.end(); ti++ ) { if( getCharPos( *ti++, a, b ) ) if( getCharPos( *ti, c, d ) ) { if( a == c ) { ntxt += getChar( a, b + dir ); ntxt += getChar( c, d + dir ); } else if( b == d ){ ntxt += getChar( a + dir, b ); ntxt += getChar( c + dir, d ); } else { ntxt += getChar( c, b ); ntxt += getChar( a, d ); } } } _txt = ntxt; 

   }

   void display()
   {

cout << "\n\n OUTPUT:\n=========" << endl; string::iterator si = _txt.begin(); int cnt = 0; while( si != _txt.end() ) { cout << *si; si++; cout << *si << " "; si++; if( ++cnt >= 26 ) cout << endl, cnt = 0; } cout << endl << endl; 

   }

   char getChar( int a, int b )
   {

return _m[b % 5][a % 5]; 

   }

   bool getCharPos( char l, int &a, int &b )
   {

for( int y = 0; y < 5; y++ ) for( int x = 0; x < 5; x++ ) if( _m[y][x] == l ) { a = x; b = y; return true; }

return false; 

   }

   void getTextReady( string t, bool ij, bool e )
   {

for( string::iterator si = t.begin(); si != t.end(); si++ ) { *si = toupper( *si ); if( *si < 65 || *si > 90 ) continue; if( *si == 'J' && ij ) *si = 'I'; else if( *si == 'Q' && !ij ) continue; _txt += *si; } if( e ) { string ntxt = ""; size_t len = _txt.length(); for( size_t x = 0; x < len; x += 2 ) { ntxt += _txt[x]; if( x + 1 < len ) { if( _txt[x] == _txt[x + 1] ) ntxt += 'X'; ntxt += _txt[x + 1]; } } _txt = ntxt; } if( _txt.length() & 1 ) _txt += 'X'; 

   }

   void createGrid( string k, bool ij )
   {

if( k.length() < 1 ) k = "KEYWORD"; k += "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; string nk = ""; for( string::iterator si = k.begin(); si != k.end(); si++ ) { *si = toupper( *si ); if( *si < 65 || *si > 90 ) continue; if( ( *si == 'J' && ij ) || ( *si == 'Q' && !ij ) )continue; if( nk.find( *si ) == -1 ) nk += *si; } copy( nk.begin(), nk.end(), &_m[0][0] ); 

   }

   string _txt; char _m[5][5];

};

int main( int argc, char* argv[] ) { 

   string key, i, txt; bool ij, e;
   cout << "(E)ncode or (D)ecode? "; getline( cin, i ); e = ( i[0] == 'e' || i[0] == 'E' );
   cout << "Enter a en/decryption key: "; getline( cin, key ); 
   cout << "I <-> J (Y/N): "; getline( cin, i ); ij = ( i[0] == 'y' || i[0] == 'Y' );
   cout << "Enter the text: "; getline( cin, txt ); 
   playfair pf; pf.doIt( key, txt, ij, e ); return system( "pause" );

}</lang>

Output:


(E)ncode or (D)ecode? e
Enter a en/decryption key: playfair example
I <-> J (Y/N): y
Enter the text: Hide the gold in the tree stump

OUTPUT:
=========
BM OD ZB XD NA BE KU DM UI XM MO UV IF



(E)ncode or (D)ecode? d
Enter a en/decryption key: playfair example
I <-> J (Y/N): y
Enter the text: BMODZBXDNABEKUDMUIXMMOUVIF

OUTPUT:
=========
HI DE TH EG OL DI NT HE TR EX ES TU MP

Perl 6

<lang perl6># Instantiate a specific encoder/decoder.

sub playfair( $key, 

             $from = 'J',

$to = $from eq 'J' ?? 'I' !! ) { 

   sub canon($str) { $str.subst(/<-alpha>/,, :g).uc.subst(/$from/,$to,:g) }

   # Build 5x5 matrix.
   my @m = canon($key ~ ('A'..'Z').join).comb.uniq.map:

-> $a,$b,$c,$d,$e { [$a,$b,$c,$d,$e] } 

   # Pregenerate all forward translations.
   my %ENC = gather {

# Map pairs in same row. for @m -> @r { for ^@r X ^@r -> \i,\j { next if i == j; take @r[i] ~ @r[j] => @r[(i+1)%5] ~ @r[(j+1)%5]; } }

# Map pairs in same column. for ^5 -> $c { my @c = @m.map: *.[$c]; for ^@c X ^@c -> \i,\j { next if i == j; take @c[i] ~ @c[j] => @c[(i+1)%5] ~ @c[(j+1)%5]; } }

# Map pairs with cross-connections. for ^5 X ^5 X ^5 X ^5 -> \i1,\j1,\i2,\j2 { next if i1 == i2 or j1 == j2; take @m[i1][j1] ~ @m[i2][j2] => @m[i1][j2] ~ @m[i2][j1]; } 

   }

   # Generate reverse translations.
   my %DEC = %ENC.invert;

   return

anon sub enc($red) { my @list = canon($red).comb(/(.) (.?) <?{ $1 ne $0 }>/); ~@list.map: { .chars == 1 ?? %ENC{$_~'X'} !! %ENC{$_} } }, anon sub dec($black) { my @list = canon($black).comb(/../); ~@list.map: { %DEC{$_} } } }

my (&encode,&decode) = playfair 'Playfair example';

my $orig = "Hide the gold in...the TREESTUMP!!!"; say " orig:\t$orig";

my $black = encode $orig; say "black:\t$black";

my $red = decode $black; say " red:\t$red";</lang>

Output:
 orig:	Hide the gold in...the TREESTUMP!!!
black:	BM OD ZB XD NA BE KU DM UI XM MO UV IF
  red:	HI DE TH EG OL DI NT HE TR EX ES TU MP

Python

Translation of: Perl 6

<lang python>from string import uppercase from itertools import product from re import findall

def uniq(seq): 

   seen = {}
   return [seen.setdefault(x, x) for x in seq if x not in seen]

def partition(seq, n): 

   return [seq[i : i + n] for i in xrange(0, len(seq), n)]


"""Instantiate a specific encoder/decoder.""" def playfair(key, from_ = 'J', to = None): 

   if to is None:
       to = 'I' if from_ == 'J' else 

   def canonicalize(s):
       return filter(lambda c: c in uppercase, s.upper()).replace(from_, to)

   # Build 5x5 matrix.
   m = partition(uniq(canonicalize(key + uppercase)), 5)

   # Pregenerate all forward translations.
   enc = {}

   # Map pairs in same row.
   for row in m:
       for i, j in product(xrange(5), repeat=2):
           if i != j:
               enc[row[i] + row[j]] = row[(i + 1) % 5] + row[(j + 1) % 5]

   # Map pairs in same column.
   for c in zip(*m):
       for i, j in product(xrange(5), repeat=2):
           if i != j:
               enc[c[i] + c[j]] = c[(i + 1) % 5] + c[(j + 1) % 5]

   # Map pairs with cross-connections.
   for i1, j1, i2, j2 in product(xrange(5), repeat=4):
       if i1 != i2 and j1 != j2:
           enc[m[i1][j1] + m[i2][j2]] = m[i1][j2] + m[i2][j1]

   # Generate reverse translations.
   dec = dict((v, k) for k, v in enc.iteritems())

   def sub_enc(txt):
       lst = findall(r"(.)(?:(?!\1)(.))?", canonicalize(txt))
       return " ".join(enc[a + (b if b else 'X')] for a, b in lst)

   def sub_dec(encoded):
       return " ".join(dec[p] for p in partition(canonicalize(encoded), 2))

   return sub_enc, sub_dec


(encode, decode) = playfair("Playfair example") orig = "Hide the gold in...the TREESTUMP!!!" print "Original:", orig enc = encode(orig) print "Encoded:", enc print "Decoded:", decode(enc)</lang>

Output:
Original: Hide the gold in...the TREESTUMP!!!
Encoded: BM OD ZB XD NA BE KU DM UI XM MO UV IF
Decoded: HI DE TH EG OL DI NT HE TR EX ES TU MP
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