Dada uma mensagem de texto simples e uma chave numérica, cifra/decifra o texto fornecido usando o algoritmo Rail Fence. 
A cifra da cerca ferroviária (também chamada de cifra em zigue-zague) é uma forma de cifra de transposição. Seu nome deriva da maneira como é codificado. 
Exemplos:  

    Encryption     
 Input : 'GeeksforGeeks '   
 Key = 3   
 Output : GsGsekfrek eoe   
    Decryption     
 Input : GsGsekfrek eoe   
 Key = 3   
 Output : 'GeeksforGeeks '   
  
    Encryption     
 Input : 'defend the east wall'   
 Key = 3   
 Output : dnhaweedtees alf tl   
    Decryption     
 Input : dnhaweedtees alf tl   
 Key = 3   
 Output : defend the east wall   
  
    Encryption     
 Input : 'attack at once'   
 Key = 2    
 Output : atc toctaka ne    
    Decryption     
 Input : 'atc toctaka ne'   
 Key = 2   
 Output : attack at once   
 
    Criptografia    
  
 Em uma cifra de transposição, a ordem dos alfabetos é reorganizada para obter o texto cifrado.   
 

  
 
 Na cifra da cerca ferroviária, o texto simples é escrito para baixo e diagonalmente nos trilhos sucessivos de uma cerca imaginária.  
 
 Quando alcançamos o trilho inferior, percorremos para cima movendo-nos diagonalmente. Depois de chegar ao trilho superior, a direção muda novamente. Assim, os alfabetos da mensagem são escritos em zigue-zague.  
 
 Após cada alfabeto ter sido escrito, as linhas individuais são combinadas para obter o texto cifrado.  
 
 
  
 Por exemplo, se a mensagem for 'GeeksforGeeks' e o número de trilhos = 3, a cifra será preparada como:    
    
   .'.Sua criptografia será feita em linha, ou seja, GSGSEKFREKEOE 
  
    
  
    Descriptografia    
  
 Como vimos anteriormente, o número de colunas na cifra da barreira ferroviária permanece igual ao comprimento da mensagem de texto simples. E a chave corresponde ao número de trilhos.   
    
  
 
 Portanto, a matriz ferroviária pode ser construída de acordo. Uma vez obtida a matriz, podemos descobrir os locais onde os textos devem ser colocados (usando a mesma forma de mover-se diagonalmente para cima e para baixo alternativamente).  
 
 Em seguida, preenchemos a linha do texto cifrado. Após preenchê-lo percorremos a matriz em zigue-zague para obter o texto original.  
 
 
  
 Implementação:    
 Seja cipher-text = 'GsGsekfrek eoe' e Key = 3    
    
  
 
 Número de colunas na matriz = len(texto cifrado) = 13  
 
 Número de linhas = chave = 3  
 
 
  
 Portanto, a matriz original será 3*13, agora marcando lugares com texto como '*' obtemos    
    
  
 * _ _ _ * _ _ _ * _ _ _ *   
 _ * _ * _ * _ * _ * _ *    
 _ _ * _ _ _ * _ _ _ * _    
 
  
 Abaixo está um programa para criptografar/descriptografar a mensagem usando o algoritmo acima.    
    
 C++   
   // C++ program to illustrate Rail Fence Cipher   // Encryption and Decryption   #include          using     namespace     std  ;   // function to encrypt a message   string     encryptRailFence  (  string     text       int     key  )   {      // create the matrix to cipher plain text      // key = rows  length(text) = columns      char     rail  [  key  ][(  text  .  length  ())];      // filling the rail matrix to distinguish filled      // spaces from blank ones      for     (  int     i  =  0  ;     i      <     key  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     text  .  length  ();     j  ++  )      rail  [  i  ][  j  ]     =     'n'  ;      // to find the direction      bool     dir_down     =     false  ;      int     row     =     0       col     =     0  ;      for     (  int     i  =  0  ;     i      <     text  .  length  ();     i  ++  )      {      // check the direction of flow      // reverse the direction if we've just      // filled the top or bottom rail      if     (  row     ==     0     ||     row     ==     key  -1  )      dir_down     =     !  dir_down  ;      // fill the corresponding alphabet      rail  [  row  ][  col  ++  ]     =     text  [  i  ];      // find the next row using direction flag      dir_down  ?  row  ++     :     row  --  ;      }      //now we can construct the cipher using the rail matrix      string     result  ;      for     (  int     i  =  0  ;     i      <     key  ;     i  ++  )      for     (  int     j  =  0  ;     j      <     text  .  length  ();     j  ++  )      if     (  rail  [  i  ][  j  ]  !=  'n'  )      result  .  push_back  (  rail  [  i  ][  j  ]);      return     result  ;   }   // This function receives cipher-text and key   // and returns the original text after decryption   string     decryptRailFence  (  string     cipher       int     key  )   {      // create the matrix to cipher plain text      // key = rows  length(text) = columns      char     rail  [  key  ][  cipher  .  length  ()];      // filling the rail matrix to distinguish filled      // spaces from blank ones      for     (  int     i  =  0  ;     i      <     key  ;     i  ++  )      for     (  int     j  =  0  ;     j      <     cipher  .  length  ();     j  ++  )      rail  [  i  ][  j  ]     =     'n'  ;      // to find the direction      bool     dir_down  ;      int     row     =     0       col     =     0  ;      // mark the places with '*'      for     (  int     i  =  0  ;     i      <     cipher  .  length  ();     i  ++  )      {      // check the direction of flow      if     (  row     ==     0  )      dir_down     =     true  ;      if     (  row     ==     key  -1  )      dir_down     =     false  ;      // place the marker      rail  [  row  ][  col  ++  ]     =     '*'  ;      // find the next row using direction flag      dir_down  ?  row  ++     :     row  --  ;      }      // now we can construct the fill the rail matrix      int     index     =     0  ;      for     (  int     i  =  0  ;     i   <  key  ;     i  ++  )      for     (  int     j  =  0  ;     j   <  cipher  .  length  ();     j  ++  )      if     (  rail  [  i  ][  j  ]     ==     '*'     &&     index   <  cipher  .  length  ())      rail  [  i  ][  j  ]     =     cipher  [  index  ++  ];      // now read the matrix in zig-zag manner to construct      // the resultant text      string     result  ;      row     =     0       col     =     0  ;      for     (  int     i  =  0  ;     i   <     cipher  .  length  ();     i  ++  )      {      // check the direction of flow      if     (  row     ==     0  )      dir_down     =     true  ;      if     (  row     ==     key  -1  )      dir_down     =     false  ;      // place the marker      if     (  rail  [  row  ][  col  ]     !=     '*'  )      result  .  push_back  (  rail  [  row  ][  col  ++  ]);      // find the next row using direction flag      dir_down  ?  row  ++:     row  --  ;      }      return     result  ;   }   //driver program to check the above functions   int     main  ()   {      cout      < <     encryptRailFence  (  'attack at once'       2  )      < <     endl  ;      cout      < <     encryptRailFence  (  'GeeksforGeeks '       3  )      < <     endl  ;      cout      < <     encryptRailFence  (  'defend the east wall'       3  )      < <     endl  ;      //Now decryption of the same cipher-text      cout      < <     decryptRailFence  (  'GsGsekfrek eoe'    3  )      < <     endl  ;      cout      < <     decryptRailFence  (  'atc toctaka ne'    2  )      < <     endl  ;      cout      < <     decryptRailFence  (  'dnhaweedtees alf tl'    3  )      < <     endl  ;      return     0  ;   }   
  Java   
   // Java program to illustrate Rail Fence Cipher   // Encryption and Decryption   import     java.util.Arrays  ;   class   RailFence     {      // function to encrypt a message      public     static     String     encryptRailFence  (  String     text        int     key  )      {      // create the matrix to cipher plain text      // key = rows  length(text) = columns      char  [][]     rail     =     new     char  [  key  ][  text  .  length  ()  ]  ;      // filling the rail matrix to distinguish filled      // spaces from blank ones      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      Arrays  .  fill  (  rail  [  i  ]       'n'  );      boolean     dirDown     =     false  ;      int     row     =     0       col     =     0  ;      for     (  int     i     =     0  ;     i      <     text  .  length  ();     i  ++  )     {      // check the direction of flow      // reverse the direction if we've just      // filled the top or bottom rail      if     (  row     ==     0     ||     row     ==     key     -     1  )      dirDown     =     !  dirDown  ;      // fill the corresponding alphabet      rail  [  row  ][  col  ++]     =     text  .  charAt  (  i  );      // find the next row using direction flag      if     (  dirDown  )      row  ++  ;      else      row  --  ;      }      // now we can construct the cipher using the rail      // matrix      StringBuilder     result     =     new     StringBuilder  ();      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     text  .  length  ();     j  ++  )      if     (  rail  [  i  ][  j  ]     !=     'n'  )      result  .  append  (  rail  [  i  ][  j  ]  );      return     result  .  toString  ();      }      // This function receives cipher-text and key      // and returns the original text after decryption      public     static     String     decryptRailFence  (  String     cipher        int     key  )      {      // create the matrix to cipher plain text      // key = rows  length(text) = columns      char  [][]     rail     =     new     char  [  key  ][  cipher  .  length  ()  ]  ;      // filling the rail matrix to distinguish filled      // spaces from blank ones      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      Arrays  .  fill  (  rail  [  i  ]       'n'  );      // to find the direction      boolean     dirDown     =     true  ;      int     row     =     0       col     =     0  ;      // mark the places with '*'      for     (  int     i     =     0  ;     i      <     cipher  .  length  ();     i  ++  )     {      // check the direction of flow      if     (  row     ==     0  )      dirDown     =     true  ;      if     (  row     ==     key     -     1  )      dirDown     =     false  ;      // place the marker      rail  [  row  ][  col  ++]     =     '*'  ;      // find the next row using direction flag      if     (  dirDown  )      row  ++  ;      else      row  --  ;      }      // now we can construct the fill the rail matrix      int     index     =     0  ;      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     cipher  .  length  ();     j  ++  )      if     (  rail  [  i  ][  j  ]     ==     '*'      &&     index      <     cipher  .  length  ())      rail  [  i  ][  j  ]     =     cipher  .  charAt  (  index  ++  );      StringBuilder     result     =     new     StringBuilder  ();      row     =     0  ;      col     =     0  ;      for     (  int     i     =     0  ;     i      <     cipher  .  length  ();     i  ++  )     {      // check the direction of flow      if     (  row     ==     0  )      dirDown     =     true  ;      if     (  row     ==     key     -     1  )      dirDown     =     false  ;      // place the marker      if     (  rail  [  row  ][  col  ]     !=     '*'  )      result  .  append  (  rail  [  row  ][  col  ++]  );      // find the next row using direction flag      if     (  dirDown  )      row  ++  ;      else      row  --  ;      }      return     result  .  toString  ();      }      // driver program to check the above functions      public     static     void     main  (  String  []     args  )      {      // Encryption      System  .  out  .  println  (  'Encrypted Message: '  );      System  .  out  .  println  (      encryptRailFence  (  'attack at once'       2  ));      System  .  out  .  println  (      encryptRailFence  (  'GeeksforGeeks '       3  ));      System  .  out  .  println  (      encryptRailFence  (  'defend the east wall'       3  ));      // Now decryption of the same cipher-text      System  .  out  .  println  (  'nDecrypted Message: '  );      System  .  out  .  println  (      decryptRailFence  (  'atc toctaka ne'       2  ));      System  .  out  .  println  (      decryptRailFence  (  'GsGsekfrek eoe'       3  ));      System  .  out  .  println  (      decryptRailFence  (  'dnhaweedtees alf tl'       3  ));      }   }   // This code is contributed by Jay   
  Python3   
   # Python3 program to illustrate   # Rail Fence Cipher Encryption   # and Decryption   # function to encrypt a message   def   encryptRailFence  (  text     key  ):   # create the matrix to cipher   # plain text key = rows    # length(text) = columns   # filling the rail matrix   # to distinguish filled   # spaces from blank ones   rail   =   [[  '  n  '   for   i   in   range  (  len  (  text  ))]   for   j   in   range  (  key  )]   # to find the direction   dir_down   =   False   row     col   =   0     0   for   i   in   range  (  len  (  text  )):   # check the direction of flow   # reverse the direction if we've just   # filled the top or bottom rail   if   (  row   ==   0  )   or   (  row   ==   key   -   1  ):   dir_down   =   not   dir_down   # fill the corresponding alphabet   rail  [  row  ][  col  ]   =   text  [  i  ]   col   +=   1   # find the next row using   # direction flag   if   dir_down  :   row   +=   1   else  :   row   -=   1   # now we can construct the cipher   # using the rail matrix   result   =   []   for   i   in   range  (  key  ):   for   j   in   range  (  len  (  text  )):   if   rail  [  i  ][  j  ]   !=   '  n  '  :   result  .  append  (  rail  [  i  ][  j  ])   return  (  ''   .   join  (  result  ))   # This function receives cipher-text   # and key and returns the original   # text after decryption   def   decryptRailFence  (  cipher     key  ):   # create the matrix to cipher   # plain text key = rows    # length(text) = columns   # filling the rail matrix to   # distinguish filled spaces   # from blank ones   rail   =   [[  '  n  '   for   i   in   range  (  len  (  cipher  ))]   for   j   in   range  (  key  )]   # to find the direction   dir_down   =   None   row     col   =   0     0   # mark the places with '*'   for   i   in   range  (  len  (  cipher  )):   if   row   ==   0  :   dir_down   =   True   if   row   ==   key   -   1  :   dir_down   =   False   # place the marker   rail  [  row  ][  col  ]   =   '*'   col   +=   1   # find the next row   # using direction flag   if   dir_down  :   row   +=   1   else  :   row   -=   1   # now we can construct the   # fill the rail matrix   index   =   0   for   i   in   range  (  key  ):   for   j   in   range  (  len  (  cipher  )):   if   ((  rail  [  i  ][  j  ]   ==   '*'  )   and   (  index    <   len  (  cipher  ))):   rail  [  i  ][  j  ]   =   cipher  [  index  ]   index   +=   1   # now read the matrix in   # zig-zag manner to construct   # the resultant text   result   =   []   row     col   =   0     0   for   i   in   range  (  len  (  cipher  )):   # check the direction of flow   if   row   ==   0  :   dir_down   =   True   if   row   ==   key  -  1  :   dir_down   =   False   # place the marker   if   (  rail  [  row  ][  col  ]   !=   '*'  ):   result  .  append  (  rail  [  row  ][  col  ])   col   +=   1   # find the next row using   # direction flag   if   dir_down  :   row   +=   1   else  :   row   -=   1   return  (  ''  .  join  (  result  ))   # Driver code   if   __name__   ==   '__main__'  :   print  (  encryptRailFence  (  'attack at once'     2  ))   print  (  encryptRailFence  (  'GeeksforGeeks '     3  ))   print  (  encryptRailFence  (  'defend the east wall'     3  ))   # Now decryption of the   # same cipher-text   print  (  decryptRailFence  (  'GsGsekfrek eoe'     3  ))   print  (  decryptRailFence  (  'atc toctaka ne'     2  ))   print  (  decryptRailFence  (  'dnhaweedtees alf tl'     3  ))   # This code is contributed   # by Pratik Somwanshi   
  C#   
   using     System  ;   class     GFG_RailFence     {      // function to encrypt a message      public     static     string     EncryptRailFence  (  string     text       int     key  )     {      // create the matrix to cipher plain text      // key = rows length(text) = columns      char  []     rail     =     new     char  [  key       text  .  Length  ];      // filling the rail matrix to distinguish filled      // spaces from blank ones      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     text  .  Length  ;     j  ++  )      rail  [  i       j  ]     =     'n'  ;      bool     dirDown     =     false  ;      int     row     =     0       col     =     0  ;      for     (  int     i     =     0  ;     i      <     text  .  Length  ;     i  ++  )     {      // check the direction of flow      // reverse the direction if we've just      // filled the top or bottom rail      if     (  row     ==     0     ||     row     ==     key     -     1  )      dirDown     =     !  dirDown  ;      // fill the corresponding alphabet      rail  [  row       col  ++  ]     =     text  [  i  ];      // find the next row using direction flag      if     (  dirDown  )      row  ++  ;      else      row  --  ;      }      // now we can construct the cipher using the rail      // matrix      string     result     =     ''  ;      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     text  .  Length  ;     j  ++  )      if     (  rail  [  i       j  ]     !=     'n'  )      result     +=     rail  [  i       j  ];      return     result  ;      }      // This function receives cipher-text and key      // and returns the original text after decryption      public     static     string     DecryptRailFence  (  string     cipher       int     key  )     {      // create the matrix to cipher plain text      // key = rows length(text) = columns      // create the matrix to cipher plain text      // key = rows  length(text) = columns      char  []     rail     =     new     char  [  key       cipher  .  Length  ];      // filling the rail matrix to distinguish filled      // spaces from blank ones      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     cipher  .  Length  ;     j  ++  )      rail  [  i       j  ]     =     'n'  ;      // to find the direction      bool     dirDown     =     true  ;      int     row     =     0       col     =     0  ;      // mark the places with '*'      for     (  int     i     =     0  ;     i      <     cipher  .  Length  ;     i  ++  )     {      // check the direction of flow      if     (  row     ==     0  )      dirDown     =     true  ;      if     (  row     ==     key     -     1  )      dirDown     =     false  ;      // place the marker      rail  [  row       col  ++  ]     =     '*'  ;      // find the next row using direction flag      if     (  dirDown  )      row  ++  ;      else      row  --  ;      }      // now we can construct the fill the rail matrix      int     index     =     0  ;      for     (  int     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     cipher  .  Length  ;     j  ++  )      if     (  rail  [  i       j  ]     ==     '*'     &&     index      <     cipher  .  Length  )      rail  [  i       j  ]     =     cipher  [  index  ++  ];      // create the result string      string     result     =     ''  ;      row     =     0  ;      col     =     0  ;      // iterate through the rail matrix      for     (  int     i     =     0  ;     i      <     cipher  .  Length  ;     i  ++  )     {      // check the direction of flow      if     (  row     ==     0  )      dirDown     =     true  ;      if     (  row     ==     key     -     1  )      dirDown     =     false  ;      // place the marker      if     (  rail  [  row       col  ]     !=     '*'  )      result     +=     rail  [  row       col  ++  ];      // find the next row using direction flag      if     (  dirDown  )      row  ++  ;      else      row  --  ;      }      return     result  ;      }      // driver program to check the above functions      public     static     void     Main  ()     {      // Encryption      Console  .  WriteLine  (  'Encrypted Message: '  );      Console  .  WriteLine  (  EncryptRailFence  (  'attack at once'       2  ));      Console  .  WriteLine  (      EncryptRailFence  (  'GeeksforGeeks '       3  ));      Console  .  WriteLine  (      EncryptRailFence  (  'defend the east wall'       3  ));      // Now decryption of the same cipher-text      Console  .  WriteLine  (  'nDecrypted Message: '  );      Console  .  WriteLine  (      DecryptRailFence  (  'atc toctaka ne'       2  ));      Console  .  WriteLine  (      DecryptRailFence  (  'GsGsekfrek eoe'       3  ));      Console  .  WriteLine  (      DecryptRailFence  (  'dnhaweedtees alf tl'       3  ));      }   }   
  JavaScript   
   // function to encrypt a message   function     encryptRailFence  (  text       key  )     {      // create the matrix to cipher plain text      // key = rows  text.length = columns      let     rail     =     new     Array  (  key  ).  fill  ().  map  (()     =>     new     Array  (  text  .  length  ).  fill  (  'n'  ));      // filling the rail matrix to distinguish filled      // spaces from blank ones      let     dir_down     =     false  ;      let     row     =     0       col     =     0  ;      for     (  let     i     =     0  ;     i      <     text  .  length  ;     i  ++  )     {      // check the direction of flow      // reverse the direction if we've just      // filled the top or bottom rail      if     (  row     ==     0     ||     row     ==     key     -     1  )     dir_down     =     !  dir_down  ;      // fill the corresponding alphabet      rail  [  row  ][  col  ++  ]     =     text  [  i  ];      // find the next row using direction flag      dir_down     ?     row  ++     :     row  --  ;      }      // now we can construct the cipher using the rail matrix      let     result     =     ''  ;      for     (  let     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  let     j     =     0  ;     j      <     text  .  length  ;     j  ++  )      if     (  rail  [  i  ][  j  ]     !=     'n'  )     result     +=     rail  [  i  ][  j  ];      return     result  ;   }   // function to decrypt a message   function     decryptRailFence  (  cipher       key  )     {      // create the matrix to cipher plain text      // key = rows  text.length = columns      let     rail     =     new     Array  (  key  ).  fill  ().  map  (()     =>     new     Array  (  cipher  .  length  ).  fill  (  'n'  ));      // filling the rail matrix to mark the places with '*'      let     dir_down     =     false  ;      let     row     =     0       col     =     0  ;      for     (  let     i     =     0  ;     i      <     cipher  .  length  ;     i  ++  )     {      // check the direction of flow      if     (  row     ==     0  )     dir_down     =     true  ;      if     (  row     ==     key     -     1  )     dir_down     =     false  ;      // place the marker      rail  [  row  ][  col  ++  ]     =     '*'  ;      // find the next row using direction flag      dir_down     ?     row  ++     :     row  --  ;      }      // now we can construct the rail matrix by filling the marked places with cipher text      let     index     =     0  ;      for     (  let     i     =     0  ;     i      <     key  ;     i  ++  )      for     (  let     j     =     0  ;     j      <     cipher  .  length  ;     j  ++  )      if     (  rail  [  i  ][  j  ]     ==     '*'     &&     index      <     cipher  .  length  )     rail  [  i  ][  j  ]     =     cipher  [  index  ++  ];      // now read the matrix in zig-zag manner to construct the resultant text      let     result     =     ''  ;      row     =     0       col     =     0  ;      for     (  let     i     =     0  ;     i      <     cipher  .  length  ;     i  ++  )     {      // check the direction of flow      if     (  row     ==     0  )     dir_down     =     true  ;      if     (  row     ==     key     -     1  )     dir_down     =     false  ;      // place the marker      if     (  rail  [  row  ][  col  ]     !=     '*'  )     result     +=     rail  [  row  ][  col  ++  ];      // find the next row using direction flag      dir_down     ?     row  ++     :     row  --  ;      }      return     result  ;   }   // driver program to check the above functions      // Encryption   console  .  log  (  encryptRailFence  (  'attack at once'       2  ));      console  .  log  (  encryptRailFence  (  'GeeksforGeeks'       3  ));      console  .  log  (  encryptRailFence  (  'defend the east wall'       3  ));   // Now decryption of the same cipher-text   console  .  log  (  decryptRailFence  (  'GsGsekfrek eoe'       3  ));   console  .  log  (  decryptRailFence  (  'atc toctaka ne'       2  ));   console  .  log  (  decryptRailFence  (  'dnhaweedtees alf tl'       3  ));   
    
  Saída   
atc toctaka ne GsGsekfrek eoe dnhaweedtees alf tl GeeksforGeeks attack at once defend the east wall  
 
    Complexidade de tempo:    O(linha * coluna)   
    Espaço Auxiliar:    O(linha * coluna)    
    Referências:      
   https://en.wikipedia.org/wiki/Rail_fence_cipher     
 Este artigo é uma contribuição de       Ashutosh Kumar          
    
    
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