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      property Initialized: boolean;
      property Id: integer;
      property Algorithm: string;
      property MaxKeySize: integer;
  
      class function SelfTest: boolean;
  
      procedure Init(const Key; Size: longword; InitVector: pointer); 
      procedure InitStr(const Key: string; HashType: TDCP_hashclass);
      procedure Burn; 
      procedure Reset;
      procedure Encrypt(const Indata; var Outdata; Size: longword); 
      procedure Decrypt(const Indata; var Outdata; Size: longword); 
      function EncryptStream(InStream, OutStream: TStream; Size: longword): longword;
      function DecryptStream(InStream, OutStream: TStream; Size: longword): longword;
      function EncryptString(const Str: string): string; 
      function DecryptString(const Str: string): string;					

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property Initialized: boolean;					

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property Id: integer;					

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property Algorithm: string;					

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property MaxKeySize: integer;					

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class function SelfTest: boolean;					

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procedure Init(const Key; Size: longword; InitVector: pointer);					

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  procedure TForm1.Button1Click(Sender: TObject);
  var
    Cipher: TDCP_rc4;
    Hash: TDCP_sha1;
    Digest: array[0..19] of byte;  // SHA-1 produces a 160bit (20byte) output
  begin
    Hash:= TDCP_sha1.Create(Self);
    Hash.Init;                     // initialize the hash
    Hash.UpdateStr(Edit1.Text);    // generate a hash of Edit1.Text
    Hash.Final(Digest);            // save the hash in Digest
    Hash.Free;
    Cipher:= TDCP_rc4.Create(Self);
    Cipher.Init(Digest,Sizeof(Digest)*8,nil);  // remember size is in BITS (hence sizeof*8)
    ...
    
procedure InitStr(const Key: string; HashType: TDCP_hashclass);					

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  procedure TForm1.Button1Click(Sender: TObject);
  var
    Cipher: TDCP_rc4;
  begin
    Cipher:= TDCP_rc4.Create(Self);
    Cipher.InitStr(InputBox('Passphrase','Enter a passphrase',''),TDCP_sha1); // prompt for a passphrase
    ...
    
procedure Burn;					

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procedure Reset;					

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  function TestCipher: boolean;
  const
    InData: array[0..9] of byte= ($01,$23,$45,$56,$67,$78,$89,$10,$AB,$FF);
  var
    Cipher: TDCP_rc4;
    Data: array[0..9] of byte;
  begin
    Cipher:= TDCP_rc4.Create(nil);
    Cipher.InitStr('Hello World',TDCP_sha1);   // initialize the cipher
    Cipher.Encrypt(InData,Data,Sizeof(Data));  // encrypt some known data
    Cipher.Decrypt(Data,Data,Sizeof(Data));    // now decrypt it
    Cipher.Burn;                               // clear keying information
    Cipher.Free;
    Result:= CompareMem(@InData,@Data,Sizeof(Data));  // compare input and output
  end;					

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  function TestCipher: boolean;
  const
    InData: array[0..9] of byte= ($01,$23,$45,$56,$67,$78,$89,$10,$AB,$FF);
  var
    Cipher: TDCP_rc4;
    Data: array[0..9] of byte;
  begin
    Cipher:= TDCP_rc4.Create(nil);
    Cipher.InitStr('Hello World',TDCP_sha1);   // initialize the cipher
    Cipher.Encrypt(InData,Data,Sizeof(Data));  // encrypt some known data
    Cipher.Reset;                              // reset chaining information
    Cipher.Decrypt(Data,Data,Sizeof(Data));    // now decrypt it
    Cipher.Burn;                               // clear keying information
    Cipher.Free;
    Result:= CompareMem(@InData,@Data,Sizeof(Data));  // compare input and output
  end;					

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procedure Encrypt(const Indata; var Outdata; Size: longword);					

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procedure Decrypt(const Indata; var Outdata; Size: longword);					

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function EncryptStream(InStream, OutStream: TStream; Size: longword): longword;					

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function DecryptStream(InStream, OutStream: TStream; Size: longword): longword;					

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function EncryptString(const Str: string): string;					

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function DecryptString(const Str: string): string;					

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  procedure TForm1.btnEncryptClick(Sender: TObject);
  var
    i: integer;
    Cipher: TDCP_rc4;
    KeyStr: string;
  begin
    KeyStr:= '';
    if InputQuery('Passphrase','Enter passphrase',KeyStr) then  // get the passphrase
    begin
      Cipher:= TDCP_rc4.Create(Self);
      Cipher.InitStr(KeyStr,TDCP_sha1);         // initialize the cipher with a hash of the passphrase
      for i:= 0 to Memo1.Lines.Count-1 do       // encrypt the contents of the memo
        Memo1.Lines[i]:= Cipher.EncryptString(Memo1.Lines[i]);
      Cipher.Burn;
      Cipher.Free;
    end;
  end;
  
  procedure TForm1.btnDecryptClick(Sender: TObject);
  var
    i: integer;
    Cipher: TDCP_rc4;
    KeyStr: string;
  begin
    KeyStr:= '';
    if InputQuery('Passphrase','Enter passphrase',KeyStr) then  // get the passphrase
    begin
      Cipher:= TDCP_rc4.Create(Self);
      Cipher.InitStr(KeyStr,TDCP_sha1);         // initialize the cipher with a hash of the passphrase
      for i:= 0 to Memo1.Lines.Count-1 do       // decrypt the contents of the memo
        Memo1.Lines[i]:= Cipher.DecryptString(Memo1.Lines[i]);
      Cipher.Burn;
      Cipher.Free;
    end;
  end;					

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  procedure TForm1.btnEncryptClick(Sender: TObject);
  var
    Cipher: TDCP_rc4;
    KeyStr: string;
    Source, Dest: TFileStream;
  begin
    KeyStr:= '';
    if InputQuery('Passphrase','Enter passphrase',KeyStr) then  // get the passphrase
    begin
      try
        Source:= TFileStream.Create(boxInputFile.Text,fmOpenRead);
        Dest:= TFileStream.Create(boxOutputFile.Text,fmCreate);
        Cipher:= TDCP_rc4.Create(Self);
        Cipher.InitStr(KeyStr,TDCP_sha1);              // initialize the cipher with a hash of the passphrase
        Cipher.EncryptStream(Source,Dest,Source.Size); // encrypt the contents of the file
        Cipher.Burn;
        Cipher.Free;
        Dest.Free;
        Source.Free;
        MessageDlg('File encrypted',mtInformation,[mbOK],0);
      except
        MessageDlg('File IO error',mtError,[mbOK],0);
      end;
    end;
  end;
  
  procedure TForm1.btnDecryptClick(Sender: TObject);
  var
    Cipher: TDCP_rc4;
    KeyStr: string;
    Source, Dest: TFileStream;
  begin
    KeyStr:= '';
    if InputQuery('Passphrase','Enter passphrase',KeyStr) then  // get the passphrase
    begin
      try
        Source:= TFileStream.Create(boxInputFile.Text,fmOpenRead);
        Dest:= TFileStream.Create(boxOutputFile.Text,fmCreate);
        Cipher:= TDCP_rc4.Create(Self);
        Cipher.InitStr(KeyStr,TDCP_sha1);              // initialize the cipher with a hash of the passphrase
        Cipher.DecryptStream(Source,Dest,Source.Size); // decrypt the contents of the file
        Cipher.Burn;
        Cipher.Free;
        Dest.Free;
        Source.Free;
        MessageDlg('File decrypted',mtInformation,[mbOK],0);
      except
        MessageDlg('File IO error',mtError,[mbOK],0);
      end;
    end;
  end;					

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  type
    TSomePacket= record
      Date: double;
      ToUserID: integer;
      FromUserID: integer;
      MsgLen: integer;
      Msg: string;
    end;
    
  procedure EncryptPacket(Cipher: TDCP_cipher; var Packet: TSomePacket);
  // encrypt the information packet with the cipher
  // if the cipher isn't initialized then prompt for passphrase
  begin
    if Cipher= nil then
      raise Exception.Create('Cipher hasn''t been created!')
    else
    begin
      if not Cipher.Initialized then        // check the cipher has been initialized
        Cipher.InitStr(InputBox('Passphrase','Enter passphrase',''),TDCP_sha1);
      if Cipher is TDCP_blockcipher then    // if a block cipher use CFB 8bit as encrypting small packets
        TDCP_blockcipher(Cipher).CipherMode:= cmCFB8bit; 
      // encrypt the record part by part, could do this in one go if it was a packed record
      Cipher.Encrypt(Packet.Date,Packet.Date,Sizeof(Packet.Date));  
      Cipher.Encrypt(Packet.ToUserID,Packet.ToUserID,Sizeof(Packet.ToUserID));
      Cipher.Encrypt(Packet.FromUserID,Packet.FromUserID,Sizeof(Packet.FromUserID));
      Cipher.Encrypt(Packet.MsgLen,Packet.MsgLen,Sizeof(Packet.MsgLen));
      Cipher.Encrypt(Packet.Msg[1],Packet.Msg[1],Length(Packet.Msg));  // slightly different for strings
      // don't bother resetting the cipher, instead keep the chaining information
    end;  
  end;