Delphi使用CRC加密算法對文件加密的例子。CRC就是簡單的用一個固定的數K去XOR待檢的串A，得出的余數R附加在這個A上給傳輸出去。在接收端，用同樣的這個數再去XOR。由於A XOR K=R，而B=A+R，如果傳輸過程沒有錯出錯,則B XOR K=(A+R)XOR K=R XOR k=0，校驗成功。（XOR是按位運算的）。CRC定義：在遠距離數據通信中，為確保高效而無差錯地傳送數據，必須對數據進行校驗，即差錯控制。循環冗余校驗CRC是對一個傳送數據塊進行校驗，是一種高效的差錯控制方法。
Delphi CRC文件加密，例子代碼：
01
unit Unit1;
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interface
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uses
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Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
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Dialogs, StdCtrls, Buttons;
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type
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TForm1 = class(TForm)
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Button1: TButton;
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Edit1: TEdit;
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SpeedButton1: TSpeedButton;
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OpenDialog1: TOpenDialog;
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procedure Button1Click(Sender: TObject);
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procedure SpeedButton1Click(Sender: TObject);
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private
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procedure CalcCRC32(FileName: String; var CRC32: dWord);
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{ Private declarations }
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public
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{ Public declarations }
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end;
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var
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Form1: TForm1;
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Fname : String;
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implementation
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{$R *.dfm}
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const Table: Array[0..255] of DWord =
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($00000000,$77073096,$EE0E612C,$990951BA,$076DC419,$706AF48F,$E963A535,$9E6495A3,$0EDB8832,$79DCB8A4,$E0D5E91E,$97D2D988,
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$09B64C2B,$7EB17CBD,$E7B82D07,$90BF1D91,$1DB71064,$6AB020F2,$F3B97148,$84BE41DE,$1ADAD47D,$6DDDE4EB,$F4D4B551,$83D385C7,
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$136C9856,$646BA8C0,$FD62F97A,$8A65C9EC,$14015C4F,$63066CD9,$FA0F3D63,$8D080DF5,$3B6E20C8,$4C69105E,$D56041E4,$A2677172,
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$3C03E4D1,$4B04D447,$D20D85FD,$A50AB56B,$35B5A8FA,$42B2986C,$DBBBC9D6,$ACBCF940,$32D86CE3,$45DF5C75,$DCD60DCF,$ABD13D59,
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$26D930AC,$51DE003A,$C8D75180,$BFD06116,$21B4F4B5,$56B3C423,$CFBA9599,$B8BDA50F,$2802B89E,$5F058808,$C60CD9B2,$B10BE924,
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$2F6F7C87,$58684C11,$C1611DAB,$B6662D3D,$76DC4190,$01DB7106,$98D220BC,$EFD5102A,$71B18589,$06B6B51F,$9FBFE4A5,$E8B8D433,
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$7807C9A2,$0F00F934,$9609A88E,$E10E9818,$7F6A0DBB,$086D3D2D,$91646C97,$E6635C01,$6B6B51F4,$1C6C6162,$856530D8,$F262004E,
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$6C0695ED,$1B01A57B,$8208F4C1,$F50FC457,$65B0D9C6,$12B7E950,$8BBEB8EA,$FCB9887C,$62DD1DDF,$15DA2D49,$8CD37CF3,$FBD44C65,
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$4DB26158,$3AB551CE,$A3BC0074,$D4BB30E2,$4ADFA541,$3DD895D7,$A4D1C46D,$D3D6F4FB,$4369E96A,$346ED9FC,$AD678846,$DA60B8D0,
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$44042D73,$33031DE5,$AA0A4C5F,$DD0D7CC9,$5005713C,$270241AA,$BE0B1010,$C90C2086,$5768B525,$206F85B3,$B966D409,$CE61E49F,
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$5EDEF90E,$29D9C998,$B0D09822,$C7D7A8B4,$59B33D17,$2EB40D81,$B7BD5C3B,$C0BA6CAD,$EDB88320,$9ABFB3B6,$03B6E20C,$74B1D29A,
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$EAD54739,$9DD277AF,$04DB2615,$73DC1683,$E3630B12,$94643B84,$0D6D6A3E,$7A6A5AA8,$E40ECF0B,$9309FF9D,$0A00AE27,$7D079EB1,
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$F00F9344,$8708A3D2,$1E01F268,$6906C2FE,$F762575D,$806567CB,$196C3671,$6E6B06E7,$FED41B76,$89D32BE0,$10DA7A5A,$67DD4ACC,
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$F9B9DF6F,$8EBEEFF9,$17B7BE43,$60B08ED5,$D6D6A3E8,$A1D1937E,$38D8C2C4,$4FDFF252,$D1BB67F1,$A6BC5767,$3FB506DD,$48B2364B,
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$D80D2BDA,$AF0A1B4C,$36034AF6,$41047A60,$DF60EFC3,$A867DF55,$316E8EEF,$4669BE79,$CB61B38C,$BC66831A,$256FD2A0,$5268E236,
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$CC0C7795,$BB0B4703,$220216B9,$5505262F,$C5BA3BBE,$B2BD0B28,$2BB45A92,$5CB36A04,$C2D7FFA7,$B5D0CF31,$2CD99E8B,$5BDEAE1D,
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$9B64C2B0,$EC63F226,$756AA39C,$026D930A,$9C0906A9,$EB0E363F,$72076785,$05005713,$95BF4A82,$E2B87A14,$7BB12BAE,$0CB61B38,
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$92D28E9B,$E5D5BE0D,$7CDCEFB7,$0BDBDF21,$86D3D2D4,$F1D4E242,$68DDB3F8,$1FDA836E,$81BE16CD,$F6B9265B,$6FB077E1,$18B74777,
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$88085AE6,$FF0F6A70,$66063BCA,$11010B5C,$8F659EFF,$F862AE69,$616BFFD3,$166CCF45,$A00AE278,$D70DD2EE,$4E048354,$3903B3C2,
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$A7672661,$D06016F7,$4969474D,$3E6E77DB,$AED16A4A,$D9D65ADC,$40DF0B66,$37D83BF0,$A9BCAE53,$DEBB9EC5,$47B2CF7F,$30B5FFE9,
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$BDBDF21C,$CABAC28A,$53B39330,$24B4A3A6,$BAD03605,$CDD70693,$54DE5729,$23D967BF,$B3667A2E,$C4614AB8,$5D681B02,$2A6F2B94,
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$B40BBE37,$C30C8EA1,$5A05DF1B,$2D02EF8D);
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procedure TForm1.Button1Click(Sender: TObject);
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var
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crc :dWord;
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begin
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if Fname<>'' then
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begin
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CalcCRC32(Fname,crc);
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if crc<>0 then
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ShowMessage(IntToHex(crc,6));
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end
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else
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showmessage('請選擇指定文件的路徑。');
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end;
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procedure TForm1.CalcCRC32(FileName: String; var CRC32: dWord);
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var F: file;
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BytesRead: dWord;
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Buffer: Array[1..65521] of byte;
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i: Word;
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begin
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FileMode := 0;
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CRC32 := $ffffffff;
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{$I-}
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AssignFile(F,FileName);
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Reset(F,1);
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if IOResult = 0 then
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begin
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repeat
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BlockRead(F,Buffer,SizeOf(Buffer),BytesRead);
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for i := 1 to BytesRead do
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CRC32 := (CRC32 shr 8) xor Table[Buffer[i] xor (CRC32 and $000000FF)];
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until BytesRead = 0;
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end;
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CloseFile(F);
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{$I+}
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CRC32 := not CRC32;
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end;
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procedure TForm1.SpeedButton1Click(Sender: TObject);
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begin
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if OpenDialog1.Execute then
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begin
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Edit1.Text := OpenDialog1.FileName;
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Fname := Trim(Edit1.Text);
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end
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else
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begin
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Edit1.Text := '';
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Fname := '';
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end;
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end;
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end.
可視化運行效果：
