Author: Jonas Bilinkevicius
How to encrypt and decrypt files or strings
Answer:
Here's a simple yet effective encryption function:
1 unit EZCrypt;
2
3 {modeled by Ben Hochstrasser(bhoc@surfeu.ch) after some code snippet from Borland}
4
5 interface
6
7 uses
8 Windows, Classes;
9
10 type
11 TWordTriple = array[0..2] of Word;
12
13 function FileEncrypt(InFile, OutFile: string; Key: TWordTriple): boolean;
14 function FileDecrypt(InFile, OutFile: string; Key: TWordTriple): boolean;
15 function TextEncrypt(const s: string; Key: TWordTriple): string;
16 function TextDecrypt(const s: string; Key: TWordTriple): string;
17 function MemoryEncrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer;
18 TargetSize: Cardinal; Key: TWordTriple): boolean;
19 function MemoryDecrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer;
20 TargetSize: Cardinal; Key: TWordTriple): boolean;
21
22 implementation
23
24 function MemoryEncrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer;
25 TargetSize: Cardinal; Key: TWordTriple): boolean;
26 var
27 pIn, pOut: ^byte;
28 i: Cardinal;
29 begin
30 if SrcSize = TargetSize then
31 begin
32 pIn := Src;
33 pOut := Target;
34 for i := 1 to SrcSize do
35 begin
36 pOut^ := pIn^ xor (Key[2] shr 8);
37 Key[2] := Byte(pIn^ + Key[2]) * Key[0] + Key[1];
38 inc(pIn);
39 inc(pOut);
40 end;
41 Result := True;
42 end
43 else
44 Result := False;
45 end;
46
47 function MemoryDecrypt(Src: Pointer; SrcSize: Cardinal; Target: Pointer;
48 TargetSize: Cardinal; Key: TWordTriple): boolean;
49 var
50 pIn, pOut: ^byte;
51 i: Cardinal;
52 begin
53 if SrcSize = TargetSize then
54 begin
55 pIn := Src;
56 pOut := Target;
57 for i := 1 to SrcSize do
58 begin
59 pOut^ := pIn^ xor (Key[2] shr 8);
60 Key[2] := byte(pOut^ + Key[2]) * Key[0] + Key[1];
61 inc(pIn);
62 inc(pOut);
63 end;
64 Result := True;
65 end
66 else
67 Result := False;
68 end;
69
70 function TextCrypt(const s: string; Key: TWordTriple; Encrypt: Boolean): string;
71 var
72 bOK: Boolean;
73 begin
74 SetLength(Result, Length(s));
75 if Encrypt then
76 bOK := MemoryEncrypt(PChar(s), Length(s), PChar(Result), Length(Result), Key)
77 else
78 bOK := MemoryDecrypt(PChar(s), Length(s), PChar(Result), Length(Result), Key);
79 if not bOK then
80 Result := '';
81 end;
82
83 function FileCrypt(InFile, OutFile: string; Key: TWordTriple; Encrypt: Boolean):
84 boolean;
85 var
86 MIn, MOut: TMemoryStream;
87 begin
88 MIn := TMemoryStream.Create;
89 MOut := TMemoryStream.Create;
90 try
91 MIn.LoadFromFile(InFile);
92 MOut.SetSize(MIn.Size);
93 if Encrypt then
94 Result := MemoryEncrypt(MIn.Memory, MIn.Size, MOut.Memory, MOut.Size, Key)
95 else
96 Result := MemoryDecrypt(MIn.Memory, MIn.Size, MOut.Memory, MOut.Size, Key);
97 MOut.SaveToFile(OutFile);
98 finally
99 MOut.Free;
100 MIn.Free;
101 end;
102 end;
103
104 function TextEncrypt(const s: string; Key: TWordTriple): string;
105 begin
106 Result := TextCrypt(s, Key, True);
107 end;
108
109 function TextDecrypt(const s: string; Key: TWordTriple): string;
110 begin
111 Result := TextCrypt(s, Key, False);
112 end;
113
114 function FileEncrypt(InFile, OutFile: string; Key: TWordTriple): boolean;
115 begin
116 Result := FileCrypt(InFile, OutFile, Key, True);
117 end;
118
119 function FileDecrypt(InFile, OutFile: string; Key: TWordTriple): boolean;
120 begin
121 Result := FileCrypt(InFile, OutFile, Key, False);
122 end;
123
124 end.
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