rsa.pas

rsa加密算法实例

{License, info, etc
 ------------------

This implementation is made by Walied Othman, to contact me
mail to [e-mail] or
[e-mail], or ICQ me on 20388046.
If you 're going to use these implementations, at least mention my
name or something and notify me so I may even put a link on my page.
This implementation is freeware and according to the coderpunks'
manifesto it should remain so, so don 't use these implementations
in commercial applications.  Encryption, as a tool to ensure privacy
should be free and accessible for anyone.  If you plan to use these
implementations in a commercial application, contact me before
doing so.  If any algorithm is patented in your country, you should
acquire a license before using this software.  Modified versions of this
software must remain in the public domain and must contain an
acknowledgement of the original author (=me).
This implementaion is available at
http://ace.ulyssis.student.kuleuven.ac.be/~triade/GInt/index.htm


copyright 1999, Walied Othman
This header may not be removed.}

Unit RSA;

Interface

Uses Windows, SysUtils, Controls, GInt;

Procedure RSAEncrypt(P : String; exp, modb : TGInt; Var E : String);
Procedure RSADecrypt(E : String; exp, modb : TGInt; Var D : String);


Implementation


{$H+}




// Encrypt a string with the RSA algorithm, P^exp mod modb = E

Procedure RSAEncrypt(P : String; exp, modb : TGInt; Var E : String);
Var
   i, j, modbits : longint;
   PGInt, temp : TGInt;
   tempstr1, tempstr2, tempstr3 : String;
Begin
   GInttobinstr(modb, tempstr1);
   modbits := length(tempstr1);
   convert8to1bit(P, tempstr1);
   tempstr1 := '111' + tempstr1;
   j := modbits - 1;
   While (length(tempstr1) Mod j) <> 0 Do tempstr1 := '0' + tempstr1;

   j := length(tempstr1) Div (modbits - 1);
   tempstr2 := '';
   For i := 1 To j Do
   Begin
      tempstr3 := copy(tempstr1, 1, modbits - 1);
      While copy(tempstr3, 1, 1) = '0' Do delete(tempstr3, 1, 1);
      binstrtoGInt(tempstr3, PGInt);
      delete(tempstr1, 1, modbits - 1);
      GIntModExp(PGInt, exp, modb, temp);
      GIntDestroy(PGInt);
      tempstr3 := '';
      GInttobinstr(temp, tempstr3);
      While (length(tempstr3) Mod modbits) <> 0 Do tempstr3 := '0' + tempstr3;
      tempstr2 := tempstr2 + tempstr3;
      GIntdestroy(temp);
   End;

   While Not (tempstr2[1] = '1') Do delete(tempstr2, 1, 1);
   Convert1to8bit(tempstr2, E);
End;


// Decrypt a string with the RSA algorithm, E^exp mod modb = D

Procedure RSADecrypt(E : String; exp, modb : TGInt; Var D : String);
Var
   i, j, modbits : longint;
   EGInt, temp : TGInt;
   tempstr1, tempstr2, tempstr3 : String;
Begin
   GInttobinstr(modb, tempstr1);
   modbits := length(tempstr1);
   convert8to1bit(E, tempstr1);
   While copy(tempstr1, 1, 1) = '0' Do delete(tempstr1, 1, 1);
   While (length(tempstr1) Mod modbits) <> 0 Do tempstr1 := '0' + tempstr1;

   j := length(tempstr1) Div modbits;
   tempstr2 := '';
   For i := 1 To j Do
   Begin
      tempstr3 := copy(tempstr1, 1, modbits);
      While copy(tempstr3, 1, 1) = '0' Do delete(tempstr3, 1, 1);
      binstrtoGInt(tempstr3, EGInt);
      delete(tempstr1, 1, modbits);
      GIntModExp(EGInt, exp, modb, temp);
      GIntDestroy(EGInt);
      tempstr3 := '';
      GInttobinstr(temp, tempstr3);
      While (length(tempstr3) Mod (modbits - 1)) <> 0 Do tempstr3 := '0' + tempstr3;
      tempstr2 := tempstr2 + tempstr3;
      GIntdestroy(temp);
   End;

   While Not (copy(tempstr2, 1, 3) = '111') Do delete(tempstr2, 1, 1);
   delete(tempstr2, 1, 3);
   Convert1to8bit(tempstr2, D);
End;


End.