Proyectos de Subversion Android Microlearning

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package com.cesams.twogetskills.library;
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import java.util.*;
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public abstract class RSA {
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	private static long  mo(long g, long l)
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	{
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		long result = g - (l * (long) Math.floor(g/l));
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		return result;
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	}
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	private static long powmod(long base, long exp, long modulus) {
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		 long accum = 1;
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		 int i = 0;
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		 long basepow2 = base;
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		 while ((exp >> i)>0)
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		 {
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			 if (((exp >> i) & 1) == 1)
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			 {
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				 accum = mo((accum * basepow2) , modulus);
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			 }
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			 basepow2 = mo((basepow2 * basepow2) , modulus);
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			 i++;
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		 }
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		 return accum;
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	}
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	public static String decode(String c, long d,  long n)
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	{
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		 String[] decryptarray = c.split(" ");
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		 //Each number is then decrypted using the RSA formula: block ^D mod N
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		 StringBuffer deencrypt = new StringBuffer();
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		 for (int u=0; u < decryptarray.length; u++)
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		 	{
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			 	if(decryptarray[u].equals("")) {
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			 		continue;
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			 	}
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			 	String resultmod = String.valueOf(powmod(Long.valueOf(decryptarray[u]), d, n));
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			 	deencrypt.append(resultmod.substring(1, resultmod.length() - 1));
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		 }
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		 String s = deencrypt.toString();
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		 StringBuffer resultd = new StringBuffer();
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		 for (int u=0;  u< s.length() ; u+=2)
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		 {
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			 String num = s.substring(u, u + 2);
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			 int i = Integer.valueOf(num) + 30;
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		     char ch  = (char) i;
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			 resultd.append(ch);
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		 }
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		 return resultd.toString();
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	}
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  public static String encode (String m, long e, long n) {
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  	Vector<String> array = new Vector<String>();
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  	 for (int i=0;  i<m.length(); i+=3) {
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  	   String tmpasci="1";
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  	   for (int h=0;  h<3; h++) {
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  		   String tmpstr = "";
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  		   if (i+ h < m.length()) {
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  			   int aux = m.charAt(i + h);
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  			   tmpstr =  String.valueOf(aux - 30);
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  			   if (tmpstr.length() < 2) {
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  				   tmpstr = '0' + tmpstr;
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  			   }
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  		   } else {
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  			   break;
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  		   }
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  		   tmpasci = tmpasci + tmpstr;
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  	  }
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  	   tmpasci = tmpasci +  '1';
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  	  array.add(tmpasci);
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  	 }
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  	 StringBuffer coded = new StringBuffer();
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  	 for (int k=0; k<array.size(); k++) {
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  		 long resultmod = powmod(Long.valueOf(array.elementAt(k)), e, n);
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  		 coded.append( String.valueOf(resultmod));
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  		 coded.append(" ");
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  	 }
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  	 return coded.toString();
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 	}
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}