main.java

SHA512 is a hash function. You can use sha512 with an asymetric method to sign a document.

/*
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 */

package sha512;

/**
 *
 * @author mokaddem
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
       String test_message="";//abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu";
       for(int i=0;i<1000000;i++)test_message+="a";
       byte[]byte_message=test_message.getBytes();
       int message_length=test_message.length();
       int l=test_message.length()*8;
       int k=((896-1-l)%1024);
       if (k<0)k+=1024;
       int k8=(k-7)>>>3;
       int nombre_bytes=message_length+k8+1+16;
       
       byte normal[]=new byte[nombre_bytes];
       
       //on va remplir le tableau 
       System.arraycopy(byte_message, 0, normal, 0, message_length);
       normal[message_length]=(byte) (0x80);
       for(int i=1;i<=k8+12;i++)normal[message_length+i]=(byte)(0x00);
       for(int i=1;i<=4;i++)normal[message_length+k8+12+i]=(byte)( l>>>(8*(4-i)) );
       
       long [] in=new long [16];
       int s=0;
       long sha[]=new long[8];
       sha[0]=0x6a09e667f3bcc908L;
       sha[1]=0xbb67ae8584caa73bL;
       sha[2]=0x3c6ef372fe94f82bL;
       sha[3]=0xa54ff53a5f1d36f1L;
       sha[4]=0x510e527fade682d1L;
       sha[5]=0x9b05688c2b3e6c1fL;
       sha[6]=0x1f83d9abfb41bd6bL;
       sha[7]=0x5be0cd19137e2179L;
       
       
       for (int j=0;j<(nombre_bytes>>>7);j++){
            
            for(int i=0;i<16;i++){
          
                in[i]=  (long)normal[s++]<<56|((long)(normal[s++]&0xFF))<<48
                        |((long)normal[s++]&0xFF)<<40|((long)normal[s++]&0xFF)<<32
                        |((long)normal[s++]&0xFF)<<24|((long)normal[s++]&0xFF)<<16
                        |((long)normal[s++]&0xFF)<<8|((long)normal[s++]&0xFF);  
            }
            sha=sha512.sha_512 (sha,in); 
                       
         
       }  
       for (int m=0;m<8;m++) System.out.println(Long.toHexString(sha[m])+" ");  
           
    }
       
       
       
}