rsa.java

RSA is an asymetric method to crypt message. You can use RSA to crypt the key session of symetric me

package rsa;

import java.math.BigInteger;

public class RSA {
    
    public static String RSAES_OAEP_ENCRYPT(BigInteger n,BigInteger e,String M,String L){
        int mLen=M.length()/2;
        int hLen=20;
        int k=(int)((n.bitLength()+7)/8);
        if(mLen>k-2*hLen-2)return "Message too long";
        else{
            String EM=Codage.EME_OAEP_Coding(M,L,k,mLen);   
            BigInteger m=Primitives.OS2IP(EM);
            BigInteger c = Primitives.RSAEP (n,e,m);
            String C = Primitives.I2OSP (c, k);
            return C;
        }   
    }
    
    public static String RSAES_OAEP_DECRYPT (BigInteger n,BigInteger d,String C,String L){
        int cLen=C.length()/2;
        int hLen=20;
        int k=(int)((n.bitLength()+7)/8);
        if(cLen!=k ||(k<2*hLen+2)){
            return "Decryption Error";
        }else{
            BigInteger c = Primitives.OS2IP (C);
            BigInteger m = Primitives.RSADP (n,d, c);
            String EM = Primitives.I2OSP (m, k);
            String M=Codage.EME_OAEP_Decoding(EM,L,k);
            return M;
        }
    }
    
    public static String RSASSA_PSS_SIGN (BigInteger n,BigInteger d,String M,int sLen){
       int modBits=n.bitLength();
       int k=(modBits+7)/8;
       String EM=Codage.EMSA_PSS_ENCODE(M, modBits-1, sLen);
       BigInteger m = Primitives.OS2IP(EM);
       BigInteger s = Primitives.RSASP1 (n,d, m);
       String S = Primitives.I2OSP (s, k);
       return S;
    }
    
    public static String RSASSA_PSS_VERIFY (BigInteger n, BigInteger e, String M, String S,int sLen){
       int modBits=n.bitLength();
       int k=(modBits+7)/8;
       int tmp=S.length()/2;
       if(tmp!=k)return "Signature non valide";
       else{
           BigInteger s = Primitives.OS2IP (S);
           BigInteger m = Primitives.RSAVP1 (n, e, s);
           if(m==null)return "Signature non valide";
           else{
               int emLen=(modBits+6)/8;
               String EM = Primitives.I2OSP (m, emLen);
               String Result = Codage.EMSA_PSS_VERIFY(M, EM, modBits-1, sLen);
               if(Result.equals("consistent"))return "Signature valide";
               else return "Signature non valide!!!!!!!!!!!!!!!!!!!!!";
           }
       }
    }

}