RSA decrypt By Private Key - Android java.security

Android examples for java.security:RSA

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Description

RSA decrypt By Private Key

Demo Code


//package com.java2s;
import android.util.Base64;
import java.io.ByteArrayOutputStream;
import java.security.Key;
import java.security.KeyFactory;
import java.security.spec.PKCS8EncodedKeySpec;

import javax.crypto.Cipher;

public class Main {

    private static final int MAX_DECRYPT_BLOCK = 128;

    public static byte[] decryptByPrivateKey(byte[] encryptedData,
            String privateKey) throws Exception {
        byte[] keyBytes = Base64.decode(privateKey, Base64.DEFAULT);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");//Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, privateK);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;

        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet,
                        MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen
                        - offSet);/*ww w  .  ja v a2 s . c o m*/
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return decryptedData;
    }
}

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