decrypt By RSA Private Key - Android java.security

Android examples for java.security:RSA

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Description

decrypt By RSA Private Key

Demo Code


//package com.java2s;

import java.security.interfaces.RSAPrivateKey;

import javax.crypto.Cipher;

public class Main {

    public static String decryptByPrivateKey(String data,
            RSAPrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        // ??//from w  ww  .  j  a v  a 2  s.com
        int key_len = privateKey.getModulus().bitLength() / 8;
        byte[] bytes = data.getBytes();
        byte[] bcd = ASCII_To_BCD(bytes, bytes.length);
        System.err.println(bcd.length);
        // ???
        String ming = "";
        byte[][] arrays = splitArray(bcd, key_len);
        for (byte[] arr : arrays) {
            ming += new String(cipher.doFinal(arr));
        }
        return ming;
    }

    public static byte[] ASCII_To_BCD(byte[] ascii, int asc_len) {
        byte[] bcd = new byte[asc_len / 2];
        int j = 0;
        for (int i = 0; i < (asc_len + 1) / 2; i++) {
            bcd[i] = asc_to_bcd(ascii[j++]);
            bcd[i] = (byte) (((j >= asc_len) ? 0x00
                    : asc_to_bcd(ascii[j++])) + (bcd[i] << 4));
        }
        return bcd;
    }

    public static byte[][] splitArray(byte[] data, int len) {
        int x = data.length / len;
        int y = data.length % len;
        int z = 0;
        if (y != 0) {
            z = 1;
        }
        byte[][] arrays = new byte[x + z][];
        byte[] arr;
        for (int i = 0; i < x + z; i++) {
            arr = new byte[len];
            if (i == x + z - 1 && y != 0) {
                System.arraycopy(data, i * len, arr, 0, y);
            } else {
                System.arraycopy(data, i * len, arr, 0, len);
            }
            arrays[i] = arr;
        }
        return arrays;
    }

    public static byte asc_to_bcd(byte asc) {
        byte bcd;

        if ((asc >= '0') && (asc <= '9'))
            bcd = (byte) (asc - '0');
        else if ((asc >= 'A') && (asc <= 'F'))
            bcd = (byte) (asc - 'A' + 10);
        else if ((asc >= 'a') && (asc <= 'f'))
            bcd = (byte) (asc - 'a' + 10);
        else
            bcd = (byte) (asc - 48);
        return bcd;
    }
}

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