RSA PKCS#1 복호화,Padding 문제 해결

RSA PKCS#1 복호화,Padding 문제 해결

안드로이드 에서 RSA 복호화시 몇몇 문제들로 인해 분석한 내용 입니다.

java에서 PCKS#1 을 복호화 하려면 일반 PC java 에서는

import sun.security.util.DerInputStream;
import sun.security.util.DerValue;

2가지 라이브러리를 사용 하나 android 에서 사용이 안됩니다.

일단 아래  소스가 PKCS#1을 읽기 위한 소스 입니다. 아래 방식으로 읽어 들어 와야 합니다.

package com.arghosttown.arghosttown;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.security.spec.RSAPrivateCrtKeySpec;

/**
 * This code is inspired and taken over from net.auth.core:oauth
 * (albeit in a highly stripped variation):
 * <p/>
 * Source is from http://oauth.googlecode.com/svn/code/java/ which is licensed
 * under the APL (http://oauth.googlecode.com/svn/code/java/LICENSE.txt)
 * <p/>
 * All credits go to the original author (zhang)
 *
 * @author roland
 * @since 30/09/15
 */
public class PKCS1Util {

    private PKCS1Util() {
    }

    public static RSAPrivateCrtKeySpec decodePKCS1(byte[] keyBytes) throws IOException {
        DerParser parser = new DerParser(keyBytes);
        Asn1Object sequence = parser.read();
        sequence.validateSequence();
        parser = new DerParser(sequence.getValue());
        parser.read();

        return new RSAPrivateCrtKeySpec(next(parser), next(parser),
                next(parser), next(parser),
                next(parser), next(parser),
                next(parser), next(parser));
    }

    // ==========================================================================================

    private static BigInteger next(DerParser parser) throws IOException {
        return parser.read().getInteger();
    }

    static class DerParser {

        private InputStream in;

        DerParser(byte[] bytes) throws IOException {
            this.in = new ByteArrayInputStream(bytes);
        }

        Asn1Object read() throws IOException {
            int tag = in.read();

            if (tag == -1) {
                throw new IOException("Invalid DER: stream too short, missing tag");
            }

            int length = getLength();
            byte[] value = new byte[length];
            if (in.read(value) < length) {
                throw new IOException("Invalid DER: stream too short, missing value");
            }

            return new Asn1Object(tag, value);
        }

        private int getLength() throws IOException {
            int i = in.read();
            if (i == -1) {
                throw new IOException("Invalid DER: length missing");
            }

            if ((i & ~0x7F) == 0) {
                return i;
            }

            int num = i & 0x7F;
            if (i >= 0xFF || num > 4) {
                throw new IOException("Invalid DER: length field too big ("
                        + i + ")");
            }

            byte[] bytes = new byte[num];
            if (in.read(bytes) < num) {
                throw new IOException("Invalid DER: length too short");
            }

            return new BigInteger(1, bytes).intValue();
        }
    }

    static class Asn1Object {

        private final int type;
        private final byte[] value;
        private final int tag;

        public Asn1Object(int tag, byte[] value) {
            this.tag = tag;
            this.type = tag & 0x1F;
            this.value = value;
        }

        public byte[] getValue() {
            return value;
        }

        BigInteger getInteger() throws IOException {
            if (type != 0x02) {
                throw new IOException("Invalid DER: object is not integer"); //$NON-NLS-1$
            }
            return new BigInteger(value);
        }

        void validateSequence() throws IOException {
            if (type != 0x10) {
                throw new IOException("Invalid DER: not a sequence");
            }
            if ((tag & 0x20) != 0x20) {
                throw new IOException("Invalid DER: can't parse primitive entity");
            }
        }
    }
}

그리고 아래는 소스의 일부분 입니다,

여기서 pkey 가

String pkey=
        "MIIEowIBAAKCAQEAh6OvWa5vAWBTcSosC2AgRMKPb5V9xfBLhj24qIbRaTGMgppe" +
        "Ay5y86CuOqI5LQ0caF271815Po934SyxRxgoJtgqk9Zq27rf+5fqa8Dp1qBo+RSS" +
        "XuAD0bP0ddIRiIGuJZW4dm7Y95Z89zUzBeAnPM6LCiUc6GxQmWXG9LJK3MsuKw2W" +
        "pW7fevLyczfCrnGI8av9KPXr2o2m37HI5ZZibI1UKUmaiAwWAttjpgMKJ4yggMle" +
        "wZL6tlehKXgURj6i1HN7WGmjzDK7hRchGDXYozNjS403ZRLTwh0q++V1WC0nGv3B" +
        "WQl2U42oINOnn5UN+072NbqfyilexR//hb9tJQIDAQABAoIBAGI0lw7dhq1+aquy" +
        "lvUdgf+GxodJuyiHFId7RKlwA0qgf1VIIu02wi+2lK8LKU5/AaRmyUw0DqbHBUrZ" +
        "KvmIefm15Q3o3rF8mhL1KNsfb67fsWE2Dcv3cYxxOHvdvqgRDF9WCZpmI10Pbicm" +
        "M2z7oC0cdfrAaC+3zJtj3yrns+ArhX8xv2OGXXanWa+Urj6yalkFvopbojYIU0nE" +
        "wLJhR8PKoeKPrNMQNEkUmV7fLv3yIN1SJaiYkG4+h6Y5UlKF9B4wFhL2i7RZTssr" +
        "+6GoIWaKL1uUK64uxEE/duqKSYNnv6efxTqCoBO4KtFRQ2NHf/NckD4jnr8uGSGw"
의 키입니다. 

       byte[] bPrivateKey2 = Base64.decode(pkey.getBytes(),Base64.DEFAULT);

        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "BC");
        KeyFactory keyFactory2 = KeyFactory.getInstance("RSA");
        RSAPrivateCrtKeySpec privateKeySpec =PKCS1Util.decodePKCS1(bPrivateKey2);
        privateKey2 = keyFactory2.generatePrivate(privateKeySpec);
        cipher.init(Cipher.DECRYPT_MODE, privateKey2);
        byte[] bPlain2 = cipher.doFinal('해석할데이터를 집어 넣어주면 됩니다. ');
        String sPlain2 = new String(bPlain2);

        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "BC");

RSA/ECB/PKCS1Padding" 을 하지 않으면 


위처럼 쓰레기 패딩 데이터가 붙습니다,