user3719857 user3719857 - 6 months ago 12
Java Question

BadPaddingException : Decryption error

I'm writing a program which takes as input from the console - the name of a zip file, name of a zip file to be made containing the (de/en)crypted files generated from the first zip and a file containing the public key. I get the exception when decrypting:

exception Exception in thread "main" javax.crypto.BadPaddingException: Decryption error
at sun.security.rsa.RSAPadding.unpadV15(RSAPadding.java:380)
at sun.security.rsa.RSAPadding.unpad(RSAPadding.java:291)
at com.sun.crypto.provider.RSACipher.doFinal(RSACipher.java:363)
at com.sun.crypto.provider.RSACipher.engineDoFinal(RSACipher.java:389)
at javax.crypto.Cipher.doFinal(Cipher.java:2165)
at com.Main.decrypt(Main.java:67)
at com.Main.main(Main.java:201)


Can't figure out why I get this exception?

Public key:

MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCE3pA746UfpC8sFk8ZJp0yupyJqj5jy6cjdxUYoP7mCm7c0mqQDeCcDNBYW2eSozCioPrH/9L+CDQEPLYakoem+jFnUKDH5+pru/0PJTJJF8Xh/ZT9eJlvsYBr1/qSfICf6RTs7kzwq9IuSZBw7/tfNEF9i0A8FVox6HOopXod1QIDAQAB


Private key:

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


The code for the program is bellow . Any help is wellcomed :)

package com;

import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;
import java.util.Enumeration;
import java.util.Scanner;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import java.util.zip.ZipOutputStream;

import javax.crypto.Cipher;
import org.bouncycastle.asn1.ASN1EncodableVector;
import org.bouncycastle.asn1.ASN1Integer;
import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.DERNull;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.asn1.DERSequence;
import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;

public class Main {

public final static int BUFFER_SIZE = 117;

public static void decrypt(String originalZipFileName, String newZipFileName, String privateKeyFileName) throws Exception {
byte[] buffer = new byte[128];

ZipFile originalZipFile = new ZipFile(originalZipFileName);
ZipOutputStream newZipFile = new ZipOutputStream(new FileOutputStream(newZipFileName));

Enumeration<? extends ZipEntry> zipEntries = originalZipFile.entries();

String privateKey = getKeyString(privateKeyFileName);
PrivateKey key = makePrivateKey(privateKey);

Cipher cipher = Cipher.getInstance("RSA");

cipher.init(Cipher.DECRYPT_MODE, key);


while(zipEntries.hasMoreElements()){

ZipEntry entry = zipEntries.nextElement();

ZipEntry copy = new ZipEntry(entry.getName());
newZipFile.putNextEntry(copy);

InputStream inputEntry = originalZipFile.getInputStream(entry);

while(inputEntry.read(buffer) != -1){
newZipFile.write(cipher.doFinal(buffer));
}

newZipFile.closeEntry();
inputEntry.close();
}
newZipFile.close();
originalZipFile.close();
}

public static void encrypt(String originalZipFileName, String newZipFileName, String publicKeyFileName) throws Exception{

byte[] buffer = new byte[BUFFER_SIZE];

ZipFile originalZipFile = new ZipFile(originalZipFileName);
ZipOutputStream newZipFile = new ZipOutputStream(new FileOutputStream(newZipFileName));

Enumeration<? extends ZipEntry> zipEntries = originalZipFile.entries();

String publicKey = getKeyString(publicKeyFileName);
PublicKey key = makePublicKey(publicKey);

Cipher cipher = Cipher.getInstance("RSA");

cipher.init(Cipher.ENCRYPT_MODE, key);


while(zipEntries.hasMoreElements()){

ZipEntry entry = zipEntries.nextElement();

ZipEntry copy = new ZipEntry(entry.getName());
newZipFile.putNextEntry(copy);

InputStream inputEntry = originalZipFile.getInputStream(entry);

while(inputEntry.read(buffer) != -1){
newZipFile.write(cipher.doFinal(buffer));
}

newZipFile.closeEntry();
inputEntry.close();
}
newZipFile.close();
originalZipFile.close();
}

public static String getKeyString(String fileName){

String key = new String();
try {
BufferedReader buf = new BufferedReader(new FileReader(fileName));
key = buf.readLine();
} catch ( IOException e) {
e.printStackTrace();
}

return key.trim();
}

public static PublicKey makePublicKey(String stored) throws GeneralSecurityException {
byte[] data = Base64.getDecoder().decode(stored);
X509EncodedKeySpec spec = new X509EncodedKeySpec(data);
KeyFactory fact = KeyFactory.getInstance("RSA");
return fact.generatePublic(spec);
}

public static PrivateKey makePrivateKey(String stored) throws GeneralSecurityException, Exception {
/*byte[] data = Base64.getDecoder().decode(stored);
PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(data);
KeyFactory fact = KeyFactory.getInstance("RSA");
return fact.generatePrivate(spec);*/

byte[] data = Base64.getDecoder().decode(stored);

ASN1EncodableVector v = new ASN1EncodableVector();
v.add(new ASN1Integer(0));
ASN1EncodableVector v2 = new ASN1EncodableVector();
v2.add(new ASN1ObjectIdentifier(PKCSObjectIdentifiers.rsaEncryption.getId()));
v2.add(DERNull.INSTANCE);
v.add(new DERSequence(v2));
v.add(new DEROctetString(data));
ASN1Sequence seq = new DERSequence(v);
byte[] privKey = seq.getEncoded("DER");

PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(privKey);
KeyFactory fact = KeyFactory.getInstance("RSA");
PrivateKey key = fact.generatePrivate(spec);

return key;

}

public static void main(String[] args) throws Exception {

Scanner scan = new Scanner(System.in);

System.out.println("Enter type of operation:");
String line = scan.nextLine();

if(line.equals("encrypt")){
System.out.println("Enter name of original ZIP file:");
String originalZipFileName = scan.nextLine();

System.out.println("Enter name of new ZIP file:");
String newZipFileName = scan.nextLine();

System.out.println("Enter name of file containg public key:");
String publicKeyFileName = scan.nextLine();

encrypt(originalZipFileName, newZipFileName, publicKeyFileName);
}

if(line.equals("decrypt")){
System.out.println("Enter name of original ZIP file:");
String originalZipFileName = scan.nextLine();

System.out.println("Enter name of new ZIP file:");
String newZipFileName = scan.nextLine();

System.out.println("Enter name of file containg private key:");
String privateKeyFileName = scan.nextLine();

decrypt(originalZipFileName, newZipFileName, privateKeyFileName);
}

}

}


PS: Updated
decrypt
method. Still gives same error.

public static void decrypt(String originalZipFileName, String newZipFileName, String privateKeyFileName) throws Exception {
byte[] buffer = new byte[128];

ZipFile originalZipFile = new ZipFile(originalZipFileName);
ZipOutputStream newZipFile = new ZipOutputStream(new FileOutputStream(newZipFileName));

Enumeration<? extends ZipEntry> zipEntries = originalZipFile.entries();

String privateKey = getKeyString(privateKeyFileName);
PrivateKey key = makePrivateKey(privateKey);

Cipher cipher = Cipher.getInstance("RSA");

cipher.init(Cipher.DECRYPT_MODE, key);


while(zipEntries.hasMoreElements()){

ZipEntry entry = zipEntries.nextElement();

ZipEntry copy = new ZipEntry(entry.getName());
newZipFile.putNextEntry(copy);


InputStream inputEntry = originalZipFile.getInputStream(entry);


while(inputEntry.read(buffer) != -1){
newZipFile.write(cipher.doFinal(buffer));
}

newZipFile.closeEntry();
inputEntry.close();
}
newZipFile.close();
originalZipFile.close();
}

Answer

Jozef is right.

When you create cipher with default parameters, it defaults to "RSA/ECB/PKCS1Padding". You should specify padding explicitly, if you don't like nasty surprises. Because other security providers might have different default parameters. And you never know in advance which security settings each specific JRE has.

So PKCS1 padding adds 11 bytes to your original data increasing it from 117 bytes to 128 bytes. You should take into account that these numbers are specific to 1024 bit RSA keys (which are marginally secure) and will be different for longer keys. Since you are loading the key from a file consider checking its length.

@Test
public void testPadding() throws Exception {
    SecureRandom random = SecureRandom.getInstance("SHA1PRNG");

    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
    keyGen.initialize(1024, random);
    KeyPair keyPair = keyGen.generateKeyPair();

    /* constant 117 is a public key size - 11 */
    byte[] plaintext = new byte[117];
    random.nextBytes(plaintext);

    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.ENCRYPT_MODE, keyPair.getPublic());
    byte[] ciphertext = cipher.doFinal(plaintext);
    System.out.println(plaintext.length + " becomes " + ciphertext.length);
}

This prints

117 becomes 128

And finally, consider using AES instead of RSA for file encryption.

So to fix the problem you need to use buffer of size public key length - 11 (117) for encryption and public key size (128) for decryption.

Change

outputFile.write(cipher.doFinal(buffer), 0, read);

to

outputFile.write(cipher.doFinal(buffer));

because buffer read is 117 bytes and size of doFinal result is 128 bytes.

Also you need to buffer input streams. When you are reading from file, it can be slow sometimes and then InputStream will read less data than buffer may contain. By using BufferedInputStream one ensures that there is enough data before read call returns. However, for decryption it's crucial to have the full block of data

InputStream inputEntry = new BufferedInputStream(originalZipFile.getInputStream(entry));