Base64 Decode not working correctly along with Cipher.Decrypt in android

Question

Here's a string :

String msg="dpbqNszFN2cpmtlzPi3myV9M1ctlkSIQD95ue+T+9rz13T+Pe/aLZ8Pd5geI+PhEM/b0UeRS1cAzKybQsKICTBhh3ke5Jjw6BHWGESJWBnUT54lAlTvzkgOxpQ5stBh2cPPSn3KLyKmXifr8ClbV5s1k3Gy5C7HitA5KLw7hRxAmIGSWQG7PaiLNEVRbgicNfJ7Ic7VIdGA/UA51vK8mpywIR2YQUDPv30ThGq4DuclaJ3X4aVWVj8VYChcfM+82sViVU8HO3DF9CCU4EIADNET503olxiDZBp7WMYmJvWq0KhhZXkLSY3QFmcSMX6IThtdKKCcZp6hu3TtC+7aP7Q==";

So the byte array is

[1] => 100     [2] => 112     [3] => 98     [4] => 113     [5] => 78     [6] => 115     [7] => 122 ..

Which should be decoded to

[ I used PHP base64_encode() for encoding into the above form & base64_decode() for getting this output ]

[1] => 118     [2] => 150     [3] => 234     [4] => 54     [5] => 204     [6] => 197      7] => 55     ...

But the problem I'm facing is that ( In android , Using Base64.decode(String) ) it's getting decoded to :

[118, -106, -22, 54, -52, -59, 55, 103, 41, -102, -39, 115, 62, 45, -26, -55, 95, 76, -43, -53, 101, -111, 34, 16, 15, -34, 110, 123, -28, -2, -10, -68, -11, -35, 63, -113, 123, -10, -117, 103, -61, -35, -26, 7, -120, -8, -8, 68, 51, -10, -12, 81, -28, 82, -43, -64, 51, 43, 38, -48, -80, -94, 2, 76, 24, 97, -34, 71, -71, 38, 60, 58, 4, 117, -122, 17, 34, 86, 6, 117, 19, -25, -119, 64, -107, 59, -13, -110, 3, -79, -91, 14, 108, -76, 24, 118, 112, -13, -46, -97, 114, -117, -56, -87, -105, -119, -6, -4, 10, 86, -43, -26, -51, 100, -36, 108, -71, 11, -79, -30, -76, 14, 74, 47, 14, -31, 71, 16, 38, 32, 100, -106, 64, 110, -49, 106, 34, -51, 17, 84, 91, -126, 39, 13, 124, -98, -56, 115, -75, 72, 116, 96, 63, 80, 14, 117, -68, -81, 38, -89, 44, 8, 71, 102, 16, 80, 51, -17, -33, 68, -31, 26, -82, 3, -71, -55, 90, 39, 117, -8, 105, 85, -107, -113, -59, 88, 10, 23, 31, 51, -17, 54, -79, 88, -107, 83, -63, -50, -36, 49, 125, 8, 37, 56, 16, -128, 3, 52, 68, -7, -45, 122, 37, -58, 32, -39, 6, -98, -42, 49, -119, -119, -67, 106, -76, 42, 24, 89, 94, 66, -46, 99, 116, 5, -103, -60, -116, 95, -94, 19, -122, -41, 74, 40, 39, 25, -89, -88, 110, -35, 59, 66, -5, -74, -113, -19]

As you can see , some characters ( which are not readable though) , are not getting decoded correctly. Edit(2) : bytes are signed in java and unsigned in PHP . Thanks @Jon and @Tony for clearing that idea. But the bug remains in my code.

Edit(1):

Code Segment:

KeyFactory fact = KeyFactory.getInstance("RSA");
BigInteger e=new BigInteger("65537");
BigInteger n=new BigInteger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
RSAPublicKeySpec keySpec=new RSAPublicKeySpec(n,e);
PublicKey pubKey = (PublicKey) fact.generatePublic(keySpec);
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, pubKey );
String msg="dpbqNszFN2cpmtlzPi3myV9M1ctlkSIQD95ue+T+9rz13T+Pe/aLZ8Pd5geI+PhEM/b0UeRS1cAzKybQsKICTBhh3ke5Jjw6BHWGESJWBnUT54lAlTvzkgOxpQ5stBh2cPPSn3KLyKmXifr8ClbV5s1k3Gy5C7HitA5KLw7hRxAmIGSWQG7PaiLNEVRbgicNfJ7Ic7VIdGA/UA51vK8mpywIR2YQUDPv30ThGq4DuclaJ3X4aVWVj8VYChcfM+82sViVU8HO3DF9CCU4EIADNET503olxiDZBp7WMYmJvWq0KhhZXkLSY3QFmcSMX6IThtdKKCcZp6hu3TtC+7aP7Q==";
byte[] bytes=msg.getBytes("UTF-8");
byte[] enc_bytes= Base64.decode(bytes,Base64.DEFAULT);
byte[]  dt = cipher.doFinal(enc_bytes);   
String code=new String(dt,"UTF-8");
System.out.println(code);

Cipher decrypted String comes out as ( At the second system.out )

05-10 21:05:27.501: I/System.out(11809): �ќ2`��H&��'Va�x�m��0G�����V�T�����)^����/|���BG,f_r    fK�B7?�a��n������Jl�y�yL���}��΂Ճ������JZj�+�|�-#ș%u�1�z�c�G��nl�5����HELLO HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 H

The Base64_encoded & signed data is "HELLO HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 HI1 H"

---

[Solved]

Huge thanks to @JonSkeet .

cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding"); removed all the junk data prefixed to it.

Answer 1

All looks fine to me - you just need to remember that bytes are signed in Java. So a value of -106 in Java corresponds to an unsigned value of 150. Once you bear that in mind, I think you'll see that all the values in PHP correspond to the values in Java.

Note that you ought to distinguish between bytes and characters. So when you say:

As you can see , some characters ( which are not readable though) , are not getting decoded correctly.

You actually mean some bytes... and there's no such concept as a "readable" byte.

EDIT: I see no sign that you've actually decrypted the data at all.

You're converting the still encrypted result of the base64 decoding into text using the platform default encoding:

String tmpr=new String(baser);

You shouldn't be doing that - you should be using baser as the cipher-text to decrypt.

It's not at all clear where the tmp value you're passing to doFinal comes from at all...

Answer 2

Your issue is one of sign. The first sample 'the should' is treating the output bytes as 8-bit unsigned. The Android version is treating them as signed bytes.

Is your code actually failing?

Edit

cipher.final() seems to be designed to finish decryption. Did you call cipher.update() first? See the example here, and look for update(...) stackoverflow.com/questions/3150830/android-encryption

Here's the Android Cipher documentation, for your convenience.

Answer 3

Try this on your byte array

byte[] bytes = Base64.decode(data, Base64.DEFAULT);
String string = new String(bytes, "UTF-8");