Hi,
I write a simple encoder in python and Java; they do the same
computations, with the same inputs: however they won't produce the same
output.
Let me explain with code.
First of all, you need a test file for input:
$ dd if=/dev/urandom of=test.img bs=1048576 count=1
I have attached the code.
As you can see we have xor-red the same inputs (bitlists are the same,
thus the selected blocks to xor are the same - you can easily see it,
whenever a block is xor-red both programs will print out its hash).
But here comes the strange: the random_block that the
create_random_block function returns is not the same: in Java this block
has an hash which is different from the Python one.
Why?
Thank you
import os
import sha
import sys
class EncoderDecoder(object):
def create_random_block(self,piece,blocksize=16384):
if len(piece) % blocksize != 0:
raise Exception('size error')
self.N = len(piece)/blocksize
random_block = ['0']*blocksize
bitlist = [1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1,
1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1,
1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0, 1]
for i in range(len(bitlist)):
if bitlist[i] == 1:
block = piece[i*blocksize:i*blocksize+blocksize]
print '%d-%d %s'
%(i*blocksize,i*blocksize+blocksize,sha.new(block).hexdigest())
for j in range(blocksize):
random_block[j] = chr(ord(random_block[j]) ^ ord(block[j]))
print sha.new(''.join(random_block)).hexdigest()
return ''.join(random_block)
if __name__ == '__main__':
data = open('test.img','rb').read()
x = EncoderDecoder()
x.create_random_block(data)
sys.exit(0)
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
public class Test {
int N;
public byte[] create_random_block(byte[] piece)
throws NoSuchAlgorithmException,
UnsupportedEncodingException {
N = piece.length / 16384;
byte[] random_block = new byte[16384];
int[] bitlist = { 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1,
1, 1, 0,
0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0,
1, 1, 1, 0, 0,
1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1,
0, 1, 0, 0, 1,
0, 1, 0, 1 };
for (int i = 0; i < N; i++) {
if (bitlist[i] == 1) {
byte[] block = new byte[16384];
for (int j = 0; j < block.length; j++) {
block[j] = piece[i * 16384 + j];
}
System.out.println(i * 16384 + "-" + (i * 16384
+ 16384)
+ " " +
AeSimpleSHA1.SHA1(block));
for (int j = 0; j < random_block.length; j++) {
random_block[j] = (byte)
(random_block[j] ^ block[j]);
}
}
}
System.out.println(AeSimpleSHA1.SHA1(random_block));
return random_block;
}
public static void main(String[] args) throws IOException,
NoSuchAlgorithmException {
byte data[] = new byte[1024 * 1024];
FileInputStream fi = new FileInputStream("test.img");
fi.read(data);
Test x = new Test();
x.create_random_block(data);
System.exit(0);
}
public static class AeSimpleSHA1 {
private static String convertToHex(byte[] data) {
StringBuffer buf = new StringBuffer();
for (int i = 0; i < data.length; i++) {
int halfbyte = (data[i] >>> 4) & 0x0F;
int two_halfs = 0;
do {
if ((0 <= halfbyte) && (halfbyte <= 9))
buf.append((char) ('0' +
halfbyte));
else
buf.append((char) ('a' +
(halfbyte - 10)));
halfbyte = data[i] & 0x0F;
} while (two_halfs++ < 1);
}
return buf.toString();
}
public static String SHA1(byte[] text) throws
NoSuchAlgorithmException,
UnsupportedEncodingException {
MessageDigest md;
md = MessageDigest.getInstance("SHA-1");
byte[] sha1hash = new byte[40];
md.update(text);
sha1hash = md.digest();
return convertToHex(sha1hash);
}
}
}
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