Question

I can’t find a useful answer for this in relation to Java here or on the web in general. The problem is seemingly simple – I need a way of counting the number of bits contained in a byte array of arbitrary size. The byte array can hold hex, decimal or binary values.

I’m sure this is one of those questions that will have me kicking myself when I see an answer, but it’s proving extremely frustrating. The method should look something like:

public int bitsInByteArray(byte[] b) {
    return - sum of bit count (ie the sum total bits, not the sum of their values) 
    of each byte in b
}

Any direction or advice would be immensely appreciated.

EDIT – Apologies guys, I didn’t word this right at all. I’m doing a crypto assignment, and have been asked to “encrypt a single block containing 64 zero bits using AES with the key k”
Now, I created
byte[] zeroBlockAes = {0x0,0x0…0x0} until it contains 64 zero elements.
The problem is, this is a 512 bits surely? So should I just put eight zero values in?

When I do this, my encrypted output is
-75 111 69 107 -18 88 51 89 68 -123 -49 18 -26
-109 94 21

And when I decrypt again I get my original eight zeros. Is this normal in AES or am I possibly doing something wrong, I thought block ciphers produced the same size input / output for both encryption and decryption.

Answer 1

Given that 1 byte equals 8 bits, which Java defines in Byte.SIZE, we can write:

 public int bitsInByteArray(final byte[] b) {
     return b.length * Byte.SIZE;
 }