Question

We’ve to implement an encryption for an external interface. The owner of the interface has given documentation of how to preform the same encryption on our side. However, this documentation is in C# and we work in PHP.

Most of the parts we understand except for where they seem to typecast a hash to an int. Their code reads:

// hashString exists and is a md5 a like string
int[] keyBuffer = new int[hashString.length];
for (int i=0; i<hashString.length; i++) {
    keyBuffer[i] = (int)hashString[i];
}

In PHP, when casting a letter as int, you get 0 (int). As we can’t imagine this is what the third party means, we believe C# does something else.

Does C# also cast to int 0, or possibly to a char?

Second, the original hashString is 320 long. This means the code will be creating an int which is 320 long?? In PHP you don’t have this idea of reserving memory as C# does here. But when we try to typecast a 320 long string to an int we get an int which is 19 ‘chars’ long.

Does C# also create a shorter int when typecasting a really long ‘number’ in a string?

Answer 1

You’re converting a char to int. A char is a UTF-16 code unit – an unsigned 16-bit integer (the range is [0, 65535]). You get that value, basically, widened to a 32-bit signed integer. So 'A' ends up as 65, for example, and the Euro symbol (U+20AC) ends up as 8364 (0x20ac).

As for your second part – you’re creating an int, you’re creating an int array. An yes, you’ll be creating an array with 320 elements.