byte[] to unsigned BigInteger?

Question

Motivation: I would like to convert hashes (MD5/SHA1 etc) into decimal integers for the purpose of making barcodes in Code128C. For simplicity, I prefer al

Answer 1

But (rusty CS here) am I correct that a byte array can always be interpreted in two ways: A: as a signed number B: as an unsigned number

What's more correct is that all numbers (by virtue of being stored in the computer) are basically a series of bytes, which is what a byte array is. It's not true to say that a byte array can always be interpreted as a signed or unsigned version of a particular numeric type, as not all numeric types have signed and unsigned versions. Floating point types generally only have signed versions (there's no udouble or ufloat), and, in this particular instance, there is no unsigned version of BigInteger.

So, in other words, no, it's not possible, but since BigInteger can represent an arbitrarily large integer value, you're not losing any range by virtue of its being signed.

As to your second question, you would need to append 0x00 to end end of the array, as the BigInteger constructor parses the values in little-endian byte order.