I wonder what the bug is. Could it be a timing or electrical/power-usage side channel attack on the chip making it possible to extract its private/secret key? T

I wonder what the bug is. Could it be a timing or electrical/power-usage side channel attack on the chip making it possible to extract its private/secret key? The linked page near the bottom of the article seems to hint on that: "powerful and expensive computing power to calculate the secret key and special custom-made software for signing are also needed."