The Atmel chips do not claim that they have implemented counter-measures for power analysis, etc. Power analysis on a key operation is a dangerous attack if pr

The Atmel chips do not claim that they have implemented counter-measures for power analysis, etc. Power analysis on a key operation is a dangerous attack if proper counter-measures are not taken. You can literally read off the 0/1 of each bit of the key as the key operation is underway if you monitor the power/timing. The NXP chips inside the yubikey claim to be hardened against several such attacks (although I have not confirmed). NXP is a cagey company. For example, I am a researcher, and I wanted to get the yubi-key's unlocked to write and test new u2f protocols on their hardware. They wouldnt sell me development keys, and claimed that the restriction was placed on them by NXP. I wrote half-a-dozen requests to the NXP people, and they never replied.