Do you have to sign the NDA to use the CryptoAuthLib Firmware Library?
I was thinking that it should be possible to rewrite hal_samd21_i2c_asf.* and hal_samd21_timer_asf.* files using SoftI2CMaster as mentioned in 5 Porting Guide for CryptoAuthLib. Then build it in Atmel Studio 7 to get at least a random number and move from there...