AES algorithm is a block symmetric encryption algorithm adopted as an encryption standard in USA. The secret key length of AES is 16 bytes (128 bit). The minimum data block length converted in one cycle is 16 bytes. The algorithm features modes allowing to encrypt data blocks multiple of 16 bytes in length and randomly sized data blocks. Algorithm’s symmetry means the use of one and the same encryption secret key either for direct, or for reverse conversion.
You can find a detailed description of AES algorithm on NIST website.
Two more AES-type algorithms are implemented in Guardant dongles: AES128_ENCRYPT, AES128_DECRYPT. These algorithms are identical to AES128 by their properties, except for the fact that the first can perform only direct conversion (encryption) and the second – reverse (decryption).
Besides, in Guardant API an AES algorithm with 256 bit key is also implemented. Unlike hardware algorithm AES128 it is implemented on the software level, i.e. is executed in the RAM and the processor and not in the dongle.