Datasheet

Table Of Contents

• Type 3: Add a random number of clock cycles to data processing, subject to a maximum of 11/13/15

clock cycles for key sizes of 128/192/256 bits

• Type 4: Add random spurious power consumption during data processing

By default, all countermeasures are enabled. One or more of the countermeasures can be disabled by

programming the Countermeasure Type field in the Control A (CTRLA.CTYPE) register. The

countermeasures use random numbers generated by a deterministic random number generator

embedded in AES module. The seed for the random number generator is written to the RANDSEED

countermeasures reduces AES module’s throughput. In short, the throughput is highest with all the

countermeasures disabled. On the other hand, with all of the countermeasures enabled, the best

protection is achieved but the throughput is worst.

42.6.3 Galois Counter Mode (GCM)

GCM is comprised of the AES engine in CTR mode along with a universal hash function (GHASH engine)

that is defined over a binary Galois field to produce a message authentication tag. The GHASH engine

processes data packets after the AES operation. GCM provides assurance of the confidentiality of data

through the AES Counter mode of operation for encryption. Authenticity of the confidential data is

assured through the GHASH engine. Refer to the NIST Special Publication 800-38D Recommendation

for more complete information.

SAM D5x/E5x Family Data Sheet

AES – Advanced Encryption Standard

Datasheet

DS60001507E-page 1419