Datasheet

Table Of Contents

42.6.3.1 GCM Operation

42.6.3.1.1 Hashkey Generation

• Configure CTRLA register as follows:

1. CTRLA.STARTMODE as Manual (Auto for DMAC)

2. CTRLA.CIPHER as Encryption

3. CTRLA.KEYSIZE as per the key used

4. CTRLA.AESMODE as ECB

5. CTRLA.CTYPE as per the countermeasures required.

• Set CTRLA.ENABLE

• Write zero to CIPLEN reg.

• Write the key in KEYWORD register

• Write the zeros to DATA reg

• Set CTRLB.Start.

• Wait for INTFLAG.ENCCMP to be set

• AES Hardware generates Hash Subkey in HASHKEY register.

42.6.3.1.2 Authentication Header Processing

• Configure CTRLA register as follows:

1. CTRLA.STARTMODE as Manual

2. CTRLA.CIPHER as Encryption

3. CTRLA.KEYSIZE as per the key used

4. CTRLA.AESMODE as GCM

5. CTRLA.CTYPE as per the countermeasures required.

• Set CTRLA.ENABLE

• Write the key in KEYWORD register

• Set CTRLB.GFMUL

• Write the Authdata to DATA reg

• Set CTRLB.START as1

• Wait for INTFLAG.GFMCMP to be set.

• AES Hardware generates output in GHASH register

• Continue steps 4 to 7 for remaining Authentication Header.

Note: If the Auth data is less than 128 bit, it has to be padded with zero to make it 128 bit aligned.

SAM D5x/E5x Family Data Sheet

AES – Advanced Encryption Standard

Datasheet

DS60001507E-page 1421