54.5.16 AES GCM H Word Register x

This register can only be written if the WPEN bit is cleared in the AES Write Protection Mode Register.

Name:	AES_GCMHRx
Offset:	0x9C + x*0x04 [x=0..3]
Reset:	0x00000000
Property:	R/W


Bit	31	30	29	28	27	26	25	24
	H[31:24]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	23	22	21	20	19	18	17	16
	H[23:16]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	15	14	13	12	11	10	9	8
	H[15:8]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	7	6	5	4	3	2	1	0
	H[7:0]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0

Bits 31:0 – H[31:0] GCM H Word x

The four 32-bit H Word registers contain the 128-bit GCM hash subkey Hvalue.

Whenever a new key is written in AES_KEYWRx, two automatic actions are processed:

GCM hash subkey H generation
AES_GHASHRx Clear

If the application software requires a specific hash subkey, the automatically-generated H value can be overwritten in AES_GCMHRx. See Key Writing and Automatic Hash Subkey Calculation for details.

Generating a GCM hash subkey H by a write in AES_GCMHRx enables to:

select the GCM hash subkey H for GHASH operations,
select one operand to process a single GF128 multiply.