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 3130292827262524 
 H[31:24] 
Access R/WR/WR/WR/WR/WR/WR/WR/W 
Reset 00000000 
Bit 2322212019181716 
 H[23:16] 
Access R/WR/WR/WR/WR/WR/WR/WR/W 
Reset 00000000 
Bit 15141312111098 
 H[15:8] 
Access R/WR/WR/WR/WR/WR/WR/WR/W 
Reset 00000000 
Bit 76543210 
 H[7:0] 
Access R/WR/WR/WR/WR/WR/WR/WR/W 
Reset 00000000 

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.