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AES Registers
687
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Advance Encryption Standard Accelerator (AES)
9.5.5 AES_AUTH_LENGTH Register (Offset = 0x5C) [reset = 0x0]
AES Authentication Data Length (AES_AUTH_LENGTH)
The AES Authentication Data Length (AES_AUTH_LENGTH) register stores the authentication data
length in bytes for combined modes only (GCM or CCM). Supported AUTH lengths for CCM are from 0 to
(2
16
- 28) bytes. For GCM any value up to (2
32
- 1) bytes can be used. Once processing with this context is
started, this length decrements to zero. A write to this register triggers the engine to start using this
context for GCM and CCM. For XTS, this register is optionally used to load j. Loading of j is only required
if j ≠0. j is a 28-bit value and must be written to bits [31-4] of this register. j represents the sequential
number of the 128-bit block inside the data unit. For the first block in a unit, this value is zero. It is not
required to provide a j for each new data block within a unit. Note that it is possible to start with a j
unequal to zero.
NOTE:
For a Host read operation, these registers return all zeroes.
AES_AUTH_LENGTH is shown in
and described in
Return to
Figure 9-18. AES_AUTH_LENGTH Register
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
AUTH
R/W-0x0
Table 9-12. AES_AUTH_LENGTH Register Field Descriptions
Bit
Field
Type
Reset
Description
31-0
AUTH
R/W
0x0
Authentication Data Length.
This field stores the authentication data length in bytes for combined
modes (GCM or CCM).