ECB — AES electronic codebook mode encryption

The AES electronic codebook mode encryption (ECB) can be used for a range of cryptographic functions like hash generation, digital signatures, and keystream generation for data encryption/decryption. The ECB encryption block supports 128 bit AES encryption (encryption only, not decryption).

AES ECB operates with EasyDMA access to system Data RAM for in-place operations on cleartext and ciphertext during encryption. ECB uses the same AES core as the CCM and AAR blocks and is an asynchronous operation which may not complete if the AES core is busy.

AES ECB features:

128 bit AES encryption
Supports standard AES ECB block encryption
Memory pointer support
DMA data transfer

AES ECB performs a 128 bit AES block encrypt. At the STARTECB task, data and key is loaded into the algorithm by EasyDMA. When output data has been written back to memory, the ENDECB event is triggered.

AES ECB can be stopped by triggering the STOPECB task.

Shared resources

The ECB, CCM, and AAR share the same AES module. The ECB will always have lowest priority and if there is a sharing conflict during encryption, the ECB operation will be aborted and an ERRORECB event will be generated.

EasyDMA

The ECB implements an EasyDMA mechanism for reading and writing to the Data RAM. This DMA cannot access the program memory or any other parts of the memory area except RAM.

If the ECBDATAPTR is not pointing to the Data RAM region, an EasyDMA transfer may result in a HardFault or RAM corruption. See Memory for more information about the different memory regions.

The EasyDMA will have finished accessing the Data RAM when the ENDECB or ERRORECB is generated.

ECB data structure

Input to the block encrypt and output from the block encrypt are stored in the same data structure. ECBDATAPTR should point to this data structure before STARTECB is initiated.

Table 1. ECB data structure overview
Property	Address offset	Description
KEY	0	16 byte AES key
CLEARTEXT	16	16 byte AES cleartext input block
CIPHERTEXT	32	16 byte AES ciphertext output block

Registers

Table 2. Instances
Base address	Peripheral	Instance	Description	Configuration
0x4000E000	ECB	ECB	AES Electronic Code Book (ECB) mode block encryption

Table 3. Register Overview
Register	Offset	Description
TASKS_STARTECB	0x000	Start ECB block encrypt
TASKS_STOPECB	0x004	Abort a possible executing ECB operation
EVENTS_ENDECB	0x100	ECB block encrypt complete
EVENTS_ERRORECB	0x104	ECB block encrypt aborted because of a STOPECB task or due to an error
INTENSET	0x304	Enable interrupt
INTENCLR	0x308	Disable interrupt
ECBDATAPTR	0x504	ECB block encrypt memory pointers

INTENSET

Address offset: 0x304

Enable interrupt

Bit number				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
Id																																		B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	ENDECB										Write '1' to Enable interrupt for ENDECB event See EVENTS_ENDECB
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	ERRORECB										Write '1' to Enable interrupt for ERRORECB event See EVENTS_ERRORECB
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

INTENCLR

Address offset: 0x308

Disable interrupt

Bit number				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
Id																																		B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	ENDECB										Write '1' to Disable interrupt for ENDECB event See EVENTS_ENDECB
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	ERRORECB										Write '1' to Disable interrupt for ERRORECB event See EVENTS_ERRORECB
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

ECBDATAPTR

Address offset: 0x504

ECB block encrypt memory pointers

Bit number				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
Id				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	ECBDATAPTR										Pointer to the ECB data structure (see Table 1 ECB data structure overview)

Electrical specification

ECB Electrical Specification

Symbol	Description				Min.	Typ.	Max.	Units
t_ECB	Run time per 16 byte block in all modes					6		µs