RM0319 datasheet(312/368 Pages) STMICROELECTRONICS

312 / 368 page

Security co-processor (C3)

RM0319

312/368

Doc ID 022640 Rev 3

The first 3 instructions are used for computing the HMAC of a message and work in the

same way. The last one is used for saving and restoring the context.

HMAC [MD5/SHA1] instructions

Each HMAC [MD5/SHA1] instruction is composed by 3 sub-instructions:

●

INIT

●

APPEND

●

END

INIT

The HMAC [MD5/SHA1] INIT instruction is 2 words long. This instruction is used to set the

Function and the Source Address Register for the HMAC key.

Bits ‘aa’ in the above table are used to set the algorithm to use and have the same encoding

as in the HASH INIT instruction (Table 105.).

Bits 15 to 0 in the first instruction word (cccc in Table 110.) represent the length in Bytes of

the key.

APPEND

The HMAC [MD5/SHA1] APPEND instruction is 2 words long. This instruction is used to set

the Source Address Register for the message and to start the computation of the HMAC.

The length of the message is encoded in the first instruction word, while the second word

represents the Source Address for the message.

Bits ‘aa’ in the above table are used to set the algorithm to use and have the same encoding

as in the INIT instruction (Table 110.).

Bits 15 to 0 in the first instruction word (cccc in Table 111) represent the Count in Bytes of

the input message.

Note:

The state of the HASH channel should be saved after an HMAC-APPEND instruction, if a

consecutive HMAC-APPEND instruction is to be executed. The consecutive APPEND

instruction should be executed after restoring the previously saved state of the channel. If

this process is not followed, the HASH channel will not respond to any further instructions as

it will become non-operational.

Table 110.

HMAC INIT Instruction bit encoding

Bit Encoding

xxxx 011a a00x xxxx cccc cccc cccc cccc

32 bit Source Address for the key

Table 111.

HMAC APPEND Instruction bit encoding

Bit Encoding

xxxx 011a a01x xxxx cccc cccc cccc cccc

32 bit Source Address for the message

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