ST STM32L4 5 Series Reference Manual page 859

RM0351
Example from FIPS PUB180-2
Let us assume that the original message is the ASCII binary-coded form of "abc", of length
L = 24:
byte 0
01100001 01100010 01100011 UUUUUUUU
<-- 1st word written to HASH_DIN -->
NBLW has to be loaded with the value 24: a "1" is appended at bit location 24 in the bit string
(starting counting from left to right in the above bit string), which corresponds to bit 31 in the
HASH_DIN register (little-endian convention):
01100001 01100010 01100011 1UUUUUUU
Since L = 24, the number of bits in the above bit string is 25, and 423 "0" bits are appended,
making now 448 bits.
This gives in hexadecimal (byte words in big-endian format):
61626380 00000000 00000000 00000000
00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000
00000000 00000000
The message length value, L, in two-word format (that is 00000000 00000018) is appended.
Hence the final padded message in hexadecimal (byte words in big-endian format):
61626380 00000000 00000000 00000000
00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000
00000000 00000000
If the hash processor is programmed to swap byte within HASH_DIN input register
(DATATYPE=10 in HASH_CR), the above message has to be entered by following below
the sequence:
1. 0xUU636261 is written to the HASH_DIN register (where
2. 0x18 is written to the HASH_STR register (the number of valid bits in the last word
written to the HASH_DIN register is 24, as the original message length is 24 bits).
3. 0x10 is written to the HASH_STR register to start the message padding (described
above) and then perform the digest computation.
4. The hash computing is complete with the message digest available in the HASH_Hx
registers (x = 0...4) for the SHA-1 algorithm. For this FIPS example, the expected value
is as follows:
HASH_H0 = 0xA9993E36
HASH_H1 = 0x4706816A
HASH_H2 = 0xBA3E2571
HASH_H3 = 0x7850C26C
HASH_H4 = 0x9CD0D89D
29.3.7 HMAC operation
Overview
As specified by Internet Engineering Task Force RFC2104, HMAC: keyed-hashing for
message authentication, the HMAC algorithm is used for message authentication by
irreversibly binding the message being processed to a key chosen by the user. The
algorithm consists of two nested hash operations:
byte 1 byte 2
00000000 00000018
DocID024597 Rev 5
byte 3
Hash processor (HASH)
'U' means don't care).
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