Hash Processor (Hash); Hash Introduction; Hash Main Features; Hash Functional Description - ST STM32F207 Series Reference Manual

RM0033
21

Hash processor (HASH)

This section applies only to STM32F21x devices.
21.1

HASH introduction

The hash processor is a fully compliant implementation of the secure hash algorithm
(SHA-1), the MD5 (message-digest algorithm 5) hash algorithm and the HMAC (keyed-hash
message authentication code) algorithm suitable for a variety of applications. It computes a
message digest (160 bits for the SHA-1 algorithm, 128 bits for the MD5 algorithm) for
messages of up to (2
messages by means of hash functions. HMAC algorithms consist in calling the SHA-1, or
MD5 hash function twice.
21.2

HASH main features

•
Suitable for data authentication applications, compliant with:
–
–
–
•
Fast computation of SHA-1, and MD5
•
AHB slave peripheral
•
32-bit data words for input data, supporting word, half-word, byte and bit bit-string
representations, with little-endian data representation only.
•
Automatic swapping to comply with the big-endian SHA1 computation standard with
little-endian input bit-string representation
• Automatic padding to complete the input bit string to fit modulo 512 (16 × 32 bits)
message digest computing
•
5× 32-bit words (H0 to H5) for output message digest, reload able to continue
interrupted message digest computation.
•
Corresponding 32-bit words of the digest from consecutive message blocks are added
to each other to form the digest of the whole message
• Automatic data flow control with support for direct memory access (DMA)
Note: Padding, as defined in the SHA-1 algorithm, consists in adding a bit at bx1 followed by N
bits at bx0 to get a total length congruent to 448 modulo 512. After this, the message is
completed with a 64-bit integer which is the binary representation of the original message
length.
For this hash processor, the quanta for entering the message is a 32-bit word, so an
additional information must be provided at the end of the message entry, which is the
number of valid bits in the last 32-bit word entered.
21.3

HASH functional description

Figure 1
64
– 1) bits, while HMAC algorithms provide a way of authenticating
FIPS PUB 180-2 (Federal Information Processing Standards Publication 180-2)
Secure Hash Standard specifications (SHA-1)
IETF RFC 1321 (Internet Engineering Task Force Request For Comments number
1321) specifications (MD5)
shows the block diagram of the hash processor.
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Hash processor (HASH)
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