Espressif ESP32 Technical Reference Manual page 598

24 RSA Accelerator (RSA)
24 RSA Accelerator (RSA)
24.1 Introduction
The RSA Accelerator provides hardware support for multiple precision arithmetic operations used in RSA asym-
metric cipher algorithms.
Sometimes, multiple precision arithmetic is also called "bignum arithmetic", "bigint arithmetic" or "arbitrary pre-
cision arithmetic".
24.2 Features
• Support for large-number modular exponentiation
• Support for large-number modular multiplication
• Support for large-number multiplication
• Support for various lengths of operands
24.3 Functional Description
24.3.1 Initialization
The RSA Accelerator is activated by enabling the corresponding peripheral clock, and by clearing the DPORT_RSA_PD
bit in the DPORT_RSA_PD_CTRL_REG register. This releases the RSA Accelerator from reset.
When the RSA Accelerator is released from reset, the register RSA_CLEAN_REG reads 0 and an initialization
process begins. Hardware initializes the four memory blocks by setting them to 0. After initialization is complete,
RSA_CLEAN_REG reads 1. For this reason, software should query RSA_CLEAN_REG after being released from
reset, and before writing to any RSA Accelerator memory blocks or registers for the first time.
24.3.2 Large Number Modular Exponentiation
Large-number modular exponentiation performs Z = X
multiplication. Aside from the arguments X, Y , and M , two additional ones are needed — r and M
arguments are calculated in advance by software.
The RSA Accelerator supports operand lengths of N ∈ {512, 1024, 1536, 2048, 2560, 3072, 3584, 4096} bits. The
bit length of arguments Z, X, Y , M , and r can be any one from the N set, but all numbers in a calculation must
be of the same length. The bit length of M
To represent the numbers used as operands, define a base-b positional notation, as follows:
In this notation, each number is represented by a sequence of base-b digits, where each base-b digit is a 32-bit
word. Representing an N -bit number requires n base-b digits (all of the possible N lengths are multiples of
Espressif Systems
Y
mod M . The operation is based on Montgomery
'
is always 32.
32
b = 2
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. These
ESP32 TRM (Version 5.2)