Figure 503. Ccm Encryption And Authentication Principle - ST STM32G4 Series Reference Manual

AES hardware accelerator (AES)
GMAC is similar to GCM, except that it is applied on a message composed only by plaintext
authenticated data (that is, only header, no payload).
Counter with CBC-MAC (CCM) principle
Legend
In Counter with cipher block chaining-message authentication code (CCM) mode, the
plaintext message is encrypted while a message authentication code (MAC) is computed in
parallel, thus generating the corresponding ciphertext and the corresponding MAC (also
known as tag). It is described by NIST in Special Publication 800-38C, Recommendation for
Block Cipher Modes of Operation - The CCM Mode for Authentication and Confidentiality.
CCM mode is based on AES in counter mode for confidentiality and it uses CBC for
computing the message authentication code. It requires an initial value.
Like GCM, the CCM chaining mode can be applied on a message composed only by
plaintext authenticated data (that is, only header, no payload). Note that this way of using
CCM is not called CMAC (it is not similar to GCM/GMAC), and its usage is not
recommended by NIST.
33.4.4 AES procedure to perform a cipher operation
Introduction
A typical cipher operation is explained below. Detailed information is provided in sections
starting from
The flowcharts shown in
library implements the AES algorithm. AES accelerates the execution of the AES-128 and
AES-256 cryptographic algorithms in ECB, CBC, CTR, CCM, and GCM operating modes.
Note: For more details on the cryptographic library, refer to the UM1924 user manual "STM32
crypto library" available from www.st.com.
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Figure 503. CCM encryption and authentication principle

B0
key key
Init
(Encrypt)
Plaintext block 1
Ciphertext block 1
Initialization
vector
Encrypt
input
output
XOR
Section 33.4.8: AES basic chaining modes (ECB,
Figure 504
Count 1 +1 Count 2
key
Encrypt Encrypt
Plaintext block 2
Ciphertext block 2
Encrypt
and Figure 505 describe the way STM32 cryptographic
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key
Encrypt
Plaintext block 3
Ciphertext block 3
Encrypt
Final TAG
CBC).
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