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10. Cryptographic Engine
10.1 Description
The Cryptographic Engine provides a dedicated hardware accelerator for AES-128 encryption based algorithms and
dedicated flash and RAM memory to handle device parameters such as encryption keys, with no read access possible.
The Cryptographic Engine improves the power efficiency of cryptographic operations and reduces the code size of the
software stack. Verifying the integrity of data such as the payload of downlink frames is important to guarantee a secure
communication. The message integration check (MIC) uses the AES-CMAC algorithm to calculate a hash. Implementing the
MIC calculation in software would jeopardize the confidentiality of the used key. The cryptographic engine provides a
hardware implementation of the AES-CMAC to internally calculate and check the MIC.
The status of cryptographic operations can be checked by either polling the internal status register or using an interrupt
service routine.
10.2 Cryptographic Keys Definition
The cryptographic keys are arranged into several groups, according to the function they serve, as shown in
Cryptographic Keys Usage and
be derived from other keys.
Table 10-1: Cryptographic Keys Usage and Derivation
Key Source/
Group Name
Dest. Index
Network
Application
LifeTimeEnc
LifeTimeInt
GpTransport
LR1121
User Manual
Rev 1.1
UM.LR1121.W.APP
Mar 2023
Derivation. The table summarizes the allowed uses of the keys and if some of the keys can
Key Name
2
NwkKey
3
AppKey
4
JSEncKey
5
JSIntKey
6
GpKEKey0
7
GpKEKey1
8
GpKEKey2
9
GpKEKey3
10
GpKEKey4
11
GpKEKey5
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Usage
CryptoProcessJoinAccept()
CryptoComputeAesCmac()
CryptoDeriveKey()
CryptoSetKey(...)
CryptoDeriveKey()
CryptoSetKey(...)
CryptoProcessJoinAccept()
(Decryption)
CryptoSetKey(...)
CryptoProcessJoinAccept()
(MIC Computation)
CryptoComputeAesCmac()
CryptoSetKey(...)
CryptoDeriveKey(...)
CryptoSetKey(...)
Any multicast Key
Table 10-1:
Derivation From
1
DKEY
1
DKEY
From Network &
Application
From Network &
Application
From any other Gp
Transport key or from
Application Key
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