LR1121
User Manual Rev 1.1
UM.LR1121.W.APP Mar 2023
101 of 130
Semtech
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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 Table 10-1:
Cryptographic Keys Usage and Derivation. The table summarizes the allowed uses of the keys and if some of the keys can
be derived from other keys.
Table 10-1: Cryptographic Keys Usage and Derivation
Group Name
Key Source/
Dest. Index
Key Name Usage Derivation From
Network 2 NwkKey
CryptoProcessJoinAccept()
CryptoComputeAesCmac()
CryptoDeriveKey()
CryptoSetKey(...)
DKEY
1
Application 3 AppKey
CryptoDeriveKey()
CryptoSetKey(...)
DKEY
1
LifeTimeEnc 4 JSEncKey
CryptoProcessJoinAccept()
(Decryption)
CryptoSetKey(...)
From Network &
Application
LifeTimeInt 5 JSIntKey
CryptoProcessJoinAccept()
(MIC Computation)
CryptoComputeAesCmac()
CryptoSetKey(...)
From Network &
Application
GpTransport
6 GpKEKey0
CryptoDeriveKey(...)
CryptoSetKey(...)
Any multicast Key
From any other Gp
Transport key or from
Application Key
7 GpKEKey1
8 GpKEKey2
9 GpKEKey3
10 GpKEKey4
11 GpKEKey5
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