C r y p t i o n, B p r o c e s s i n g

A E S D A T A E N C R Y P T I O N / D E C R Y P T I O N M O D U L E

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Decryption.

The DMA channel does not try a transfer when the F bit is clear. The DMA channel enters an idle state upon fetching a buffer descriptor with the F bit cleared.

When the F bit is modified by the device driver, the device driver must also write an ‘I’ to the CE bit (in the DMA Control register) to activate the idle channel.

D e c r y p t i o n

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During decryption, the expanded key must be fed to the AES core backwards. The hardware key expander can handle this, but the input key is different than for encryption. The key must be expanded and the last words must be written to the key buffer as shown:

A 128-bit key (K0, K1, K2, K3) is expanded to the following 32-bit word sequence: K0, K1, ..., K40, K41, K42, K43.

To expand the key backwards, the hardware key expander needs K40-K43.

A 192-bit key (K0, K1, K2, K3, K5, K6) is expanded to the following 32-bit word sequence: K0, K1, ..., K46, K47, K48, K49, K50, K51.

To expand the key backwards, the hardware key expander core needs K48-51 followed by K46-47.

A 256-bit key (K0, K1, K2, K3, K5, K6, K7) is expanded to the following 32-bit word sequence: K0, K1, ..., K52, K53, K54, K55, K56, K57, K58, K59.

To expand the key backwards, the hardware key expander core needs K56-59 followed by K52-55.

The hardware key expander recreates all the remaining words in backwards order.

E C B p r o c e s s i n g

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ECB mode does not require an initialization vector. Software just needs to set up a key buffer descriptor, followed by a data buffer descriptor.

Processing flow This is the ECB buffer descriptor processing flow: diagram

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NS9215 specifications

The Digi NS9215 is a powerful solution designed for industrial applications that require reliable connectivity and robust performance. Built on a foundation of advanced technologies, the NS9215 serves as a versatile networking device that meets the demands of automation, remote monitoring, and data acquisition.

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Digi NS9215 manual C r y p t i o n, B p r o c e s s i n g

Models: NS9215

D e c r y p t i o n

E C B p r o c e s s i n g

NS9215 specifications