CC2520 datasheet(97/133 Pages) TI

97 / 133 page

CC2520 DATASHEET

2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER

SWRS068 – DECEMBER 2007

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If the last block of plaintext is not 16 bytes long, only the required number of bits (from the MSB end) from

the encryption is used in the XOR operation.

The UCTR instruction performs counter mode decryption and is absolutely identical to the CTR instruction

because counter mode encryption and decryption are symmetrical operations.

26.7

CBC-MAC

The CBC-MAC instruction performs authentication.

Note that if M[1:0]=0 no authentication code is output. For other values of M[1:0] the number of

authentication bytes that are output is 2

M[1:0]+1. If M[2]=0 the plaintext data is prefixed with the value of C

expanded to 8 bits by concatenation of a 0 at the MSB end.

26.8

CCM / UCCM

The CCM instruction uses both CBC-MAC and CTR to perform both authentication and encryption. It

supports the CCM* mode of operation as specified in IEEE 802.14.5-2006 [2].

The authentication (CBC-MAC) part calculates a Message Integrity Code (MIC) over the address range A to

A+F+C-1. The resulting MIC is encrypted with CTR mode encryption using the counter value with index 0.

The encryption (CTR) part encrypts the address range A+F to A+F+C-1 using CTR mode encryption and

counter values with index 1 and up, and thus generates C bytes of ciphertext.

The output which is the concatenation of the ciphertext and the encrypted MIC is written to memory starting

at address E.

The UCCM instruction decrypts the ciphertext in the address range A+F to A+F+C-1 using CTR mode

decryption. A MIC is then generated in the same way as for the CCM instruction, and compared to the MIC

in the input data. The result of the MIC comparison is stored in the DPUSTAT register.

26.8.1 Inputs to the CCM and UCCM Instructions

The input parameters to the CCM and UCCM instructions are described in detail in Figure 38 and Figure 39

with notes on how they related to the terminology used in the IEEE 802.15.4 specifications.

CC2520 Datasheet(PDF) 97 Page - Texas Instruments