Texas Instruments SimpleLink CC2620 Technical Reference Manual page 809

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10.1.4.5 AES Engine
The composition of the AES core is the following:
• The main data path operates on the input block, performing the required substitution, shift, and mix
operations.
• The key scheduler generates the round keys. A new subkey is generated and XORed with the data
each round.
The AES key scheduler generates the round keys. During each round, a new subkey is generated from
the input key to be XORed with the data. Round keys are generated on-the-fly and parallel to data
processing to minimize register requirements. For encryption operations, the key sequencer transfers the
initial key data to the AES core. For decryption operations, the key scheduler must provide the final
subkey to the AES core so it can generate the subkeys in reverse order.
The AES core operates on the input block and performs the required substitution, shift, and mix
operations. For each round, the encryption core receives the proper round key from the AES key
scheduler. A fundamental component of the AES algorithm is the S-box. The S-box provides a unique
8-bit output for each 8-bit input.
The architecture of the AES decryption core is generally the same as the architecture of the encryption
core. One difference is that the generation of round keys for decryption requires an initial conversion of the
input key (always supplied by the host in the form of an encryption key) to the corresponding decryption
key. This conversion is done by performing a dummy encryption operation and storing the final round key
as a decryption key. The key scheduler is then reversed to generate the round keys for the decryption
operation. Consequently, for each sequence of decryption operations under the same key, a single
throughput reduction equal to the time to encrypt a single block occurs. When a decryption key is
generated, subsequent decryption operations with the same key use this generated decryption key
directly.
SWCU117C – February 2015 – Revised September 2015
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AES Cryptoprocessor Overview
Cryptography
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