Maxim Integrated MAX32665 - Figure 23-3. Block Cipher Block Diagram; Table 23-2. Symmetric Block Ciphers

MAX32665-MAX32668 User Guide
Maxim Integrated Page 433 of 457
Figure 23-3 is a block diagram of the block cipher accelerator and its interface to the CMDA.
Figure 23-3. Block Cipher Block Diagram
AHB BUS
CIPHER KEY
CRYPTOGRAPHIC
DMA
CONTROLLER
BLOCK CIPHER ACCELERATOR
AES_ KEY2
CIPHER_CTRL.src = 0b10
AES_ KEY3
CIPHER_CTRL.src = 0b11
CIPHER_KEY_[7:0]
CIPHER_CTRL.src = 0b1x
LOAD CIPHER KEY
CIPHER_CTRL.key
CIPHER DONE
CRYPTO_CTRL.cph_done=1
WRITE FIFO
SOURCE:CIPHER OUTPUT
CRYPTO_CTRL.wrsrc = 0b01
DMA DONE
CRYPTO_CTRL.dma_done=1
BLOCK CIPHER
ENGINE
READ FIFO
SOURCE:DMA
CRYPTO_CTRL.rdrsrc = 0b01
CIPHER
OUTPUT
INITIAL
VECTOR
The symmetric block ciphers encrypt or decrypt data in blocks. The block sizes for each cipher are shown in Table 23-2.
Table 23-2. Symmetric Block Ciphers
CIPHER
KEY SIZE
USED KEY BITS
EFFECTIVE STRENGTH
(NIST SP800-57)
BLOCK SIZE
TDEA
192-bits
CIPHER_KEY[167:0]
(168-bits)
112-bits
64-bits
AES-128
128-bits
CIPHER_KEY[127:0]
128-bits
128-bits
128-bits
AES-192
192-bits
CIPHER_KEY[191:0]
192-bits
192-bits
128-bits
AES-256
256-bits
CIPHER_KEY[255:0]
256-bits
256-bits
128-bits
The accelerator supports the block cipher modes approved by NIST SP800-38A.
• Electronic Code Book (ECB)
• Cipher Block Chaining (CBC)
• Cipher Feedback (CFB)
• Output Feedback (OFB)
• Counter (CTR)
In the simplest mode Electronic Code Book (ECB), each data block is simply encrypted or decrypted using the cipher. A side
effect of this is that identical data blocks will encrypt to the same ciphertext. Various modes of operation are used that
chain or feedback ciphertext from the previous block to seed the next encryption operation. This causes identical, plain-text
data blocks to encrypt to different ciphertexts.