SAMA5D3_14 Datasheet, PDF (1695/1840 Pages) ATMEL Corporation – ARM-based Embedded MPU

53.3 Product Dependencies
53.3.1 Power Management
The TDES may be clocked through the Power Management Controller (PMC), so the programmer must first configure
the PMC to enable the TDES clock.
53.3.2 Interrupt
The TDES interface has an interrupt line connected to the Advanced Interrupt Controller (AIC).
Handling the TDES interrupt requires programming the AIC before configuring the TDES.
Peripheral IDs
Instance
ID
TDES
44
53.4
Functional Description
The Data Encryption Standard (DES) and the Triple Data Encryption Algorithm (TDES) specify FIPS-approved
cryptographic algorithms that can be used to protect electronic data. The TDES bit in the TDES Mode Register
(TDES_MR) is used to select either the single DES or the Triple DES mode.
Encryption (enciphering) converts data to an unintelligible form called ciphertext. Decrypting (deciphering) the ciphertext
converts the data back into its original form, called plaintext. The CIPHER bit in the TDES Mode Register is used to
choose between encryption and decryption.
A DES is capable of using cryptographic keys of 64 bits to encrypt and decrypt data in blocks of 64 bits. This 64-bit key is
defined in the Key 1 Word Registers (TDES_KEY1WRx).
A TDES key consists of three DES keys, which is also referred to as a key bundle. These three 64-bit keys are defined,
respectively, in the Key 1, 2 and 3 Word Registers (TDES_KEY1WRx, TDES_KEY2WRx and TDES_KEY3WRx). In
Triple DES mode (TDESMOD set to 1), the KEYMOD bit in the TDES Mode Register is used to choose between a two-
and a three-key algorithm:
 In three-key encryption mode, the data is first encrypted with Key 1, then decrypted using Key 2 and then
encrypted with Key 3.
 In three-key decryption mode, the data is decrypted with Key 3, then encrypted with Key 2 and then decrypted
using Key 1.
 In two-key encryption mode, the data is first encrypted with Key 1, then decrypted using Key 2 and then encrypted
with Key 1.
 In two-key decryption mode, the data is decrypted with Key 1, then encrypted with Key 2 and then decrypted using
Key 1.
The input to the encryption processes of the CBC, CFB, and OFB modes includes, in addition to the plaintext, a 64-bit
data block called the initialization vector (IV), which must be set in the Initialization Vector Registers (TDES_IVRx). The
initialization vector is used in an initial step in the encryption of a message and in the corresponding decryption of the
message.
SAMA5D3 Series [DATASHEET] 1695
11121D–ATARM–03-Apr-14