SLAA547C July 2013 – July 2021 MSP430FR5739
Software implementation uses a 64-bit key to encipher 64-bit blocks. The DES takes in a 64-bit key, where every eighth bit is used for parity. Therefore, the effective key length is 56 bits. 3DES uses three 64-bit keys and, therefore, has an effective key length of 168-bits.
The DES library functions make use of key structure of type des_ctx defined in the helper file. This structure stores the key schedule for both encrypt and decrypt functions.