Nonce Service

Generates a 256-bit random number derived from the startup states of a dedicated SRAM. The nonce service provides the user with the ability to strengthen the NRBG of the User Cryptoprocessor random bit generator by providing an alternate entropy source to use as additional seed data in its DRBG functions.

NONCE = KeyTree256(PUK, 0, PUFSEED)

Where, PUFSEED is a 256-bit conditioned true random output of the SRAM-PUF. PUK is a 256-bit device-generated nonce set in the factory.

To generate maximum entropy and forward and backward resistance, the SRAM-PUF is automatically power-cycled before generating the seed.

Table 1. Nonce Service Request
System Service Descriptor Bit Field	Value	Description
15:7	MBOXADDR[10:2]	Mailbox address. See Table 2.
6:0	21H	Nonce service command

The following table lists the Nonce Service Mailbox Format.

Table 2. Nonce Service Mailbox Format
Offset	Length (bytes)	Parameter	Direction	Description
0	32	NONCE	Output	Generated nonce