41.4.7.1 Private Key Bus

The AESB features a private key internal register that can be accessed only through the dedicated private key bus from the TRNG.

The private key internal register cannot be read from any peripheral or from software.

The AESB key used by the encryption/decryption engine is either the private key internal register content or the AESB_KEYWRx registers content.

By default, after hardware reset, the AESB key is provided by the AESB_KEYWRx registers. The software can select the private key internal register by setting AESB_EMR.PKRS. The key stored in the AESB_KEYWRx registers remain available for later use by clearing AESB_EMR.PKRS.

Before selecting the private key internal register, the software must:

  1. Trigger the key transfer over the private key bus from the TRNG Key Bus host.
  2. Wait for completion of the transfer signaled in the TRNG Status register.
  3. Check for any access violation in AESB_WPSR.PKRPVS.
Figure 41-3. Key Selection