All system components that require random numbers use the HMAC DRBG implementation from MbedTLS. HMAC DRBG is an HMAC-based Deterministic Random Bit Generator defined in NIST SP 800-90A with strict limits and recommendations on seed management and generation limits. The MbedTLS implementation of HMAC DRBG uses a Nonce in the seeding of the RNG in addition to values gathered from an entropy pool for a total of 48 bytes of entropy, safely above the minimum requirement of 32 bytes defined by NIST.
Each reseeding of the RNG allows cryptographically safe generation of 2^48 random values, which is well under the maximum number of random values needed by the system.
For example, an SED performing DoS communication will generate 2 or 3 values for the handshake, plus an additional 2 or 3 for key generation. In the secure data channel, one random value may be used for each MTU-sized packet. In total, this is potentially 3+3+17 random values for each 16KB message. To meet the requirement of supporting 2^32 messages, this comes to a conservative estimate of ~99E9 values, which is well under the HMAC DRBG limit of 281.5E12 (2^48).
Since there are 3 instances of the RNG (DTLS, SCUM, Masked AES), each SED is given 192 bytes of "entropy" to support 48 byte entropy seeds for each instance. One entropy pool is provided at provision time, where the entropy pool is compiled into the SED controller binary. A second entropy pool is given to the SED by the SSS during a successful registration. This run-time entropy pool replaces the provision-time one in all 3 RNG instances until deregistration. Upon de-registration, the SED returns to using the provision-time pool.
If an HMAC DRBG instance is asked for more than 2^48 values, it will attempt to reseed with the current entropy pool. However, the entropy pool keeps track of how many seed requests have been made. If more requests are made than is available in the pool (and more than is necessary for the message limit), the SED will cease to operate since it is outside of its required operating state.