Robert Quattlebaum
fd9fcf53fe
Sometimes the host processor doesn't have a good way to generate high-quality random numbers suitable for cryptographic use. However, the NCP often has such capability. This Spinel feature allows the host processor to fetch high-quality random numbers from a TRNG that may be present on the NCP.
2.8 KiB
Feature: True Random Number Generation
This feature allows the host to have access to any strong hardware random number generator that might be present on the NCP, for things like key generation or seeding PRNGs.
Support for this feature can be determined by the presence of CAP_TRNG.
Note well that implementing a cryptographically-strong software-based true random number generator (that is impervious to things like temperature changes, manufacturing differences across devices, or unexpected output correlations) is non-trivial without a well-designed, dedicated hardware random number generator. Implementors who have little or no experience in this area are encouraged to not advertise this capability.
Properties
PROP 4101: PROP_TRNG_32
- Argument-Encoding:
L - Type: Read-Only
Fetching this property returns a strong random 32-bit integer that is suitable for use as a PRNG seed or for cryptographic use.
While the exact mechanism behind the calculation of this value is implementation-specific, the implementation must satisfy the following requirements:
- Data representing at least 32 bits of fresh entropy (extracted from the primary entropy source) MUST be consumed by the calculation of each query.
- Each of the 32 bits returned MUST be free of bias and have no statistical correlation to any part of the raw data used for the calculation of any query.
Support for this property is REQUIRED if CAP_TRNG is included in the
device capabilities.
PROP 4102: PROP_TRNG_128
- Argument-Encoding:
D - Type: Read-Only
Fetching this property returns 16 bytes of strong random data suitable for direct cryptographic use without further processing(For example, as an AES key).
While the exact mechanism behind the calculation of this value is implementation-specific, the implementation must satisfy the following requirements:
- Data representing at least 128 bits of fresh entropy (extracted from the primary entropy source) MUST be consumed by the calculation of each query.
- Each of the 128 bits returned MUST be free of bias and have no statistical correlation to any part of the raw data used for the calculation of any query.
Support for this property is REQUIRED if CAP_TRNG is included in the
device capabilities.
PROP 4103: PROP_TRNG_RAW_32
- Argument-Encoding:
D - Type: Read-Only
This property is primarily used to diagnose and debug the behavior of the entropy source used for strong random number generation.
When queried, returns the raw output from the entropy source used to
generate PROP_TRNG_32, prior to any reduction/whitening and/or mixing
with prior state.
The length of the returned buffer is implementation specific and should be expected to be non-deterministic.
Support for this property is RECOMMENDED if CAP_TRNG is included in the
device capabilities.