Features of Interaction with the UDRM Common Encryption Key Server

Key Request Algorithm

The keys are requested by sets, by crypto_period_count pieces in each set. The crypto_period_index is the current UTC time in seconds divided by crypto_period_length.

Regardless of key_request_policy, the keys for the current and next crypto_period_index are present in the local cache. So, if crypto_period_count is 1, then at the execution beginning 2 requests to the key server will be made: first — with the current crypto_period_index, next — with the following.

When key_request_policy is equal to request_when_each_key_expires, new keys are requested at the end of each crypto period, regardless of crypto_period_length. For example, if crypto_period_count equals to 3 and the first request must be made for the crypto period 1, at the beginning of period 1 the keys will be requested for periods 1, 2, 3, and at the beginning of period 2 — for periods 2, 3, 4, etc.

When key_request_policy is equal to request_when_last_key_expires, new keys are requested when there is no key for the next period in the local cache. For example, if crypto_period_count equals to 3 and the first request must be made for crypto period 1, then at the beginning of period 1 the keys for periods 1, 2, 3 will be requested, at the beginning of period 2 there will be no requests to the key server, and at the beginning of period 3 the keys for periods 4, 5, 6 will be requested.