Considering a blockchain protocol, it can be sometimes useful to have a proof that a certain transaction or state was applied to the blockchain, without actually involving this data in the blockchain. Such a structure can be realized by distributed ledger solutions where the identity of the nodes are well-known. One algorithm might be that miner or validator node creates a private - public key pairs as identity where the public key is written into the blockchain but the private key is kept secret. If a piece of data is signed by the private key, it can be made sure that this piece of information was in fact validated by the protocol. The algorithm might be fine-tuned and further improved in a way that not only a leader node signs the piece of data, but many others as well, like in case of a quorum consensus or at a two phase Nakamoto consensus, like at Tendermint. The piece of information can be assigned by a timestamp as well, in the sense of validating the exact block where the information was signed. It can be realized as generating a new identity, new private public key by the validator nodes at each round only for the given round.
