One or more implementations of the present specification provide cross-blockchain authentication. A subscribing client corresponding to a first blockchain and using a cross-chain client of a cross-blockchain interaction system, retrieves data from a second blockchain, where the data is published by a publishing client for use as an authentication data source, where the cross-blockchain interaction system comprises the subscribing client, the publishing client, and the cross-chain client, where the publishing client corresponds to the second blockchain, where the cross-chain client is separately interconnected with the subscribing client, and where the publishing client and the first blockchain are used as a sidechain that is anchored to the second blockchain, which is used as a main chain. Data to be authenticated is received from the second blockchain. The data to be authenticated is authenticated based on the authentication data source and a data authentication rule configured on the first blockchain.