A method, performed by a server, comprising: determining, in response to a request from a first device operated by a source user, that an identity authentication is to be performed for the source user; identifying a target user who is deemed to satisfy at least a preset condition, the target user being a user other than the source user, wherein the identifying the target user comprises: determining a set of one or more associated users of the source user based at least in part on historical user information of the source user; computing a set of one or more trust levels between the source user and the respective ones of the set of one or more associated users based at least in part on the historical user information of the source user and location information of the respective ones of the set of one or more associated users, wherein the historical user information of the source user comprises information associated with one or more communications between the source user and the respective ones of the set of one or more associated users; and selecting the target user from the set of one or more associated users based at least in part on the corresponding trust level between the source user and the target user; generating validation information to authenticate identity of the source user; sending the validation information to a second device operated by the target user; receiving a validation response from the first device operated by the source user; and performing identity authentication, including verifying whether the validation response received from the first device operated by the source user matches the validation information sent to the second device. determining, in response to a request from a first device operated by a source user, that an identity authentication is to be performed for the source user; identifying a target user who is deemed to satisfy at least a preset condition, the target user being a user other than the source user, wherein the identifying the target user comprises: determining a set of one or more associated users of the source user based at least in part on historical user information of the source user; computing a set of one or more trust levels between the source user and the respective ones of the set of one or more associated users based at least in part on the historical user information of the source user and location information of the respective ones of the set of one or more associated users, wherein the historical user information of the source user comprises information associated with one or more communications between the source user and the respective ones of the set of one or more associated users; and selecting the target user from the set of one or more associated users based at least in part on the corresponding trust level between the source user and the target user; determining a set of one or more associated users of the source user based at least in part on historical user information of the source user; computing a set of one or more trust levels between the source user and the respective ones of the set of one or more associated users based at least in part on the historical user information of the source user and location information of the respective ones of the set of one or more associated users, wherein the historical user information of the source user comprises information associated with one or more communications between the source user and the respective ones of the set of one or more associated users; and selecting the target user from the set of one or more associated users based at least in part on the corresponding trust level between the source user and the target user; generating validation information to authenticate identity of the source user; sending the validation information to a second device operated by the target user; receiving a validation response from the first device operated by the source user; and performing identity authentication, including verifying whether the validation response received from the first device operated by the source user matches the validation information sent to the second device.