CHALLENGE-RESPONSE PROXIMITY VERIFICATION OF USER DEVICES BASED ON TOKEN-TO-SYMBOL MAPPING DEFINITIONS

An access server communicates with a video conference device and a user device. The access server and the user device may access known mappings, including a default mapping. Each mapping is configuredto map between tokens and symbols according to a distinct mapping relationship between the multi-bit tokens and the symbols. The access server instructs the video conference device to map an initialtoken to an initial symbol based on the default mapping and to transmit the initial symbol. The access server receives from the user device the initial token and a challenge mapping selected by the user device. The access server determines a challenge token that the challenge mapping maps to a challenge symbol, and instructs the video conference device to transmit the challenge symbol. The accessserver grants the user device access to an information carrying channel only if the challenge token is received from the user device. 接入服务器与视频会议设备和用户设备进行通信。该接入服务器和用户设备可以访问包括默认映射在内的已知映射。每个映射被配置为根据多位令牌和符号之间的不同映射关系在令牌和符号之间进行映射。该接入