A method for analyzing a binary-based application protocol of a network. The method includes obtaining conversations from the network, extracting content of a candidate field from a message in each conversation, calculating a randomness measure of the content to represent a level of randomness of the content across all conversation, calculating a correlation measure of the content to represent a level of correlation, across all of conversations, between the content and an attribute of a corresponding conversation where the message containing the candidate field is located, and selecting, based on the randomness measure and the correlation measure, and using a pre-determined field selection criterion, the candidate offset from a set of candidate offsets as the offset defined by the protocol.