A method for user authentication based on keystroke dynamics is provided. The user authentication method includes receiving a keystroke input implemented by a user; separating a sequence of pressed keys into a sequence of bigrams having bigram names simultaneously with the user typing free text; collecting a timing information for each bigram of the sequence of bigrams; extracting a feature vector for each bigram based on the timing information; separating feature vectors into subsets according to the bigram names; estimating a GMM user model using subsets of feature vectors for each bigram; providing real time user authentication using the estimated GMM user model for each bigram and bigram features from current real time user keystroke input. The corresponding system is also provided. The GMM based analysis of the keystroke data separated by bigrams provides strong authentication using free text input, while user additional actions (to be verified) are kept at a minimum. The present invention allows to drastically improve accuracy of user authentication with low performance requirements that allows to implement authentication software for low-power mobile devices.