A method of identifying primitives for implementing a physical unclonable function providing a response representative of a device comprising a plurality of primitives coupled in pairs, said primitives being configured for being one-time programmable through application of a burning energy to said primitives, by selecting a subset of the pairs, assessing a difference between electrical characteristics values provided by primitives belonging to each pair of said subset, qualifying all pairs of primitives for which the assessed difference is higher than a reference threshold, and identifying said qualified pairs of primitives comprising programming at least one primitive of each pair of primitives for which the assessed difference is lower than said reference threshold, by applying a burning energy to said at least one primitive so as to differentiate qualified pairs of primitives from those that are not qualified.