1. A biometric data item coding method intended for use in a coding device, wherein a database stores a number N of representatives of biometric data items, a representative of a biometric data item corresponding to a set of characteristics of said biometric data item, said method comprising the following steps: /a/ obtaining an acquired biometric data item; /b/ obtaining a transformed biometric data item by transforming said acquired biometric data item according to said set of characteristics; /c/ obtaining N deviation values by applying a comparison between the transformed biometric data item and the N representatives in the database; and /d/ obtaining the acquired biometric data item in encoded form by obtaining a representative vector for the acquired biometric data item, said representative vector having a number of components that is less than or equal to N, said components being determined relative to said N deviation values.