Method for encrypting a set of at least two indexed data items (A j), implemented by a server, the data (A j) being in the form of lists of elements each element of which belongs to a finite set (ε) of indexed symbols (x i) called an alphabet, the method being characterised in that the data (A j) are encrypted to form a protected set (LOCK (A 1,...,A N)), the step of encrypting and creating the protected set comprising the following steps: - the server randomly generates, for each data item (A j) in the base, a corresponding encoding function (F j), and - for each symbol (x i) of the alphabet (ε), o for each data item (A j), ■ if at least one element of the list that constitutes the data item is the symbol (x i) of the alphabet, the server determines the image of said symbol (x i) of the alphabet via the encoding function (F j) corresponding to the data item (A j) in order to obtain a codeword coordinate F j (x i) that is a function of the data item and of the symbol of the alphabet, ■ the server adds the codeword coordinate F j (x i) thereby obtained to an indexed set (S i) corresponding to the element of the alphabet (x i), the set having a predetermined cardinal (l), o then the server randomly re-indexes the elements of the indexed set (S i) corresponding to the symbol (x i) of the alphabet (ε), and o the server adds the indexed set (S i) corresponding to the symbol (x i) of the alphabet to the protected set (LOCK (A 1,...,A N)), and in that, for each symbol (x i) in the alphabet (ε), prior to the re-indexing step, the server completes the indexed set (S i) corresponding to the alphabet element (x i) with error-inducing points. - the server randomly generates, for each data item (A j) in the base, a corresponding encoding function (F j), and - for each symbol (x i) of the alphabet (ε), o for each data item (A j), ■ if at least one element of the list that constitutes the data item is the symbol (x i) of the alphabet, the server determines the image of said symbol (x i) of the alphabet via the encoding function (F j) corresponding to the data item (A j) in order to obtain a codeword coordinate F j (x i) that is a function of the data item and of the symbol of the alphabet, ■ the server adds the codeword coordinate F j (x i) thereby obtained to an indexed set (S i) corresponding to the element of the alphabet (x i), the set having a predetermined cardinal (l), o then the server randomly re-indexes the elements of the indexed set (S i) corresponding to the symbol (x i) of the alphabet (ε), and o the server adds the indexed set (S i) corresponding to the symbol (x i) of the alphabet to the protected set (LOCK (A 1,...,A N)), and in that, for each symbol (x i) in the alphabet (ε), prior to the re-indexing step, the server completes the indexed set (S i) corresponding to the alphabet element (x i) with error-inducing points. o for each data item (A j), ■ if at least one element of the list that constitutes the data item is the symbol (x i) of the alphabet, the server determines the image of said symbol (x i) of the alphabet via the encoding function (F j) corresponding to the data item (A j) in order to obtain a codeword coordinate F j (x i) that is a function of the data item and of the symbol of the alphabet, ■ the server adds the codeword coordinate F j (x i) thereby obtained to an indexed set (S i) corresponding to the element of the alphabet (x i), the set having a predetermined cardinal (l), ■ if at least one element of the list that constitutes the data item is the symbol (x i) of the alphabet, the server determines the image of said symbol (x i) of the alphabet via the encoding function (F j) corresponding to the data item (A j) in order to obtain a codeword coordinate F j (x i) that is a function of the data item and of the symbol of the alphabet, ■ the server adds the codeword coordinate F j (x i) thereby obtained to an indexed set (S i) corresponding to the element of the alphabet (x i), the set having a predetermined cardinal (l), o then the server randomly re-indexes the elements of the indexed set (S i) corresponding to the symbol (x i) of the alphabet (ε), and o the server adds the indexed set (S i) corresponding to the symbol (x i) of the alphabet to the protected set (LOCK (A 1,...,A N)),