A method for the tamper-proof storing of data in an electronic store using a bidirectionally linked blockchain structure, wherein the method comprises the steps of: • providing the bidirectionally linked blockchain structure, • providing the data to be stored, • providing a first family of functions, which comprises a plurality of functions, wherein the functions differ by at least one first parameter and are uniquely identifiable using the first parameter of each, • generating an additional block to extend the blockchain structure, which block comprises the data to be stored and is intended to be bidirectionally linked to the last block of the blockchain structure, wherein the last block of the blockchain structure comprises stored data, • creating a first block-dependent bidirectional linking function for bidirectionally linking the last block to the additional block, wherein the creation of the first linking function comprises the steps of: ∘ calculating at least one first check value for the last and the additional blocks (110, 112) using the data stored in the last block and the data to be stored in the additional block, ∘ selecting a first function from the first family of functions depending on the first check value in accordance with a first unique assignment condition between the first parameter of the selected first function and the first check value, ∘ using the selected first function for creating the first block-dependent bidirectional linking function, • bidirectionally linking the last block to the additional block, wherein the bidirectional linking comprises the steps of: ∘ adding the first block-dependent bidirectional linking function to the last block, ∘ adding the first block-dependent bidirectional linking function to the additional block, • storing the blockchain structure extended by the additional block. • providing the bidirectionally linked blockchain structure, • providing the data to be stored, • providing a first family of functions, which comprises a plurality of functions, wherein the functions differ by at least one first parameter and are uniquely identifiable using the first parameter of each, • generating an additional block to extend the blockchain structure, which block comprises the data to be stored and is intended to be bidirectionally linked to the last block of the blockchain structure, wherein the last block of the blockchain structure comprises stored data, • creating a first block-dependent bidirectional linking function for bidirectionally linking the last block to the additional block, wherein the creation of the first linking function comprises the steps of: ∘ calculating at least one first check value for the last and the additional blocks (110, 112) using the data stored in the last block and the data to be stored in the additional block, ∘ selecting a first function from the first family of functions depending on the first check value in accordance with a first unique assignment condition between the first parameter of the selected first function and the first check value, ∘ using the selected first function for creating the first block-dependent bidirectional linking function, ∘ calculating at least one first check value for the last and the additional blocks (110, 112) using the data stored in the last block and the data to be stored in the additional block, ∘ selecting a first function from the first family of functions depending on the first check value in accordance with a first unique assignment condition between the first parameter of the selected first function and the first check value, ∘ using the selected first function for creating the first block-dependent bidirectional linking function, • bidirectionally linking the last block to the additional block, wherein the bidirectional linking comprises the steps of: ∘ adding the first block-dependent bidirectional linking function to the last block, ∘ adding the first block-dependent bidirectional linking function to the additional block, ∘ adding the first block-dependent bidirectional linking function to the last block, ∘ adding the first block-dependent bidirectional linking function to the additional block, • storing the blockchain structure extended by the additional block.