A block cipher method using round repetition for providing, from a plaintext message, a ciphertext message and a global tag for authenticating said ciphertext message, said plaintext message being converted into a plurality of ordered plaintext blocks having a predefined bit length, each of said plaintext blocks being successively processed in an orderly manner as a current plaintext block during a round, said method comprising the following actions: - loading a first data into a register, - running said round by performing the following steps: - a first step for inputting input data into a block cipher algorithm, said input data comprising data of said register and a reproducible data, - a second step for computing, within said block cipher algorithm, a cryptogram by encrypting the input data using a single cryptographic key, said cryptogram comprising a first segment and a second segment, the latter being defined as an authentication local tag, - a third step for computing a ciphertext block by performing a first operation using, as operands, said first segment and said current plaintext block, - as long as all said plaintext blocks have not been processed in a round, reloading the register with said ciphertext block and applying an updating function to said reproducible data before running a new round by starting again to said first step, - determining said ciphertext message by concatenating the ciphertext blocks of all the rounds in said orderly manner, then - reloading the register with the last computed ciphertext block and applying said updating function to said reproducible data before performing only the first two steps of said round, then - computing said global tag by a second operation using all the computed authentication local tags as operands, characterized in that the third step of said round further uses said second segment as an operand. - loading a first data into a register, - running said round by performing the following steps: - a first step for inputting input data into a block cipher algorithm, said input data comprising data of said register and a reproducible data, - a second step for computing, within said block cipher algorithm, a cryptogram by encrypting the input data using a single cryptographic key, said cryptogram comprising a first segment and a second segment, the latter being defined as an authentication local tag, - a third step for computing a ciphertext block by performing a first operation using, as operands, said first segment and said current plaintext block, - as long as all said plaintext blocks have not been processed in a round, reloading the register with said ciphertext block and applying an updating function to said reproducible data before running a new round by starting again to said first step, - determining said ciphertext message by concatenating the ciphertext blocks of all the rounds in said orderly manner, then - reloading the register with the last computed ciphertext block and applying said updating function to said reproducible data before performing only the first two steps of said round, then - computing said global tag by a second operation using all the computed authentication local tags as operands,