A block cipher method and apparatus using round repetition for providing, from a plaintext message (10), a ciphertext message (50) and a global tag (52) is disclosed. The plaintext message is converted into a plurality of ordered plaintext blocks (11) which are successively processed during a round for computing:—a cryptogram (30) by encrypting input data (20) using a single cryptographic key, said cryptogram comprising a first segment (31) and a second segment (32)—a ciphertext block (51) by performing a first operation (41) using, as operands: said first segment (31) said current plaintext block (11) and said second segment (32). At each next round said input data is newly determined based on the current ciphertext block and an updated reproducible data. The ciphertext message is determined by concatenating the ciphertext blocks and the global tag by a second operation (42) using computed authentication local tags as operands.