Maximum likelihood soft decision decoding of linear block codes is addressed in this correspondance. A novel algorithm based on Chase-2 algorithm for the decoding of systematic binary block codes is detailed. A double re-encoding technique in place of the classical algebraic decoding for the computation of the candidate codeword list is the major innovation of the proposed algorithm. This approach has been successfully applied to systematic block codes that have a code rate equal to ½ and a parity check matrix composed of an invertible sub-matrix for the redundancy part. Simulation results show performance close to the optimum maximum likelihood decoding for an excellent trade-off between BER performance and computational complexity. Then, the challenging issue of designing a decoder for a specific family of binary block codes, called Cortex codes is also described. Three soft decoders for Cortex codes with lengths equal to 32, 64, and 128 and a code rate equal to 1/2 have been designed.Then, all the decoders were successively implemented onto an field-programmable gate array (FPGA) device. To our knowledge, they are the first efficient digital implementations of Cortex codes.