1. A system for introducing redundant binary data in a plurality of n.gtoreq.6 parallel one bit wide streams (106) into a medium and for extracting those binary data again therefrom while correcting for at most t.gtoreq.2 simultaneously erroneous ones of said serial streams, said system comprising: a plurality of k.gtoreq.2 data inputs (100) for receiving in parallel successive groups of k input data bits each; an encoding device (104) comprising first multiplication means for multiplying the k streams of data bits with a generator matrix [G(D)] of n rows by k columns, consisting of a (kxk) identity matrix and an (n-k)xk additional matrix, wherein all elements of [G(D)] are polynomials in D, the delay operator of a length of one bit cell, and are elements of a field F(D) consisting of all Laurent series having coefficients a.sub.i, and wherein all elements of the additional matrix are non-zero and at least one thereof is a polynomial with at least two terms; wherein the generator matrix [G(D)] is given by an (nxk) generator matrix of a minimum distance separable symbol correcting code defined in a Galois field GF(2.sup.m) in that the coefficients of the polynomial elements in [G(D)] are the binary elements of the binary representation of the corresponding elements a.sub.i of the Galois field GP(2.sup.m) of the generator matrix of the minimum distance separable code, wherein 2.sup.m .gtoreq.n-1 and a.sub.i is an element of GF(2.sup.m); said encoding device having n outputs for, in synchronism with the reception of a group of k data bits, outputting a corresponding group having k unmodified data bits together with (n-k) redundant code bits to said medium; a decoding device for implementing a parity check matrix [H(D)] given by [G(D)].multidot.[H(D)]=0 when all operations are executed in the field F(D), said decoding device comprising: a plurality of B decoder modules (112-120) each having respective second multiplication means for receiving said groups of n code bits in parallel for multiplying the received code bit streams by a respective secondary parity check matrix [H.sub.1..b..B (D)] of (n-k) rows by n columns, the result of each multiplication consisting in (n-k) parallel streams of syndrome bits, each of said (n-k) streams indicating a preliminary correction bit stream to an associated code bit channel while also corresponding to a respective one of the (n-k) rows, wherein the derivation of [H.sub.1..b..B (D)] from [H(D)] is done as follows: i. a set of B second elements is formed, each second element consisting of 2t channel indices, each combination of t channel indices being contained in at least one of said elements; ii. for each of said second elements a first intermediate matrix is formed [R.sub.1..b..B (D)] consisting of only those columns of [H(D)] that have indices equal to respective indices of code channels contained in said element; iii. for each of said second elements a second intermediate matrix [H.sub.1..b..B (D)] is formed by: EQU [H.sub.1..b..B (D)]=[R.sub.1..b..B (D)].sup.-1 [H(D)] iv. for each of said second elements a matrix [H.sub.1..b..B (D)] is formed by: EQU [H.sub.1..b..B (D)]=a.sub.L (D)[H.sub.1..b..B (D)], wherein a.sub.L (D) is the smallest common multiple of all the denominators of all matrix elements of all matrices [H.sub.1..b..B (D)], written as a.sub.L (D)=D.sup.f .multidot.E(D) wherein f is the lowest power in D of a.sub.L (D) having a non-zero coefficient; for each of said B decoder modules, a shift register module (122-130) of (n-k) bits wide for receiving said syndrome bit streams and storing a predetermined sequence length thereof; for each of said shift register modules, a syndrome detector (132-140) for detecting and enumerating any non-zero syndrome bit sequence in the corresponding shift register and producing a gating signal under control of detection of (o. .. t) non-zero syndrome bit sequences but otherwise a blocking signal; connected to an output of each of said shift register modules, an (n-k) bit wide syndrome gate (142-150) that is transmitting exclusively under control of the gating signal from the associated syndrome detector, but otherwise blocked; a cross-connection device (152) for sorting the syndrome bit streams transmitted through said syndrome gates according to the corresponding one of said n code bit channels; delay means together with third multiplying means (110) connected in parallel to said B decoder modules for receiving at least the non-redundant code bit streams from the medium and for introducing a delay that is equal to the delay incurred in said decoder modules and said shift register modules while also effecting a multiplication by the polynomial E(D); EXCLUSIVE-OR means (154) connected to outputs of said cross-connection device and of said delay means together with third multiplying means for correcting at least the non-redundant code bit streams with non-zero syndrome bit streams, and outputting the corrected code bit streams.