The invention relates to a method of symmetric cryptography using a secret encryption key K which is a random finite sequence of symbols or which is a permutation of the symbols of an ordered set E, by which the sender of an encrypted message or data sends with cryptogram C an information called In in a public way, the public information In allowing to change the secret encryption key K for each message. This, in the aim to constitute a symmetric cryptosystem using disposable keys, the invention consisting of a device for manufacturing the key K and disposable keys, as defined below: - first, the encryption key K, if in the form of a random finite sequence of symbols, is first designed and constructed in such a way that it is the concatenation of a permutation p of an ordered set E,for example if K is a bit sequence such that K = 1010111, K is cut so that it is a permutation of elements of a set E, permutation of blocks of bits, which can for example be defined here by the ordered set E = {11 101 10}; an algebraic group structure (S e, o) is constructed by this way in which the elements of E are blocks of symbols that make up K, S e is the symmetric group of E, which is the set of all permutations of E, these permutations being defined by the bijections from E to E associated with these permutations, and o is the function composition, - secondly, the key K, called mother-key, which is in the form of a permutation p of blocks of symbols constructed as above, or in the form of a permutation p of symbols composing an ordered set E, is chosen so as to be composed of a large number of cycles whose lengths, defined by the number of elements of each cycle, do not have a common divisor: the set of the permutations { p 1, p 2,.., p j,..,p a} is then a cyclic subgroup G of S e, a is the least common multiple denoted LCM of the integers representing the lengths of the cycles, and p j is the bijection p o p ο.....ο p, i.e. the function composition iterated (j -1) times, - thirdly, for each message to be encrypted the message sender randomly chooses an integer j. This integer j is the information In communicated with cryptogram C to modify the mother-key K. The message sender, and the receiver when he receives the pair (C, j), then calculate their new encryption key K '. K' is the permutation p j belonging to the cyclic subgroup G of S e which is generated by p. K' can be concatenated if necessary. The calculation of K' is carried out by a function f ( j, p) with f the algorithm called { p a} → p j, which one is defined by: for each element i belonging to E taken successively according to the order defined on E, calculate p j (i) by the following: if i is the first element of one of the cycles C of p, then p j (i) = p r (i), with r ≡ j mod L and L the length of the cycle C to which i belongs. Else look for the cycle C k, whose first element is k in which i appears. By this way, we obtain the integer x such that p x (k) = i which is read in the cycle C k. Then calculate the remainder r of (j + x)/Lk, Lk being the length of cycle C k. We then obtain p j (i) = p r (k), with r ≡ (j + x)mod Lk. - first, the encryption key K, if in the form of a random finite sequence of symbols, is first designed and constructed in such a way that it is the concatenation of a permutation p of an ordered set E,for example if K is a bit sequence such that K = 1010111, K is cut so that it is a permutation of elements of a set E, permutation of blocks of bits, which can for example be defined here by the ordered set E = {11 101 10}; an algebraic group structure (S e, o) is constructed by this way in which the elements of E are blocks of symbols that make up K, S e is the symmetric group of E, which is the set of all permutations of E, these permutations being defined by the bijections from E to E associated with these permutations, and o is the function composition, - secondly, the key K, called mother-key, which is in the form of a permutation p of blocks of symbols constructed as above, or in the form of a permutation p of symbols composing an ordered set E, is chosen so as to be composed of a large number of cycles whose lengths, defined by the number of elements of each cycle, do not have a common divisor: the set of the permutations { p 1, p 2,.., p j,..,p a} is then a cyclic subgroup G of S e, a is the least common multiple denoted LCM of the integers representing the lengths of the cycles, and p j is the bijection p o p ο.....ο p, i.e. the function composition iterated (j -1) times, - thirdly, for each message to be encrypted the message sender randomly chooses an integer j. This integer j is the information In communicated with cryptogram C to modify the mother-key K. The message sender, and the receiver when he receives the pair (C, j), then calculate their new encryption key K '. K' is the permutation p j belonging to the cyclic subgroup G of S e which is generated by p. K' can be concatenated if necessary. The calculation of K' is carried out by a function f ( j, p) with f the algorithm called { p a} → p j, which one is defined by: for each element i belonging to E taken successively according to the order defined on E, calculate p j (i) by the following: if i is the first element of one of the cycles C of p, then p j (i) = p r (i), with r ≡ j mod L and L the length of the cycle C to which i belongs. Else look for the cycle C k, whose first element is k in which i appears. By this way, we obtain the integer x such that p x (k) = i which is read in the cycle C k. Then calculate the remainder r of (j + x)/Lk, Lk being the length of cycle C k. We then obtain p j (i) = p r (k), with r ≡ (j + x)mod Lk.