Method and system wherein that once the input data sequence (X) and the control block (K) have been supplied, the method and system generates always a sequence of randomized-encrypted data (A) which is an encrypted sequence of random numbers. The method and system randomize-encrypt the data sequence (X) in a corrective way generating the proposed randomized-encrypted text sequence (AP). The randomness verifier (603) validates the randomization of the proposed randomized-encrypted text sequence (AP). If the proposed randomized-encrypted text sequence (AP) is random, it is supplied as randomized-encrypted text sequence (A); if it is not random, the method and system randomize-encrypt the data sequence (X) in a different corrective way again. The iteration is repeated until it is encrypted and at random the proposed randomized-encrypted text sequence (AP).