A new conception of strong symmetric-key block cipher of byte-oriented architecture has been presented. The application is intended as an initial step on the way at the end of which cryptography and steganography converge. The issue is that the encryption procedure should be able to turn a plaintext file into a cryptogram in the form of a file containing quite reasonable message but unrelated to the plaintext file. For example, we could want to convert a phone call representing the plaintext file into the cryptogram file being the photo of a spacecraft. After such action the cryptogram is quite different from classic cryptograms looking usually as outputs of random ASCII characters generator. The method of encryption presented here produces cryptogram files comprised of characters which belong to the set determined by the cryptographic key, using the operations of conversion between bases and substitution. In general, the cipher is redundant, i.e. the size of the cryptogram file is usually greater than that of the plaintext file.