For encrypting a string of data elements from a first value range, a respective data element is combined with a key element by a first computing operation. The resulting combination result may lie outside the first value range. From the combination result, an encrypted data element is then derived by a second computing operation that maps onto a second value range, for example printable 1-byte characters. Decryption is accomplished by combining the encrypted data element with the key element using an inverse computing operation to the second computing operation executed iteratively until a result of an iteration step lies within the first value range.