Computer-implemented method of performing format-preserving encryption of a data object of variable size

A computer-implemented method for performing format-preserving encryption and decryption of a data object in a first format, the data object having a variable size, the data object comprising a plurality of characters occurring in at least two sequences of text characters mutually separated by pre-defined format-defining characters of the first format,

• wherein the plurality of characters and the format-defining characters define at least one format property of the data object in the first format, the method comprising:
• converting at least one of:
• the at least two sequences of text characters and the format-defining characters;
• and
• the at least two sequences of text characters and the at least one format property to obtain an encoded set of data in a second format;
• encrypting the encoded set of data by use of an inner encryption algorithm and at least one of a tweak and a key, the inner encryption algorithm being capable of taking a variable size input and of outputting, as its output, an encrypted version of the variable size input, to obtain an encrypted set of data;
• deconverting the encrypted set of data to obtain a deconverted encrypted set of data in a third format, wherein the combined steps of converting, encrypting, and deconverting are format-preserving such that the third format fulfills the at least one format property of the data object in the first format;
• outputting the deconverted encrypted set of data as an encrypted version of the data object in the third format;
• wherein the output deconverted set of data in the third format has a different size than the input data object in the first format;
• wherein during decryption the data object in the third format is converted into the second format and subsequently decrypted using the same at least one of the tweak and the key used during encryption to obtain a decrypted set of data which is subsequently deconverted into the first format.

A computer-implemented method for performing format-preserving encryption and decryption of a data object in a first format having predefined format properties, the data object having a variable size, the method comprising:

• converting, by use of a first reversible converting algorithm, the data object to obtain a converted version of the data object in a second format;
• encrypting the converted version of the data object by use of an inner encryption algorithm and at least one of a tweak and a key, the inner encryption algorithm being capable of taking a variable size input and of outputting, as its output, an encrypted version of the variable size input, to obtain an encrypted version of the data object;
• deconverting, by use of a first reversible deconversion algorithm, the encrypted version of the data object to obtain a deconverted encrypted version of the data object in a third format, wherein the combined steps of converting, encrypting, and deconverting are format-preserving such that the third format fulfills the pre-defined format properties of the first format;
• outputting the deconverted encrypted version of the data object;
• wherein the first deconversion algorithm is different from a reversed version of the first converting algorithm;
• wherein the output deconverted encrypted version of the data object in the third format has a different size than the input data object in the first format;
• wherein during decryption the data object in the third format is converted into the second format using a second converting algorithm and subsequently decrypted using the same at least one of the tweak and the key used during encryption to obtain a decrypted data object which is subsequently deconverted using a second deconversion algorithm into the first format;
• wherein the second deconversion algorithm is an inverse of the first converting algorithm and the first deconversion algorithm is an inverse of the second converting algorithm.