A method for encrypting a plain text to be encrypted contained in a plain text message, wherein the plain text message consists of the plain text to be encrypted and an associated data block not to be encrypted, and an associated method for decrypting first and second cipher text parts contained in a cipher text message, the method comprising:
- providing a reversible decomposition function that allocates a decomposition of the reversible decomposition function to the plain text to be encrypted in first and second plain text parts, wherein the cipher text message consists of the first and second cipher text parts and the non-encrypted associated data block, wherein the decrypting of each of the first and second cipher text parts involves an implicit novelty bit sequence serving as an additional source of novelty;
- providing at least one encryption function implicitly equipped with first fixed key material, wherein the at least one encryption function encrypts the plain text to be encrypted with the at least one encryption function by including a variable input bit sequence;
- providing at least one decryption function, belonging to the at least one encryption function, implicitly equipped with second fixed key material, which decrypts a cipher text generated with the encryption function by including the variable input bit sequence;
- encrypting the plain text to be encrypted contained in the plain text message by including the implicit novelty bit sequence and suppling the first and second cipher text parts;
- obtaining the first cipher text part using the second plain text part, the associated data block, and the implicit novelty bit sequence, concatenated in any sequence, as a first parameter of the at least one encryption function and the first plain text part as a first second parameter of the at least one encryption function;
- obtaining the second cipher text part using the first cipher text part as a second first parameter of the at least one encryption function and the second plain text part as a second parameter of the at least one encryption function;
- receiving, by the at least one decryption function, the cipher text message with the implicit novelty bit sequence and the non-encrypted associated data block;
- and
- performing the decrypting belonging to the encrypting of the first and second cipher text parts contained in the cipher text message the implicit novelty bit sequence and returning the plain text,
- wherein the first and second plain text parts are obtained by the decrypting of the first cipher text part, the second cipher text part, the associated data block and the implicit novelty bit sequence,
- wherein the second plain text part is obtained using the first and second cipher text parts as a first parameter and as a first second parameter of the at least one decryption function, and
- wherein the first plain text part is decrypted separately from the second plain text part using the second plain text part, the non-encrypted associated data block, and the implicit novelty bit sequence, concatenated in the sequence used in the encrypting, as a second first parameter of the at least one decryption function, and the first cipher text part, as a second parameter of the at least one decryption function, according to which the plain text is obtained from the first and second plain text parts by an inversion of the reversible decomposition function.