21. The system of claim 15 , wherein the receiving station is a multiple-printer system.
15. A system including at least two image processing devices, and adapted for secure transmission of digital data relating to a document between the at least two image processing devices, the system comprising: a sending station including: a user interface for inputting a session-specific user-defined character string by an operator, a key former for automatically forming an encryption key based on the user- defined character string, an encryption module for encrypting a document file to produce an encrypted document file, using the encryption key, while automatically leaving one or more predetermined specifying header items in the document file as unencrypted, a file former for forming a transmission file including the encrypted document file, and a transmitter for transmitting the transmission file towards a receiving station; and a receiving station including: a receiver for receiving the transmission file from the sending station, a storage unit for storing the received transmission file, a user interface for inputting a user-defined character string by an operator, a second key former for automatically forming a decryption key based on the input user-defined character string, and a decryption module for decrypting the encrypted document file to a decrypted document file, using the decryption key, wherein the sending station further includes: a module for forming an additional file containing metadata relevant for the document file but not including any decryption clue, the additional file having a first part and a second part, and wherein the encryption module also encrypts only one of the first and second parts of the additional file using the same encryption key used for encrypting the document file, and the additional file is included in the transmission file.