1. A method for securely transmitting digital data relating to a document between a scanner, a printer and a host computer, interconnected by a digital network, the method comprising the steps of: at a sending station: generating a document file through a data source, receiving a session-specific user-defined character string from an operator, automatically forming an encryption key based on the user-defined character string, encrypting the 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, forming a transmission file including the encrypted document file, and transmitting the transmission file towards a receiving station; and at the receiving station: storing the received transmission file, receiving the same user-defined character string by from operator, automatically forming a decryption key based on the user-defined character string, and decrypting the encrypted document file to a decrypted document file, using the decryption key, the method further comprising: at the sending station: forming an additional file containing metadata relevant for the document file but excluding any decryption clue, the additional file having a first part and a second part, and encrypting only one of the first and second parts of the additional file, using the same encryption key used for encrypting the document file, wherein in the step of forming the transmission file, the additional file is included in the transmission file.
1. A method for securely transmitting digital data relating to a document between a scanner, a printer and a host computer, interconnected by a digital network, the method comprising the steps of: at a sending station: generating a document file through a data source, receiving a session-specific user-defined character string from an operator, automatically forming an encryption key based on the user-defined character string, encrypting the 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, forming a transmission file including the encrypted document file, and transmitting the transmission file towards a receiving station; and at the receiving station: storing the received transmission file, receiving the same user-defined character string by from operator, automatically forming a decryption key based on the user-defined character string, and decrypting the encrypted document file to a decrypted document file, using the decryption key, the method further comprising: at the sending station: forming an additional file containing metadata relevant for the document file but excluding any decryption clue, the additional file having a first part and a second part, and encrypting only one of the first and second parts of the additional file, using the same encryption key used for encrypting the document file, wherein in the step of forming the transmission file, the additional file is included in the transmission file. 10. The method of claim 1 , wherein the receiving station is a printer having a local user interface for inputting, by an operator, the character string used to form the decryption key.