DigiDoc file formats: DDOC, BDOC, CDOC

Overview of the DigiDoc container formats supported in different ID-software versions and components can be found here. There is also a sample file for every format.

Below you can find the description and links to specification for all three formats used in Estonia.  

BDOC

BDOC is a new digital signature format that was created in order to replace the DDOC (DigiDoc) digital signature format that is specific to Estonia. This article provides information about the BDOC file format.

BDOC 2.1. Digital signature standard EVS 821:2014 (published 05.06.2014, available at Estonian Centre for Standardisation)

BDOC 2.1.2 format specification, .PDF (published 05.2014)

BDOC 1.0. Digital signature standard EVS 821:2009 (published 2009, valid until 05.06.2014, available at Estonian Centre for Standardisation)

DDOC

This format of digitally signed files is based on the ETSI TS 101 903 Standard that is called ‘XML Advanced Electronic Signatures (XAdES)’. The standard describes the structure of digitally signed documents on various levels of incorporation of additional validity verification information.

DigiDoc corresponds to the XAdES profile ‘XAdES-X-L’.
The respective profile allows the following signed attributes to be linked to a signature:

  • Certificate used for signing
  • Signing time
  • Signing location
  • Signer role or resolution
  • The signature contains the signer certificate validity information
  • OCSP response
  • OCSP server certificate

As a result of the given model, it is possible to check a signature corresponding to the XAdES-C-L profile without additional information – the person checking the signature must trust the issuer of the signer certificate and the OCSP validity confirmation server certificate. For example, in case of DigiDoc client this means that the respective certificates need to be located in the Windows certificate store.

The DigiDoc container includes the source files (the files that were signed) as well as the signatures that are related to the signed file(s). Also every signature contains the certificate, validity confirmation and the validity confirmation service certificate.

For files that match the above model, the DigiDoc system uses the .ddoc extension.

DigiDoc file format version policy

The version of the document format (.ddoc) determines the structure of the DigiDoc file. A new file format is implemented if changing the DigiDoc document structure is necessary because of international standards or compatibility with other digital signature systems. The changes to DigiDoc file format version are very rare.

The first version (1.0) of the DigiDoc file format was called SK-XML while the subsequent versions (1.1 and newer) are called DIGIDOC-XML. The version and the name can be seen in the header of the document as follows: <SignedDoc format="DIGIDOC-XML" version="1.1">.

Descriptions of different document formats

DIGIDOC-XML 1.4

Has never been in use.

DIGIDOC-XML 1.3

NB! DIGIDOC-XML 1.3 is the last official DigiDoc format.

DIGIDOC-XML 1.2

DIGIDOC-XML 1.1

 

CDOC

.CDOC is an extension, that is used to distinguish files encrypted in the DigiDoc format. The encrypted DigiDoc file format (ENCDOC-XML) is based on the international standard XML-ENC.

A CDOC file contains a single encrypted data file (XML document or some other binary file
(MS Word, Excel, PDF, RFT etc)), recipient certificate, encrypted key for the decryption of the data file (transport key), and other non-compulsory meta data. Data files are encrypted with AES encryption algorithm using a 128 bit key. One encrypted file can have several recipients (possible decrypters), and for this purpose each CDOC file contains the recipient certificates and transport keys for each recipient for data file decryption.

CDOC formatted files have total functional (encryption and decryption) support in CDigiDoc
(C-library)
and JDigiDoc (Java) libraries. In case of the NDigiDoc library (.NET) encryption and decryption are supported only with software tokens. CDOC functionality is not supported by the DigiDoc COM library as of version 3.6.

As of April 2012 the padding methods used for CDOC files have been modified. For more information please refer to CDOC file format documentation.


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