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EBICS Implementation Notes
##########################
.. warning::
This document summarizes and clarifies some aspects of the EBICS protocol
that are important to LibEuFin. Both version 3.0 and 2.5 are discussed here.
It is not a specification, and it does not replace the official EBICS specification.
EBICS Glossary
==============
.. glossary::
A004
Electronic signature process, used in H004, deprecated in H005 with EBICS 3.0.
A005
Electronic signature process. Used in H004 and H005.
A006
Electronic signature process. Used in H004 and H005.
BTF
*Business Transaction Formats.* Before EBICS 3.0, many different order types were
used for business-related messages. With EBICS 3.0, the more generic BTU and BTD
order types are used for all business-related messages.
EBICS
The *Electronic Banking Internet Communication Standard*.
ES
Electronic Signature. This abbreviation is commonly used in the context of EBICS.
The following signature classes are defined (in descending order from
strongest to weakest):
E
Single signature (German "Einzeln").
A
First signature.
B
Second signature.
T
Transport signature. Only used to verify authorized submission,
but not to verify the bank-technical authorization.
In H004 and H005, the ES of the bank is specified as a "planned feature" that
is not actually implemented yet. Thus banks in practice only use their
encryption key pair and authentication/identity key pair.
EDS
Distributed Electronic Signature. Allows multiple subscribers to authorize an existing order.
HEV
The *Host EBICS Version*. Queried by the client with an HEV request message.
Human Subscriber
See :term:`Subscriber`.
H004
Host protocol version 4. Refers to the XML Schema defined in *EBICS 2.5*.
H005
Host protocol version 5. Refers to the XML Schema defined in *EBICS 3.0*.
Host ID
Alphanumeric identifier for the EBICS Host. One EBICS server can
host multiple banks, and each bank is identified by the Host ID.
This concept is similar to Taler's merchant backend instance identifiers.
Partner ID
In German, this is called "Kunden ID" (= Customer ID).
One partner can have multiple "participants", which are identified by user IDs.
Practical example: A company has one Partner ID. Each person at the company
that can access the company's bank accounts gets their own User ID.
When the person is indirectly accessing the bank server (for example via
a client server application), an additional "System ID" is created for this
"technical subscriber". When there is no technical subscriber, the System ID
must be the same as the User ID. Usually the System ID is optional though.
The ``(partner, user, system)`` triple uniquely identifies a subscriber.
User ID
??
System ID
??
ISO 20022
*ISO 20022: Financial Services - Universal financial industry message scheme*. Rather important
standard for financial industry **business-related** messages. In contrast, EBICS takes
care of message transmission, segmentation, authentication, key management, etc.
The full catalogue of messages is `available gratis <https://www.iso20022.org/full_catalogue.page>`_.
Segmentation
EBICS implements its own protocol-level segmentation of business-related messages.
The segmentation can be seen as an alternative to the HTTP facilities of ``Accept-Ranges``.
The order data of an ebics message may not exceed 1 MB. The segmentation applies both
to requests and responses.
Subscriber
Entity that wishes to communicate with the financial institution via EBICS.
Subscribers can be *technical* or *human*. Technical subscribers are typically
a server in client-server applications, where the server talks to a financial institution
via EBICS.
Requests from technical subscribers have a ``SystemID`` in addition to a ``PartnerID``
and ``UserId``. A technical subscriber cannot sign a bank-technical request.
Technical Subscriber
See :term:`Subscriber`.
TLS
*Transport Layer Security*. All messages in EBICS are sent over HTTP with TLS.
In the current version of the standard, only server certificates are required.
VEU
Distributed Electronic Signature (from German "Verteilte Elektronische Unterschrift").
X002
Identification and authentication signature in H004 and H005.
Order Types
===========
BTD
**Only EBICS3.0+**. Business Transaction Format Download.
Administrative order type to download a file, described in more detail by the BTF structure
BTU
**Only EBICS3.0+**. Business Transaction Format Upload.
Administrative order type to upload a file, described in more detail by the BTF structure
C52
**Before EBICS 3.0**. Download bank-to-customer account report.
C53
**Before EBICS 3.0**. Download bank-to-customer statement report.
FUL
**Before EBICS 3.0, France**. File Upload. Mainly used by France-style EBICS.
FDL
**Before EBICS 3.0, France**. File Download. Mainly used by France-style EBICS.
HIA
Transmission of the subscriber keys for (1) identification and authentication and (2)
encryption within the framework of subscriber initialisation.
HPB
Query the three RSA keys of the financial institute.
HPD
Host Parameter Data. Used to query the capabilities of the financial institution.
INI
Transmission of the subscriber keys for bank-technical electronic signatures.
HCS
Change keys without having to send a new INI/HIA letter.
SPR
Suspend a subscriber. Used when a key compromise is suspected.
The following order types are, for now, not relevant for LibEuFin:
H3K
Send all three RSA key pairs for initialization at once, accompanied
by a CA certificate for the keys. This is (as far as we know) used in France,
but not used by any German banks. When initializing a subscriber with H3K,
no INI and HIA letters are required.
HVE
Host Verification of Electronic Signature. Used to submit an electronic signature separately
from a previously uploaded order.
HVD
Retrieve VEU state.
HVD
Retrieve VEU overview.
HVS
Cancel Previous Order (from German "Storno"). Used to submit an electronic signature separately
from a previously uploaded order.
Key Management
==============
RSA key pairs are used for three purposes:
1. Authorization of requests by signing the order data. Called the *bank-technical key pair*.
2. Identification/authentication of the subscriber. Called the *identification and authentication key pair*.
3. Decryption of the symmetric key used to decrypt the bank's response. Called the *encryption key pair*.
One subscriber *may* use three different key pairs for these purposes.
The identification and authentication key pair may be the same as the encryption key pair.
The bank-technical key pair may not be used for any other purpose..
MT940 vs MT942
==============
* MT942 contains *pre-advice*, in the sense that transactions in it might still change
or be reversed
* M942 contains the settled transactions by the end of the day
Standards and Resources
=======================
EBICS
-----
The EBICS standard documents are available at `<http://www.ebics.org>`_.
EBICS 3.0:
* The main EBICS 3.0 specification
(``2017-03-29-EBICS_V_3.0-FinalVersion.pdf``).
* Annex 1 specifies EBICS return codes, as EBICS doesn't use HTTP status codes directly
(``2017-03-29-EBICS_V_3.0_Annex1_ReturnCodes-FinalVersion.pdf``) .
* Annex BTF contains the registry of BTF codes.
DFÜ Agreement
-------------
The DFÜ Agreement is the set of standards used by the German Banking Industry Committee (Deutsche Kreditwirtschaft).
The following Annexes (also see the `DK Website <https://die-dk.de/zahlungsverkehr/electronic-banking/dfu-verfahren-ebics/>`_) are
relevant for implementing EBICS:
* Annex 1 is the EBICS specification
* (Annex 2 is deprecated)
* Annex 3 describes the data formats used by German banks within EBICS.
EBICS Compendium
----------------
The `EBICS Compendium <https://www.ppi.de/en/payments/ebics/ebics-compendium/>`_ has some additional info on EBICS.
It is published by a company that sells a proprietary EBICS server implementation.
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