A Python interface to FirmaSAT

This is a Python interface to the core FirmaSAT library

FirmaSAT enables you to analyze and sign CFDi digital tax vouchers (Comprobantes Fiscal Digitales) as specified by the Servicio de Administración Tributaria (SAT) in Mexico.

FirmaSAT must be installed on your system. It is available from https://www.cryptosys.net/firmasat/.

Classes

Sello

Operates on the Sello (signature) node in a SAT XML document.

Tfd

Operates on the Timbre Fiscal Digital (TFD) element, if present.

Pkix

PKI X.509 security utilities. Operates on private keys and X.509 certificates.

Xmlu

XML utilities. Operates on SAT-specific XML documents.

Gen

General info about the core library DLL, e.g. version number, compile date.

Err

Details of errors returned by the core library DLL.

All code in is one module firmasat.py for simplicity of distribution. All methods are static methods.

Errors

Most errors (missing files, invalid format) will result in a firmasat.Error exception, although some methods are more forgiving and will return a negative error code instead. Passing a bad argument type will result in an ArgumentError exception

Examples

To use in Python’s REPL:

>>> from firmasat import *
>>> Gen.version()
105028

If you don’t like import * and find firmasat a bit long to type each time, try

>>> import firmasat as fs
>>> fs.Gen.version()
105028

To sign a CFDI document, create the base XML file with all the required data except the following nodes

Sello=""
Certificado=""
NoCertificado="30001000000300023708"

You must add the 20-digit serial number of your signing certificate to the NoCertificado node. See below.

Then run the Sello.sign_xml() method with full paths to your key and cer files.

n = Sello.sign_xml('new.xml', 'base.xml', "emisor.key", password, "emisor.cer")

This creates a new file new.xml with the Sello and Certificado nodes completed.

Finding a certificate’s serial number

>>> firmasat.Pkix.query_cert('emisor.cer', 'serialNumber')
'30001000000300023708'

or using FirmaSAT from the command line

> firmasat NUMBERCERT emisor.cer
30001000000300023708

Tests

There is a series of tests in test_firmasat.py (source). You should find an example there of what you want to do.

These tests require a subdirectory work in the same folder which must contain all the required test files.

test
|   test_firmasat.py
|
\---work
    |   emisor.cer
    |   emisor.key
    |   <...all required test files>
    |
    \---tmp.XXXXXXXX
            <..temporary files...>

The test function creates a new temporary subdirectory each time, which is deleted automatically. If you want to keep this temp folder for debugging, then add the argument nodelete on the command line.

This structure is already set up in the distribution file, so unzip the file firmasat-x.x.x.zip and open a command-line prompt in the test subdirectory. You can do any of the following.

  1. python test_firmasat.py

  2. py.test -v

  3. Open the file test_firmasat.py using IDLE and select Run > Run Module (F5).

We’ve tested this using the Python 3.10.8 interpreter and IDLE, PyCharm 2020.3, and py.test.

System requirements

Windows platforms only. Python 3 must be installed on your system (at least 3.6). FirmaSAT v10.50 or above must also be installed.

Contact

For more information or to make suggestions, please contact us at http://www.cryptosys.net/contact/.

David Ireland
DI Management Services Pty Ltd
Australia
http://www.cryptosys.net/contact/
18 April 2023