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Retenciones
As of version 6.0 and above, FirmaSAT now supports the analysis and signing of Retenciones documents (Retenciones e información de pagos).
This works generally in the same way as for CFDi documents. Just pass the Retenciones file as input to the functions and FirmaSAT will deal with it.
To identify an XML file as a Retenciones document, use the
Get XML ReceiptVersion Number functions.
These will return 1010 for a Retenciones version 1.0 document
(yes, we know this makes the name of the function less appropriate, but we'll live with it).
Same information. Different names.
| CFDi | Retenciones | Comment |
|---|---|---|
certificado | Cert | X.509 certificate contents in base64 form |
noCertificado | NumCert | Serial number of X.509 certificate in 20-digit S.A.T. form |
sello | Sello | Signature in base64 form. Note lower- and upper-case letter 's' |
The big important difference is that the NumCert field is included in the signature for a Retenciones
document, but the equivalent noCertificado field was not included for CFDi documents.
This means that you must set the value of the NumCert field in your input XML document
before signing the file or computing the hash digest.
With a CFDi document you could set this to a 20-digit dummy value like "00000000000000000000" which would then be overwritten
by the SignXML function. With a Retenciones document, you have to set this to the correct value of
your signing certificate's serial number
before using the FirmaSAT functions.
To get the serial number from your .CER file use the Get Certificate Serial Number functions.
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This page last updated 15 August 2025
