Glossary
e.firma
The advanced electronic signature SAT issues. A certificate (.cer), a private key (.key) and its password that identify you in digital filings and count as your handwritten signature.
When tax rules require filing a document, it must be digital and carry its author’s advanced electronic signature (firma electrónica avanzada). SAT calls it the e.firma (formerly FIEL).
What it is, concretely
- A certificate (
.cer) linking the person to their signing data. - A private key (
.key) with its password.
Signed with a valid certificate, a digital document has the same effects and evidentiary value as one signed by hand.
How you get it and how long it lasts
You request it from SAT, which validates your identity and address; it requires appearing in person. Certificates are valid for at most four years from issue, and you can request a new one before it expires.
What you need it for
For filings that require it, such as requesting your CSD to invoice, and for SAT’s bulk CFDI download: with the password (CIEC) you cannot request XML in bulk.
Related terms
Posts about this term
- Buzón Tributario: fines from January 2027 and how to enable itFrom January 1, 2027, SAT can fine you $3,850 to $11,540 for not having the Buzón Tributario enabled. What it is, who must have it and how to activate it step by step.
- Tax changes for 2027: what actually changes for accountants and SMBsRESICO up to 5 million, Buzón Tributario fines, regularization and new limits on deductions. A clear summary of the 2027 Economic Package.
- How to handle 20 or more RFCs in an accounting firm without losing controlThe five tasks that take the most time at a firm with many clients and how to organize them: downloads, reviews, mailboxes, e.firmas and the team.
Not tax advice: review your case with your accountant.
Sources
Clauhub checks it in your invoices.
Download your CFDI with your e.firma and get 69-B, cancellation and REP alerts.
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