Electronic signature e.firma — A must-have tool for every taxpayer in Mexico. Without a valid e.firma, it is almost impossible to fully conduct tax activities and use most of the digital services of the Tax Administration Service (SAT). The validity period of e.firma is limited and must be renewed in a timely manner.
SAT uses e.firma as its official digital taxpayer identification mechanism. e.firma — This is a digital signature that is legally equivalent to a handwritten signature. It confirms the identity of a person or company and makes it possible to sign electronic documents with full legal force.
The e.firma electronic signature consists of several elements:
- certificate.cer file
- private key.key
- password for the key
- SAT certificate
e.firma is used for:
- filing annual and monthly declarations,
- registration and change of tax regime,
- signing documentation for SAT,
- issuing electronic CFDI invoices and other electronic invoicing operations,
- opening of companies,
- working with notaries,
- access to some government digital services.
For entrepreneurs, having a valid e.firma is virtually mandatory.
Individuals without entrepreneurial activity sometimes live for years without e.firma, using only the SAT password. But for business, freelancing, contracts and most serious tax procedures, e.firma is necessary. Typically, e.firma is issued upon first application to SAT for registration in the RFC taxpayer register. However, foreign residents are issued an e.firma only when they declare their desire to conduct business and have a work permit.
Initial registration always involves a personal visit to the SAT office after making an appointment. At the same time, the retina of the eyes is scanned. The e.firma kit is recorded on a flash drive, which the taxpayer brings with him.
Standard validity period of e.firma — 4 years from the date of issue. It is important to know the exact end date, not just the year.
You can check your e.firma status online through the SAT portal. To do this, they usually use a certificate recovery service, which displays the issue date, expiration date, certificate status, and whether the signature is active.
In addition, validity can be checked through the .cer and .key files. If the certificate has expired, the SAT system will immediately report this when you try to sign documents with these files.
If the validity period expired less than a year ago, renewal can be completed online through the systemSAT ID. And it's very simple! Additionally, Certifica programs and the CertiSAT portal can be used to generate new .cer and .key files.
The procedure looks something like this:
- open the SAT ID portal,
- select the e.firma update option (renovación de e.firma),
- enter your RFC, phone and email,
- upload your ID card,
- confirm identity via video (show your face in close-up, slowly turn your head, read a random phrase or set of numbers from the screen, confirm consent to the procedure),
- sign an electronic application.
SAT then verifies the request and issues a new certificate. Typically, verification of an application through SAT ID takes from several hours to 3-5 business days. Once approved, SAT opens the way to download a new e.firma certificate.
However, e.firma online renewal is not always available. You need to take the SAT in person if:
- e.firma expired more than a year ago,
- lost .key file,
- lost password,
- there are no old certificates,
- the signature has been revoked or blocked,
- online identification failed.
In such cases, when visiting the SAT office, a new e.firma is actually issued with a re-verification of identity.
Formally, you can renew your signature even one day before its expiration date. But it is better to check the validity period at least once a year and update e.firma at least a few weeks before the certificate expires.