Qualified signatures with CMD

Mobile Digital Key is the Portuguese State’s electronic identity service. In AssinaJá it is the only way to produce a QES — a signature legally equivalent to signing by hand across the European Union.

Why CMD is qualified

What makes a signature qualified is not the platform that collects it, but who issues the certificate and where the private key lives.


Issuer	AMA — Agência para a Modernização Administrativa, a QTSP on the Portuguese EU Trust List
Private key	In AMA’s HSM — never on your phone, never in AssinaJá
eIDAS level	QES
Identity verification	High

AssinaJá is not a qualified trust service provider. The qualified character comes exclusively from AMA — AssinaJá prepares the document, hands AMA the cryptographic digest, and assembles the result.

Before you can sign

Your Chave Móvel Digital must have Digital Signature activated. Having CMD for authentication is not enough — signing is a separate feature, activated at autenticacao.gov.pt.

If it is not active, AMA returns no certificate and AssinaJá shows:

AMA did not return any signing certificate for this phone number. Check that the number is correct and that your Chave Móvel Digital has the signing feature activated at https://www.autenticacao.gov.pt.

Signing with CMD, step by step

Complete your visual signatures first. If the document also asks you for initials or a simple signature, fill those in before. CMD seals the document, and after it only further CMD signatures can be added.
Enter the phone number linked to your CMD and your signing PIN (4 to 8 digits). Note it is the signing PIN, distinct from the authentication PIN.
Receive the security code. Six digits, arriving either by SMS or from the authenticator in the Chave Móvel Digital app:

To confirm the signature, enter within the next 2 minutes the security code shown in the Chave Móvel Digital app authenticator or the code sent to your phone.
Enter it within 2 minutes. After that: “The time to enter the security code has expired. Please cancel and try signing again.”

The screen warns you before proceeding — WARNING: You are about to perform a valid electronic signature with the Digital Mobile Key. — and it means it: from that step the signature is irreversible.

If the code does not arrive, Did not get the code? Restart request is offered. Asking again too quickly is refused; there is a 20-second wait between requests.

CMD and CMD with Professional Attributes

This is the distinction that confuses most, and it states simply:

CMD proves who signed.
CMD with Professional Attributes (SCAP) proves in what capacity they signed — and that capacity is attested cryptographically by the certifying body itself, not by the signer and not by AssinaJá.

SCAP is the State-run Sistema de Certificação de Atributos Profissionais. A lawyer signing with SCAP is not merely signing as a citizen: the document gains an additional signature from the professional body, confirming that on that date they held that capacity.

What changes when signing

	CMD	CMD with Attributes
Prior authentication	—	OAuth at autenticacao.gov.pt
Choosing attributes	—	At least one, from those available
Phone + PIN	Yes	Yes
Security code	Yes	Yes
Signatures on the final PDF	Platform seal + your QES	Platform seal + your QES + one per certifying body

In the attributes step each body appears with its attributes as checkboxes. You may pick several, including across different bodies, but at least one is required — “Select at least one attribute”.

What becomes visible on the document

A signature with attributes adds three lines to the stamp, beyond name and date:

Line	Content
Certificado com:	`SCAP`
Certificado Por:	The certifying bodies
Atributos Certificados:	The chosen attributes, per body

The same information appears in the Completion Report and is recorded as evidence attached to the signer.

Rules to know

Rule	What it means
One qualified zone per signer and document	“You can only have one signature of this kind for each signer/document combination.”
CMD or CMD with Attributes, never both	A signer can hold visual signatures and one qualified method, but not both qualified methods
Phone number required	“If you indicate signers with Signature with Digital Certificate, the phone number is required.”
Already-signed documents	A PDF that already carries digital signatures accepts only CMD or CMD with Attributes, so the existing ones stay valid
“Sign now” does not support CMD	The owner’s immediate signing does not go through AMA; the document has to be sent for signature
Digital certification becomes redundant	“A certificação digital não é necessária quando o documento vai ser assinado por signatários com CMD ou CMD SCAP…”

Both methods consume the same CMD quota from the subscription. When it runs out: “Digital Mobile Key (CMD) document limit reached”.

If something goes wrong

Message	Meaning
The Chave Móvel Digital (AMA) signature failed	“Isto é uma falha do serviço da AMA…, não do documento. Pode tentar novamente.”
O serviço da Chave Móvel Digital não se encontra disponível.	AMA-side outage
The security code is incorrect.	Wrong code
The security code has expired.	The 2 minutes elapsed
The pin you provided is incorrect.	Wrong signing PIN
Invalid mobile number.	Phone number format
A sessão de assinatura expirou.	Start the process again
Sem resposta do servidor de assinatura.	Check the connection and retry

The most useful distinction in that table: the first two are AMA’s, not AssinaJá’s and not the document’s. Retrying later usually resolves them.

Signature longevity

A CMD signature sits at the PAdES-BASELINE-T profile: a qualified signature plus a qualified timestamp. It is fully valid.

What is not embedded is the certificate’s revocation information, because the Citizen Card certificate does not publish a suitable access point. In practice that does not affect the signature’s validity today, but it does affect how easily it can be verified many years from now, once the certificate has expired.

That is why the advice to validate and archive is not a formality: keep the signed PDF and the Completion Report, together.