BES (Basic Electronic Signature) signature is the most basic signature type. There is no trusted time information that guarantees the date of signature creation.

The lifetime of the BES signature is up to the lifetime of the end entity certificate. The signature cannot be verified after the certificate has expired or the certificate has been revoked. For this reason, timestamping of the BES signature is extremely important. Time information in the BES signature can be added as a signing time attribute. However, there is no legal obligation or no certainty of the time added.

The cryptographic signature value in the BES signature is obtained by signing the cryptographic hash value of the Signed Attributes field. The “Message Digest” field where the hash value of the content to be signed is kept is also found under Signed Attributes.

The mandatory signed attributes for BES signature are as follows:

Content Type: It contains the type of the signed content.

Message Digest: It contains the hash value of the content to be signed.

Enhanced Security Services - Signing Certificate: It is an attribute that references the signer certificate and restricts the set of certificates to be used in signature validation. In addition, it must be added to eliminate possible security attacks from malevolent individuals such as changing the signer certificate.

Apart from these, a number of signed features can be added, which are not mandatory but will enrich the BES signature. The sample signed attributes are given in the following.

Signing Time: Indicates the time at which the signature was created in the manner declared by the signer.

Signer-location: The location information where the signature was created can be added to the signature.

Content-time-stamp: This is the time stamp which covers the content before it is signed.

The following table specifies the signature properties that must be included in the signature file for CAdES-BES signature format:

M: Must - It is mandatory to include the specified attribute. If the attribute is not included, the e-signature conformity assessment will result in negative.

O: Optional – It is optional to include the specified attribute. If the attribute is not included, the e-signature conformity assessment will not result in negative.

- : This means the attribute is not supposed to be included in the related signature type.

It is recommended not to use the optional attributes unless needed.

The time info received from the signer's computer or the related server does not assure the accuracy of the signing time because it is not signed by a trusted authority. For this reason, it is not recommended to use the signing time attribute as a legal evidence. If it is used, it must be adjusted so that it is left behind from the timestamp.

You can access CAdES-BES Detached Test Package from here.

You can access CAdES-BES Attached Test Package from here.

You can access test root certificates from here.

The following table provides the names and the properties of the signature files to be used in the procedures:

* One of the following methods must be selected when verifying the signed document if the signer certificate includes a monetary limit:

• “INVALID Signature” message must be displayed. The description of the error should be reported to the user.
• The monetary limit of the certificate is compared with the monetary limit of the signed document and if the monetary limit of the certificate is sufficient for the monetary value of the signed document, “VALID Signature” message must be displayed.
• In the case where the monetary limit of the certificate is not compared with the monetary limit of the signed document, the user should be warned that the signer certificate has a monetary limit and “VALID Signature” message must be displayed.