Guidance on
Achieving Qualified
Remote eSigning for eIDAS Compliance

INTRODUCING CRYPTOMATHIC SIGNER

Signer is a secure digital signature server solution that offers eIDAS certified remote eSigning, giving users the freedom to digitally sign documents at any time, from anywhere in the world, on any device. Cryptomathic Signer is a strong enabler of large organizations’ digitalization strategies. Signer offers enhanced security, ease of deployment and user mobility with remote signature generation. It is a zero-footprint signing technology that can offer an appropriate security assurance level while being compatible with all types of devices. Cryptomathic Signer can be used to generate Advanced or Qualified Electronic Signatures (AdES or QES).

Cryptomathic Signer allows for easy integration with web application servers and can leverage existing 2FA deployments.

Deploying Signer - Functional Overview

Signer offers different integration options with existing applications, systems, processes and user-workflows - based on your requirements. The illustration on the right is a general overview of the entities in a remote signing service.

Signer: End-User Experience

Users typically start by logging into a web application that controls the business workflow. When a document needs to be signed, the user is invited to click on a “View and Sign” button. The document is automatically prepared and securely rendered into the browsing session using Cryptomathic WYSIWYS technology which acts as “trusted viewer” for user confidence and non-repudiation. WYSIWYS ensures that only the authentic document can be signed by the user.

The user can view the document again before committing to it. To ensure only the correct user can generate their signature, the user is required to use strong authentication to invoke and authorize the signature operation.

Once the signature is generated, it is then embedded into the PDF or XML document in a standard format so that the user or any relying party may validate the signature afterwards.

Behind The Scenes

To commit to a document or a transaction, the user routes a signing request to Signer, authenticates him/herself (using strong authentication) to retain remote control over their signing key. The signing key is stored centrally in the secure, tamper resistant/ evident environment. Signer then generates the signature value and returns it to the client for secure embedding into the document or transaction using the appropriate signature profile. Cryptomathic Signer offers a direct path from the browser into the hardware security module (HSM) holding the user´s key using an advanced security protocol.

Why Signer?

Signer uniquely offers the combination of:

• ● Excellent user-experience: on desktop, tablet & mobile devices
• ● Compliance with European standards for issuing advanced and qualified electronic signatures
• ● Ability to reuse existing 2-factor authentication methods
• ● Full audit-trail of what was signed, when and by whom supports strong non-repudiation
• ● Protection against tampering with What You See Is What You Sign (WYSIWYS) technology
• ● Reduced operational costs compared to paper based and other e-signature solutions
• ● Support for different business models: can be provided as a complete solution on premise, as a hybrid managed service or in a pure service mode.

Commercial Models

Different customers will vary by size, technical capacity and have their own preferred business model. Signer’s secure and adaptable architecture makes it ideal for most applications requiring remote signing. Signer can be deployed in different arrangements to suit the desired business model. It also offers flexibility to organizations that wish to provide ‘signing services’ as a commercial offering.

Cryptomathic Signer can be deployed in three main commercial models:

1. A) On-Premise: Where the entire solution is installed on premise. An organization, such as a trust service provider (TSP), wishing to offer a signing service to its customers, acquires the certified QSCD and internally hosts all the supporting infrastructure.
2. B) Hybrid Signing Service): Where the organization, such as a bank, offering signatures to their end-users, integrates the modules within their applications, while the TSP elements are consumed as a service.
3. C) Fully Managed TSP: Whereby the customer receives a full service. Signer is offered as a fully managed service by a TSP for delivering a QES service to the market.

The different models offer flexibility in where liability resides and also address different appetites and abilities to host services as well as time to market (see overleaf).

Alternative Solutions

When developing a QES service, there are core functions which must always be considered:

• Identifying your customer
• Providing qualified certificates
• Providing a QSCD
• Integrating the signature process in the business workflow
• Delivering a user-friendly signing experience.

A signature service cannot be regarded as just another server. One needs to take into account the legal and procedural obligations around client identification. Additionally, there are policy enforcements and necessary practice statements that must be put in place for issuing qualified certificates.

Buying a best-of-breed remote signing solution is not the only route available to provide QES services. There are some potential attractions in considering ‘making’ a solution from components using internal or external development resource as well as the “traditional” personal PKI smart card approach.

Nevertheless, there are some risks or limitations with these approaches, including:

High certification costs:

When wanting a solution to comply to external standards (e.g. eIDAS) there are some large hurdles to overcome to gain certification, such as the costly Common Criteria certified QSCD signature devices. Certification typically takes upwards of 12 months and can cost 100s of thousands of €/$/£.

Security design expertise:

to engineer a solution that protects against both obvious and subtle attacks and subversions requires expert security architects and use of specialist devices such as HSMS (Hardware Security Modules). Patented technology: Many e-signature technologies are patented by various vendors. Developing a solution in-house may inadvertently lead to patent infringement.

High deployment cost:

A distributed system where users hold their signing key in a personal PKI device/smart card has several limitations, such as device compatibility, user mobility and high management overheads.

For customers who wish to deploy a cost-effective solution with predictable timescales, acquiring a remote signing solution such as Cryptomathic Signer will have less risk, a quicker time-to-market and will allow a focus on their core business strengths. It is therefore advisory to team up with a skilled partner and outsource parts or all of these activities to ensure that the deployment and the conformity assessment are successfully passed.

SECURITY AND COMPLIANCE

Cryptomathic Signer security design is, together with end-user convenience, of the utmost importance. The solution is designed to deliver Advanced and Qualified electronic signatures, as per the eIDAS and ZertES regulations.

Security and assurance The security design has various layers, including:

• A strong security kernel that enables, by means of firmware extensions, all the security sensitive operations inside the tamper evident environment of the Common Criteria EAL 4+ certified HSM
• The signing protocol that allows the data intended for signing to be sent over a secure communication channel so that all communication can be encrypted and integrity protected.
• Administration is privilege-based and all logs are stored in a high capacity integrity-protected database.

Compliance

The EU Commission together with the ETSI and CEN normalization committee has set standards around remote server signing and offers a clear legal framework for the roll-out of this technology.

Customers implementing the Signer technology need to undergo an audit performed by a security assessor recognized by a supervision body if they want the signature services to be certified as delivering Qualified Electronic Signatures. eIDAS is the EU regulation that enforces the following standards.

Relevant Standards

For an eIDAS compliant implementation allowing for the issuance of Qualified Electronic Signatures recognized across the EU member states, the following standards need to be observed:

CEN 419 241 - Security Requirements for Trustworthy Systems Supporting Server Signing, including:

• Existing CEN TS 419 241:2014
• New version 419 241-1
• Protection Profile for the QSCD 419 241-2
• Protection Profile for the HSM doing the signature operation (419 221-5 mentioned in the above standard).

ETSI EN 319 411-2:2015 for issuance of qualified certificates, including:

• CEN/TS 419 261:2015 Security requirements for trustworthy systems managing certificates and time-stamps.

Signature profiles must follow the PAdES (PDF signing), XAdES (XML transaction signing) and CAdES (CMS signing) family.

Other National Regulations

Cryptomathic also supports other signature laws beyond the European Union. In Switzerland, the ZertES regulation offers mutual recognition of TSP / Qualified Certificates using multilateral contracts.

Around the world signature laws generally follow two approaches:

1. A Tiered model like eIDAS where assurance models are verified by a conformity assessor. Legal value is clear and guaranteed and typically offered at different levels, e.g. AdES and QES.
2. An Open model where everything has legal effect but admissibility can always be questioned. The US and aligned countries follow this model.

Other counties that support the eIDAS-like tiered model include Hong Kong, Singapore and Japan.

CERTIFICATION

In order to provide AdES or QES within the EU, a business or TSP must go through a certification process, which is described in the following section.

The figure below illustrates the general workflow around service certification.

The European Commission is the entity that has defined the pan-European legal framework (eIDAS regulation and implementing acts) for the provisioning of (qualified) trust services including Qualified Electronic Signatures and for publishing the EU Trust List.

The European Commission has also commissioned standardization bodies ETSI and CEN to publish technical standards for amongst other issuance of qualified electronic certificates and electronic signatures.

The Supervisory Body is the national entity in charge of granting the qualified status to a Trust Service Provider (TSP). It relies on conformity assessment reports to verify the conformity of a TSP. It shall notify the European Commission on which TSPs operates in the member state. It has a regulation function.

The Conformity Assessment Body is the legal entity that performs a conformity assessment of the TSP against eIDAS regulation and relevant standards. It submits a conformity assessment report.

The Trust Services Provider is the legal entity that provides (qualified) trust services to individual and/or businesses. It is legally liable for the services provisioned.

The EU Trust List contains for each member state a list of trust service providers, what services they offer and what level it is recognized (qualified or advanced).

Certificates and CA domain

In the EU, an accredited certificate service provider (CSP) must comply with eIDAS and, depending on which services are offered, the CSP must meet specific technical standards, including:

• ETSI EN 319 411-2, for issuing qualified signature certificate
• ETSI EN 319 421, for issuing timestamp token
• ETSI 102042 NCP+, for issuing authentication certificate.

eIDAS qualification requires recurring audits (every 2 years) by an accredited evaluation body, the evaluation is a means to prove the trustworthiness of the CA and other IT systems.

An eIDAS security audit is based on a review of the existing documents and an inspection of the implemented mechanisms and security controls; therefore, the CA trust center should have up-to-date, proper and adequate documentation.

An essential part of the conformity assessment is to ensure that the procedures and practice statement set forth in the Certificate Policy / Certificate Practice Statement (CP/CPS) are effectively enforced.

SIGNATURE GENERATION SERVICE PROVIDER DOMAIN (SGSP)

eIDAS requires that qualified electronic signatures are created by qualified electronic signature creation devices (QSCDs).

Cryptomathic Signer – an eIDAS QSCD

Since the regulation includes requirements for QSCD, the conformity of the QCDSs shall be verified through certification. CEN TC224 WG17, as appointed by the European Commission, has created standards targeted for certification of products like Cryptomathic Signer. From CEN EN 419 241-1 the following architecture containing two parts can be derived:

1) Unprotected local environment - The local environment with all components running on the client side (user, device, and browser). This includes, in particular, the browser used to render the data to be signed as well as the Signer’s Interaction Component (SIC) for communication with the remote TSP. The SIC corresponds to the JavaScript based WYSIWYS client. The environment is unprotected as it is not under the TSP’s control.

2) Remote TSP protected environment - The remote environment corresponds to the back end of the TSP containing a Server Signing Application (SSA), like Cryptomathic Signer, which uses a HSM. The HSM contains two modules, a Signature Activation Module (SAM), which authorizes the signature operation, and a Cryptographic Module, which generate and use signing keys. The HSM must conform with EN 419 221-5 (Published December 2016) and the SAM with EN 419 241-2 to be a QSCD.

The SAD is the Signature Activation Data, which cryptographically binds together information about:

• Who is the signatory
• What is to be signed
• Which signature key is to be used for signing.

The SAD is transmitted from the SIC to the SAM, where it is verified and used to activate the signature key.

The CAB Audit

The Conformity Assessment Body (CAB) is the legal entity that performs a conformity assessment of the TSP against eIDAS regulations and relevant standards and submits a conformity assessment report to the Supervisory Body (SB).

The SB reserves the rights of additional audit or conformity assessment at any time to confirm that requirements are fulfilled. European Accreditation (EA) defines common rules for all national accreditation bodies to implement. The common rules are based on ETSI and ISO standards.

eIDAS certified CABs perform two audits to verify compliance against the eIDAS regulation:

• Pre-assessment: This includes documentation assessment (i.e. technical, functional, and organizational security measures) and their appropriateness for fulfilment of eIDAS requirements. This also includes identification of applicants (qualified, experienced and reliable staff, sufficient financial resources, liability insurance, communication with supervisory body).
• On-site audit: This includes verification of implementation of security measures, processes, network, systems. The technical testing includes penetration testing.

A Conformity Assessment report detailing the findings of the audit is then submitted to the Supervisory Body, which ultimately decides if the TSP is entitled to receive the qualified level of certification and be referenced in the EU Trust List.