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Signature Creation Smart Cards
E-Sign K: Application Interface for Smart Cards as Secure Signature Creation Devices
by Gisela Meister – G+D, München, E-Sign K Chair
This paper describes the new European standard for Secure Signature Creation Devices (SSCDs) focussed on smart cards. This standard is in accordance to requirements of the “EU Directive 1999/93/EC of the European Parliament and the council of 13 December 1999 on a Community framework for electronic signatures”.
Electronic signature applications require standardisation activities according to several aspects:
- Issue 1: The quality of electronic signatures should be acknowledged by the user:
– Verifier as well as signer have to rely on their trustworthiness.
This issue is especially of legislative importance and is expressed in the European Directive for electronic signatures [EU_DIRECTIVE]. The further issues are important from the technical point of view:
- Issue 2: The format for electronic signatures and their certificates should be interoperable:
– Signatures are to be verified in different application and environment context including device type and software module or version respectively, i.e.: The signature will be verified in an environment context not known to the signer
- Issue3: The device interface (physical, logical and application interface) should be interoperable at least for the same device type:
– The signature may be created at a different location by the user: public under provider control (e.g. airport, hotel) or under user control in an environment, mobile or location dependent, set by
Administration,
Physician,
User’s office (Intranet environment) respectively or
At home connected with the Internet or offline.
Figure 1. Public Key schemes (asymmetric schemes) for qualified electronic signatures are used together with tokens as smart cards to store the private key (Secret Key), to calculate the signature inside the token and to deliver the Public Key inside certificates indicating additionally the signer´s name and the algorithm used, e.g. RSA, DSA , elliptic curves respectively.
This paper describes the European standardisation activities and solutions for smart cards as a special type of Secure Signature Creation Device (SSCD).
Thereby the focus, solely on European activities, is not as restrictive as it seems at first view because national non-European projects are likely to take this work into account.
Smart cards are selected as representatives for SSCDs because of the following reasons:
Smart cards are computers on their own, being the size of a business card or even smaller in case of the SIM cards for mobile phones.
Smart cards
- are able to fulfil quality assurance as required by Issue1.
– There are already successful evaluations on the market.
– Smart cards can be used as representatives for SSCD’s checking the consistency of requirements from existing quality standards (see [ESIGNF], [ESIGNG1]).
- can serve as a storage for data, can interpret input data forma and can create the appropriate data format for output according to Issue2.
- are flexible devices which can easily be transported by the user as required by Issue3.
- already use international and national standards on physical, logical and application layers respectively, which can be built as a base for the elaboration of a European standard (see the ISO/IEC 7816 series, esp. [ISO7816-4], [ISO7816-8], ISO7816-15] according to Issue3.
ESIGN Standardisation and their roots.
The EU standardisation activities did not focus on electronic signatures on smart cards at first, but described requirements for
- “advanced electronic signatures”1 – on product neutral token called “Secure Signature Creation Devices” (SSCDs)2
These electronic signatures, if used together with qualified certificates are in shortly called “qualified signatures”.
Fig. 2. Structure of a SSCD according to [ESIGNF]
In the CEN/ISSS Workshop on Electronic Signatures (WS/E-Sign), an initiative founded by European standardisation bodies CEN, CENELEC and ETSI, recent standardisation work for has been accomplished (see Fig. 2).
Fig. 3. Overview of workgroups relevant for smart cards
The E-Sign group G1 defined requirements for the Environment of the SSCD and the interfaces between application on the PC side and SSCD.
The E-Sign Group F mapped these requirements into Protection Profiles following Common Criteria EAL 4 res. ITSEC EAL 4+ and to be used in a product specific evaluation process further on.
The European Algorithm Workgroup, initialised by the EESSI steering committee, but working independently, has recently defined algorithm suits (algorithms and parameters including hash values and padding formats) which are to be used in connection with qualified electronic signatures.
All documents are an important input for the development of smart card applications following the requirements of the EU Directive and are delivered to the respective Article 9 committee (see figure 2).
“Application Interface for Smart Cards used as Secure Signature Creation Devices” by E-SIGN K
- The E-SIGN K group was established to define a standard for smart cards following the issues 1 to 3, presented in the introduction. This should be accomplished in combining existing standards for smart cards with
- requirements originating from the already achieved work from the E-SIGN Workshop and from
- already existing national or application specific specifications about electronic signatures for smart cards.
The scope therefore claims the document to cover general items as
- mapping of general requirements to asymmetric techniques to be able to specify the electronic signature format (Issue2)
- command and responses seen at the interface to the Smart Card according to ISO/IEC 7816 standards, mainly part 4 and part 8 (Issue 3)
- cryptographic information application according to CD 7816-15, the PKCS#15-derivate for smart cards (Issue 3)
the usage of signature schemes according to the European algorithm catalogue for:
- electronic signatures (Issue1 and 2)
- device authentication and signature verification requirements (Issue 3)
- User verification management, knowledge based or based on biometrics (Issue 3)
- storage and retrieval (loading) of certificates (roots) of different kinds and levels (Issue 2)
- application selection (Issue 3)
- card management related aspects (Issue 3).
The underlying smart card platform can be open platform orientated as used by Java or MULTOS Cards accompanied by an ISO/EC 7816 run time environment as already implemented for GSM cards with WAP facilities or can possess an operating system which solely work under ISO/IEC 7816 conditions as for instance the German Geldkarte with SECCOS or the Finnish ID card.
Signature Application Architecture
According to the actual draft version, the signature application is designed following requirements due to [ESIGNG1]. Thereby it is oriented on the well-known international standard series for contact oriented cards, the ISO/IEC 7816 series for smart cards. Especially the cryptographic command set is based on ISO/IEC 7816-8 , res. CD 7816-4.
The G1 specification [ESIGNG1] distinguishes two different types of environments – a private or office environment which is controlled by the signer and a public environment controlled by a service provider (see. Fig. 4). The communication to and from the SSCD is performed by a trusted path required by the Protection Profile designed by [ESIGNF] for the SSCD.
In case of a public environment the protection of the interaction sequences can be performed by means of a trusted channel between the smart card and an authentication module inside the Secure Signature Creation Application (SSCA), the respective user environment for electronic signature creation.
Thereby a trusted channel is especially a trusted path with the additional feature that both sides have established a protected communication by cryptographic means, the strength of function valid for a successful evaluation.
In the E-SIGN K draft special techniques are mentioned to achieve such a trusted channel by defining suitable authentication protocols on asymmetric bases.
Fig. 4. Trusted path between Signature Creation Application (PC environment) and SSCD (Smart card) according to [ESIGNGF].
For the purpose of interoperability, mutual device authentication protocols according to international standards ( ISO/IEC SC 27) are specified for different mechanisms as RSA, DSA and Elliptic Curves. Hereby the algorithm, implemented on the card, is indicated by a corresponding certificate and is sent to the terminal for the purpose that this algorithm is to be used by the terminal as well. This authentication certificate is similar to the certificate used for the signing process (see figure 1), only now it is linked to the card and not to the signer.
During the authentication a session key will be established from both sides, only to be used in the following session. This can be achieved by secure messaging as defined in ISO/IEC 7816-4.
For private use, e.g. for mobile telecommunication, no authentication method should be needed, because a trusted path is already achieved by organisational means, if the mobile phone is under sole control of its owner.
Fig. 5. Interaction sequences between Signature Creation Application (SCA) and smart card as SSCD according to [ESIGNGK ],ESIGNG1]
Outlook
Electronic signatures can only be accepted if availability and quality is guaranteed. This can be accomplished, if quality and interoperability standards are used in the creation and verification process. Smart cards are a suitable tool to achieve both.
Participation from card manufacturers, issuers, appliers and security experts on E-SIGN K would help to establish a harmonised standard in Europe, which is likely to be accepted internationally. The next meeting of E-SIGN K will be at the end of January in Barcelona. The document is expected to be finished before the end of the year.
Biography
[DIN V66291-1]
DIN V66291-1: 1999, Chipcards with digital signature application/function according to SigG and SigV, Part 1: Application Interface
[DIN V66291-4]
DIN V66291-4: 2000, Chipcards with digital signature application/function according to SigG and SigV, Part 4: Basic Security Services
[EU_DIRECTIVE]
EU Directive 1999/93/EC of the European Parliament and the council of 13 December 1999 on a Community framework for electronic signatures
[ESIGNF]
Secure Signature Creation Devices, CEN/ISSS WS/E-Sign Project Team on Area F, CEN Agreement Group F, , CEN//ISSS WS/E-Sign Workshop ISSS WS/E-Sign N 104 Graz/2000-1 1-15,
[ESIGNG1]
Security Requirements for Signature Creation Applications, CEN /ISSS WS/E-Sign Workshop Agreement Group G1, Draft Version 3.5, February, 2001
[ESIGNK]
Application Interface for SmartCards used as Secure Signature Creation Devices, CEN Working Draft, Vers. 0.6, January 2002
[EU-ALGO]
Algorithms and Parameters for Secure Electronic Signatures European Algorithm catalogue for qualified electronic signatures, V.2.1 Oct 19th 2001
[ISO7816-4]
ISO/IEC 7816-4: ISO/IEC 7816-4: 1995, Information technology – Identification cards – Integrated circuit(s) cards with contacts , Part 4: Interindustry commands for interchange, IS 1995, CD January 2002
[ISO7816-8]
ISO/IEC 7816-8: IS 1998, Information technology – Identification cards – Integrated circuit(s) cards with contacts – Part 8: Security related interindustry commands [ISO/IEC 7816-9]
1. An advanced electronic signature is a high quality electronic signature:
According to the EU Directive an advanced electronic signature means an electronic signature which meets the following requirements:
(a) it is uniquely linked to the signatory;
(b) it is capable of identifying the signatory;
(c) it is created using means that the signatory can maintain under his sole control; and
(d) it is linked to the data to which it relates in such a manner that any subsequent change of the data is detectable.
Following Annex III, 1: Secure signature-creation devices must, by appropriate technical and procedural means, ensure at the least that:
(a-1) the signature-creation-data used for signature generation can practically occur only once,
(a-2) secrecy of the signature-creation-data is reasonably assured;
(b-1) the signature-creation-data used for signature generation cannot, with reasonable assurance, be derived
(b-2) the signature is protected against forgery using currently available technology;
(c) the signature-creation-data used for signature generation can be reliably protected by the legitimate signatory against the use of others.
2. According to the EU Directive [EU_DIRECTIVE] Secure Signature Creation Devices (SSCD) are able to store private signature keys of a card holder without delivering the key to the outside world. Therefore the calculation of the signature algorithm as well as its storage is performed inside the SSCD.
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