Implementing Electronic Card Payment Systems (Artech House Computer Security Series)

5.1 Certification mechanism and algorithm

In the EMV ¢ environment, a certifier is the organization that produces an EMV ¢ certificate using an asymmetric mechanism, consisting of a digital signature scheme providing message recovery, as stated in Annex A2.1 in Book 2 [1]. In Appendix D, Section D.3.2, of this book the reader can find a brief review of this mechanism. It is important to note that in Annex B.2 in Book 2 [1] the only cryptographic algorithm approved at the moment in the EMV 2000 specifications to implement an asymmetric mechanism is the RSA algorithm.

Then, without restraining the generality, someone can say that the certifier runs an RSA scheme, where the mapping of its parameters according to the EMV ¢ terminology is the following (see also Appendix F in this book):

• The modulus , denoted in the RSA context n , represents the certifier public key modulus data object in the EMV ¢ context.

• The public exponent, denoted in the RSA context e , represents the certifier public key exponent data object in the EMV ¢ context. Note that the certifier public key consists of the certifier public key modulus and the certifier public key exponent, which in the RSA context represents the public key ( n, e ). It is used by anyone that verifies the certificate.

• The secret exponent, denoted in the RSA context d , could be assimilated with a certifier secret key exponent data object, which is not explicitly defined in the EMV ¢ context. Note that the certifier private key consists of the certifier public key modulus and the certifier secret key exponent, which in the RSA context represents the private key ( n, d ). The certifier uses the certifier private key to generate the signature representing the certificate.