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Digital Signature

Digital signature is used for the authentication of senders by applying public key cryptography in reverse. To make a digital signature a sender encrypts a message with her private key. In this case any receivers with her public key can read it, but the receiver can be sure that the sender is really the author of the message. A digital signature is usually attached to the sent message just like the handwritten signature.

Message Digest

To make the digital signature the base message needs to be normalized to a predetermined length of 160 bits, regardless of the length of the original message. This normalization process can be achieved by hashing the original message. This hashed message is called a message digest.

Certificates

A certificate usually implies an identifying certificate that is issued by a trusted third=party certificate authority (CA). A certificate includes records such as a serial number, name of owner, owner’s public keys (one for secret key exchange as receivers and one for digital signature as sender) an algorithm that uses these keys, certificate type (cardholder, merchant, or payment gateway), name of CA, and CA’s digital signature.

Certificate Authority

Certificate authority is a body, either public or private, that seeks to fill the need for trusted third-party services in EC. A CA accomplishes this by issuing digital certificates that attest to certain facts about the subject of the certificate.

In the context of credit cards, the cardholder certificate authority (CCA) issues the certificates to the cardholders, the merchant certificate authority (MCA) to merchants who operate e-stores, and the payment gateways certificate authority (PCA) to payment gateway service providers.
The CA should get their own certificate from a nationally designated CA, which is called a Geopolitical Certificate Authority (GCA).

Digital Envelope

Digital envelope is a process of encrypting a secret key with the receivers’ public key. The DES key encrypted in this manner is called a digital envelope. Because the DES key should be opened first to decrypt the message contents with the key.