Mumbai University > Computer Engineering > Sem 6 > Mobile Communication & Computing

Marks: 5 Marks

Year: Dec 2016

Digital Certificate:

• An attachment to an electronic message used for security purposes. The most common use of a digital certificate is to verify that a user sending a message is who he or she claims to be, and to provide the receiver with the means to encode a reply.

• An individual wishing to send an encrypted message applies for a digital certificate from a Certificate Authority (CA).

  

  Figure:Digital Signature for a certificate

• A certificate contains information that identifies the certificate's owner (called the subject) as an entity on the network. A certificate also contains the owner's public key. Furthermore, a certificate identifies the CA (called the issuer) that issued the certificate.
• A CA uses its private key to digitally sign each certificate it issues. To create the digital signature, the CA generates a message digest from the certificate, encrypts the digest with its private key, and includes the digital signature as part of the certificate.
• Anyone can use the message digest function and the CA's public key to verify the certificate's integrity. If a certificate becomes corrupted or someone tampers with it, the message digest for the altered certificate does not match the digest in the CA's digital signature.
• The CA issues an encrypted digital certificate containing the applicant's public key and a variety of other identification information.
• The CA makes its own public key readily available through print publicity or perhaps on the Internet.
• The recipient of an encrypted message uses the CA's public key to decode the digital certificate attached to the message, verifies it as issued by the CA and then obtains the sender's public key and identification information held within the certificate. With this information, the recipient can send an encrypted reply.