What is DER? What Opens a DER? File Format List from WhatIs.com

File Extension

DER File Format

Certificate file

The DER file extension is primarily associated with a DER- (Distinguished Encoding Rules) encoded X509 digital certificate file. 

A digital certificate is issued by a certification authority (CA) and contains a certificate holder's name, a serial number, expiration dates, a copy of their public key (used for encrypting messages and digital signatures), and the digital signature of the certificate-issuing authority to verify that the certificate is valid.

Learn more:

SearchSecurity.com explains the public key infrastructure (PKI) and digital certificates.

Randall Gamby discusses digital signatures and digital certificates.

Also from SearchSecurity.com, here's a collection of news and learning resources about digital certificates.

See questions and answers about digital certificates

This was last updated in September 2010
Editorial Director Margaret Rouse

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