X.509 Certificate Encoding and Extensions

An X.509 certificate is a digital certificate which uses international X.509 public key infrastructure (PKI) standard to verify a public key. X.509 certificate is defined using ASN.1
Understanding different encodings:

 1. PEM:

•   ASCII(Base64) encoded data
•   File extension is .cer

 2. DER:

•   Binary form of ASCII PEM format certificate
•   File extension can be .cer or .der

3. P7b/PKCS#7 :

•  This are base64 encoded . Contains “—–BEGIN PKCS—–” & “—–END PKCS7—–” statements.
•  They have extensions .p7b, .p7c

4. PFX/PKCS#12:

•   They are Binary format files  storing the Server certificate.
•   They have extensions .pfx, .p12

 

Understanding different files/extensions:

• .Pem -   Includes private and public key in ASCII PEM format
• .p12 - An archive file format for storing many cryptography objects as a single file.
• .key- Contains private key.  The KEY extension is used both for public and private PKCS#8 keys. The keys may be encoded as binary DER or as ASCII PEM.
•  .csr - Stands for certificate signing request. A certificate authority will use a CSR to create your SSL certificate
•  .cer & .crt -  This can be interchangeable format .cer is Microsoft extension
•  .config - Contains the configuration for creating certificate