Certificate File Format Summary

PKI Certificate Tutorials - Herong's Tutorial Examples

∟Certificate File Format Summary

This section provides a summary of 5 commonly used file formats of PKI certificates: DER, PEM, PKCS7 Binary, PKCS7 Text, and PKCS12.

As a summary, here is my understanding of PKI certificate data structure and its commonly used file formats.

A PKI certificate uses ASN.1 data structure to record its data elements.

A PKI certificate can be stored in a file in 5 commonly used formats.

1. DER Format - The PKI certificate is encoded using the DER (Distinguished Encoding Rules) standard into a binary file. Commonly used file extensions are: .der, .cer, .crt.

2. PEM Format - The PKI certificate is encoded using the DER (Distinguished Encoding Rules) standard, encoded again using the Base64 standard, and wrapped in PEM format. Commonly used file extensions are: .pem, .cer, .crt.

Multiple certificates can be concatenated in a single PEM format.

3. PKCS7 Binary Format - The PKI certificate is wrapped as an object using the PKCS7 (Public-Key Cryptography Standard #7) standard, and encoded using the DER standard. Commonly used file extensions are: .p7b, .p7c, .p7r.

Multiple certificates can be wrapped in a single PKCS7 file.

4. PKCS7 Text Format - The PKI certificate is wrapped as an object using the PKCS7 (Public-Key Cryptography Standard #7) standard, encoded using the DER standard, encoded again using the Base64 standard, and wrapped in PEM format. Commonly used file extensions are: .p7b, .p7c, .p7r.

Multiple certificates can be wrapped in a single PKCS7 file.

5. PKCS12 Format - The PKI certificate is wrapped as an object using the PKCS12 (Public-Key Cryptography Standard #12) standard, and encoded using the DER standard. Commonly used file extensions are: .p12, .pfx, .jks.