What Is PKCS7 File Format

PKI Certificate Tutorials - Herong's Tutorial Examples

∟What Is PKCS7 File Format

This section describes the PKCS7 File Format, which can be used to store multiple signed and/or encrypted data items, including certificates and CRL (Certificate Revocation List) in a single file.

What Is PKCS7 File Format? PKCS7 file format follows the PKCS #7 (Public-Key Cryptography Standard #7) standard. It can be used to store multiple signed and/or encrypted data items, including certificates and CRL (Certificate Revocation List) in a single file.

PKCS7 file format is specified in RFC 2315 "PKCS #7: Cryptographic Message Syntax Version 1.5" at datatracker.ietf.org/doc/html/rfc2315.

A PKCS7 file is written in ASN.1 (Abstract Syntax Notation One) language. Its top level structure is shown in the example below:

d=0  hl=4 l=1344 cons: SEQUENCE          
  d=1  hl=2 l=   9 prim: OBJECT            :pkcs7-signedData
  d=1  hl=4 l=1329 cons: cont [ 0 ]        
    d=2  hl=4 l=1325 cons: SEQUENCE          
      d=3  hl=2 l=   1 prim: INTEGER           :01
      d=3  hl=2 l=   0 cons: SET               
      d=3  hl=2 l=  11 cons: SEQUENCE          
        d=4  hl=2 l=   9 prim: OBJECT            :pkcs7-data
      d=3  hl=4 l=1299 cons: cont [ 0 ]        
        d=4  hl=4 l= 367 cons: SEQUENCE          
          ... First certificate encoded here
     
        d=4  hl=4 l= 413 cons: SEQUENCE    
          ... Second certificate encoded here

        d=4  hl=4 l= 507 cons: SEQUENCE
          ... Third certificate encoded here

        ...

      d=3  hl=2 l=   0 cons: cont [ 1 ]        
      d=3  hl=2 l=   0 cons: SET