This library provides data structures and functions to represent, read, and write objects defined by PKCS #7 (RFC2315) and Cryptographic Message Syntax (RFC2630).

PKCS #7 and CMS are based on ASN.1. This library uses the Data.ASN1.Types.ASN1Object class of the asn1-types library to read and write objects, meaning you will the fromASN1 and toASN1 to convert between ASN1 and PKCS #7 objects. To read and write ASN1 sequences, use the functionality of Data.ASN1.Encoding in the asn1-encoding library.

import Data.ByteString         (ByteString)
import Data.ASN1.Types         (fromASN1)
import Data.ASN1.Encoding      (decodeASN1', DER)
import Data.Pkcs7.Types        (contentContent)
import Data.Pkcs7.DigestedData (digestedContent)

extract :: ByteString -> ByteString
extract input = data
    where (Right asn1) = decodeASN1' DER input
          (object, _) = fromASN1 asn1
          (Data data) = contentContent $ digestedContent object

Some data structures, such as ContentInfo or Attribute, can be parameterized with a custom data type. You can use the Any type leave the field unrestricted and retain the original ASN1 encoding. Other common parameter types are Data for encapsulated binary data and None if the specification requires the field to not contain a value.