ContentInfo

ContentInfo is the outer CMS envelope — every CMS structure is wrapped in a ContentInfo SEQUENCE. It is the standard entry point for parsing any CMS payload.

Class

class ContentInfo:
    @staticmethod
    def from_der(data: bytes) -> ContentInfo: ...
    # Parse a DER- or BER-encoded ContentInfo SEQUENCE.

    def to_der(self) -> bytes: ...

    content_type_oid: ObjectIdentifier
    # e.g. ID_SIGNED_DATA, ID_ENVELOPED_DATA, ID_ENCRYPTED_DATA, …

    content: bytes
    # Raw bytes of the content field (including the [0] EXPLICIT tag for most types).

Usage

from synta.cms import ContentInfo, ID_SIGNED_DATA, ID_ENVELOPED_DATA, ID_ENCRYPTED_DATA

data = open("message.p7m", "rb").read()
ci = ContentInfo.from_der(data)

print(ci.content_type_oid)  # e.g. ObjectIdentifier("1.2.840.113549.1.7.2")

if ci.content_type_oid == ID_SIGNED_DATA:
    from synta.cms import SignedData
    sd = SignedData.from_der(ci.content)
    print(f"Signers: {len(sd.signer_infos)}")

elif ci.content_type_oid == ID_ENVELOPED_DATA:
    from synta.cms import EnvelopedData
    ed = EnvelopedData.from_der(ci.content)
    # decrypt with ed.decrypt(private_key)

elif ci.content_type_oid == ID_ENCRYPTED_DATA:
    from synta.cms import EncryptedData
    enc = EncryptedData.from_der(ci.content)
    # decrypt with enc.decrypt(key)

See also the CMS Overview for a summary of all content types.