synta 0.2.2

ASN.1 parser, decoder, and encoder library with DER/BER support and C FFI
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# DigestedData and AuthenticatedData


## DigestedData

`DigestedData` implements RFC 5652 §7 — hash-protected content.

```python
class DigestedData:
    @staticmethod
    def from_der(data: bytes) -> DigestedData: ...
    def to_der(self) -> bytes: ...

    version: int
    digest_algorithm_oid: ObjectIdentifier
    digest_algorithm_params: bytes | None
    encap_content_type: ObjectIdentifier
    encap_content: bytes | None
    digest: bytes
```

### Usage

```python
from synta.cms import DigestedData

dd = DigestedData.from_der(data)
print(f"digest algorithm: {dd.digest_algorithm_oid}")
print(f"digest: {dd.digest.hex()}")
if dd.encap_content:
    content = dd.encap_content  # raw content bytes
```

---

## AuthenticatedData

`AuthenticatedData` implements RFC 5652 §9 — MAC-authenticated content.

```python
class AuthenticatedData:
    @staticmethod
    def from_der(data: bytes) -> AuthenticatedData: ...
    def to_der(self) -> bytes: ...

    version: int
    originator_info: bytes | None
    recipient_infos: bytes                    # raw RecipientInfos SET bytes
    mac_algorithm_oid: ObjectIdentifier
    mac_algorithm_params: bytes | None
    digest_algorithm_oid: ObjectIdentifier | None
    digest_algorithm_params: bytes | None
    encap_content_type: ObjectIdentifier
    encap_content: bytes | None
    mac: bytes

    auth_attrs: bytes | None
    # Value bytes of the [2] IMPLICIT AuthAttributes (no outer tag/length).
    # To hash for MAC verification, prepend b'\x31' + DER-encoded length header.

    unauth_attrs: bytes | None
    # Value bytes of the [3] IMPLICIT UnauthAttributes (no outer tag/length).
```

### Usage

```python
from synta.cms import AuthenticatedData

ad = AuthenticatedData.from_der(data)
print(f"mac algorithm: {ad.mac_algorithm_oid}")
print(f"mac: {ad.mac.hex()}")

if ad.auth_attrs:
    # auth_attrs contains only the value bytes of the AuthAttributes SET (no outer
    # tag or length).  To compute the MAC input, prepend b'\x31' + a properly
    # DER-encoded length header.  Individual Attribute SEQUENCES can be iterated
    # directly from the value bytes:
    import synta
    dec = synta.Decoder(ad.auth_attrs, synta.Encoding.DER)
    while not dec.is_empty():
        attr_tlv = dec.decode_raw_tlv()
        # each attr_tlv is a complete Attribute SEQUENCE
```

See also [CMS Overview](overview.md) for the complete list of content types.