Create a BIO chain for writing content into a PKCS#7 structure (digest/encrypt filters).
BIO to which application data should be written, or NULL on failure.
| Name | Description |
|---|---|
| p7 | PKCS#7 object being signed, enveloped, digested, or encrypted. |
| bio | Optional BIO supplying detached content, or NULL to embed content in p7. |