provider-object - A specification for a provider-native object abstraction
#include <openssl/core_object.h>
#include <openssl/core_names.h>The provider-native object abstraction is a set of OSSL_PARAM(3) keys and values that can be used to pass provider-native objects to OpenSSL library code or between different provider operation implementations with the help of OpenSSL library code.
The intention is that certain provider-native operations can pass any sort of object that belong with other operations, or with OpenSSL library code.
An object may be passed in the following manners:
By value
This means that the object data is passed as an octet string or an UTF8 string, which can be handled in diverse ways by other provided implementations. The encoding of the object depends on the context it's used in; for example, OSSL_DECODER(3) allows multiple encodings, depending on existing decoders. If central OpenSSL library functionality is to handle the data directly, it must be encoded in DER for all object types except for OSSL_OBJECT_NAME (see "Parameter reference" below), where it's assumed to a plain UTF8 string.
By reference
This means that the object data isn't passed directly, an object reference is passed instead. It's an octet string that only the correct provider understands correctly.
Objects by value can be used by anything that handles DER encoded objects.
Objects by reference need a higher level of cooperation from the implementation where the object originated (let's call it X) and its target implementation (let's call it Y):
An object loading function in the target implementation
The target implementation (Y) may have a function that can take an object reference. This can only be used if the target implementation is from the same provider as the one originating the object abstraction in question (X).
The exact target implementation to use is determined from the object type and possibly the object data type. For example, when the OpenSSL library receives an object abstraction with the object type OSSL_OBJECT_PKEY, it will fetch a provider-keymgmt(7) using the object data type as its key type (the second argument in EVP_KEYMGMT_fetch(3)).
An object exporter in the originating implementation
The originating implementation (X) may have an exporter function. This exporter function can be used to export the object in OSSL_PARAM(3) form, that can then be imported by the target implementation's imported function.
This can be used when it's not possible to fetch the target implementation (Y) from the same provider.
A provider-native object abstraction is an OSSL_PARAM(3) with a selection of the following parameters:
The object data passed by value.
The object data passed by reference.
The object type, a number that may have any of the following values (all defined in <openssl/core_object.h>):
The object data may only be passed by value, and should be a UTF8 string.
This is useful for provider-storemgmt(7) when a URI load results in new URIs.
The object data is suitable as provider-native EVP_PKEY key data. The object data may be passed by value or passed by reference.
The object data is suitable as X509 data. The object data for this object type can only be passed by value, and should be an octet string.
Since there's no provider-native X.509 object, OpenSSL libraries that receive this object abstraction are expected to convert the data to a X509 object with d2i_X509().
The object data is suitable as X509_CRL data. The object data can only be passed by value, and should be an octet string.
Since there's no provider-native X.509 CRL object, OpenSSL libraries that receive this object abstraction are expected to convert the data to a X509_CRL object with d2i_X509_CRL().
The specific type of the object content. Legitimate values depend on the object type; if it is OSSL_OBJECT_PKEY, the data type is expected to be a key type suitable for fetching a provider-keymgmt(7) that can handle the data.
The outermost structure of the object content. Legitimate values depend on the object type.
A human readable text that describes extra details on the object.
When a provider-native object abstraction is used, it must contain object data in at least one form (object data passed by value, i.e. the "data" item, or object data passed by reference, i.e. the "reference" item). Both may be present at once, in which case the OpenSSL library code that receives this will use the most optimal variant.
For objects with the object type OSSL_OBJECT_NAME, that object type must be given.
The concept of providers and everything surrounding them was introduced in OpenSSL 3.0.
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