UnwrapKey
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SYNOPSIS
# include <cssm.h>
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API PARAMETERS
| CCHandle (input) | The handle that describes the context of this cryptographic operation. | |
| PublicKey (input/optional) | ||
The public key corresponding to the private key being unwrapped. If a symmetric key is being unwrapped, then this parameter must be NULL. | ||
| WrappedKey (input) | ||
A pointer to the wrapped key. The wrapped key may be a symmetric key or the private key of a public/private key pair. The unwrapping method is specified as meta data within the wrapped key and is not specified outside of the wrapped key. | ||
| KeyUsage (input) | A bit mask indicating all permitted uses for the unwrapped key. If no value is specified, the CSP defines the usage mask for the unwrapped key. | |
| KeyAttr (input) | A bit mask defining other attribute values to be associated with the unwrapped key. | |
| KeyLabel (input/optional) | ||
Pointer to a byte string that will be used as the label for the unwrapped key. | ||
| CredAndAclEntry (input/optional) | ||
A structure containing one or more credentials authorized for creating a key and the prototype ACL entry that will control future use of the newly created key. The credentials and ACL entry prototype can be presented as immediate values or callback functions can be provided for use by the CSP to acquire the credentials and/or the ACL entry interactively. If the CSP provides public access for creating a key, then the credentials can be NULL. If the CSP defines a default initial ACL entry for the new key, then the ACL entry prototype can be an empty list. | ||
| UnwrappedKey (output) | ||
A pointer to a CSSM_KEY structure that returns the unwrapped key. | ||
| DescriptiveData (output) | ||
A pointer to a CSSM_DATA structure that returns any additional descriptive data that was associated with the key during the wrapping operation. It is assumed that the caller incorporated knowledge of the structure of this data. If no additional data is associated with the imported key, this output value is NULL. | ||
SPI PARAMETERS
| CSPHandle (input) | ||
The handle that describes the add-in Cryptographic Service Provider module used to perform up calls to CSSM for the memory functions managed by CSSM. | ||
| CCHandle (input) | The handle that describes the context of this cryptographic operation. | |
| Context (input) | Pointer to CSSM_CONTEXT structure that describes the attributes with this context. | |
| Privilege (input) | ||
The export privilege to be applied during the cryptographic operation. This parameter is forwarded to the CSP after CSSM verifies the caller and service provider privilege set includes the specified PRIVILEGE. | ||
DESCRIPTION
This function unwraps the wrapped key using the context. The wrapped key can be a symmetric key or a private key. If the unwrapping algorithm is a symmetric algorithm, then a symmetric context must be provided. If the unwrapping algorithm is an asymmetric algorithm, then an asymmetric context must be provided. If the key is a private key, then an asymmetric context must be provide describing the unwrapping algorithm. The CSP can require the caller to provide credentials authorizing the caller to store the unwrapped key within the CSP. The CSP can also require that the caller provide an initial ACL entry to control future access to the newly stored key. These credentials and the initial ACL entry value are provided in CredAndAclEntry parameter. If the unwrapping algorithm is CSSM_ALGID_NONE and the wrapped key is actually a raw key (as indicated by its key attributes), then the key is imported into the CSP. Support for a CSSM_ALGID_NONE unwrapping algorithm is at the option of the CSP. The unwrapped key is restored to its original pre-wrap state based on the key attributes recorded by the wrapped key during the wrap operation. These attributes must not be modified by the caller.
Authorization policy can restrict the set of callers who can create a new resource. In this case, the caller must present a set of access credentials for authorization. Upon successfully authenticating the credentials, the template that verified the presented samples identifies the ACL entry that will be used in the authorization computation. If the caller is authorized, the new resource is created.
The caller must provide an initial ACL entry to be associated with the newly created resource. This entry is used to control future access to the new resource and (since the subject is deemed to be the "Owner") exercise control over its associated ACL. The caller can specify the following items for initializing an ACL entry:
Subject - A CSSM_LIST structure, containing the type of the subject and a template value that can be used to verify samples that are presented in credentials when resource access is requested.
Delegation flag - A value indicating whether the Subject can delegate the permissions recorded in the AuthorizationTag. (This item only applies to public key subjects).
Authorization tag - The set of permissions that are granted to the Subject.
Validity period - The start time and the stop time for which the ACL entry is valid.
ACL entry tag - A user-defined string value associated with the ACL entry.
The service provider can modify the caller-provided initial ACL entry to conform to any innate resource-access policy that the service provider may be required to enforce. If the initial ACL entry provided by the caller contains values or permissions that are not supported by the service provider, then the service provider can modify the initial ACL appropriately or can fail the request to create the new resource. Service providers list their supported AuthorizationTag values in their Module Directory Services primary record.
NOTES
The KeyData field of the CSSM_KEY structure is allocated by the CSP. The application is required to free this memory using the CSSM_FreeKey() (CSSM API), or CSP_FreeKey() (CSP SPI), function or with the memory functions registered for the CSPHandle.
RETURN VALUE
A CSSM_RETURN value indicating success or specifying a particular error condition. The value CSSM_OK indicates success. All other values represent an error condition.