DeriveKey

NAME

CSSM_DeriveKey, CSP_DeriveKey — Derive new symmetric key (CDSA)

SYNOPSIS

# include <cssm.h>

API:
CSSM_RETURN CSSMAPI CSSM_DeriveKey
(CSSM_CC_HANDLE CCHandle,
CSSM_DATA_PTR Param,
uint32 KeyUsage,
uint32 KeyAttr,
const CSSM_DATA *KeyLabel,
const CSSM_RESOURCE_CONTROL_CONTEXT *CredAndAclEntry,
CSSM_KEY_PTR DerivedKey)
SPI:
CSSM_RETURN CSSMCSPI CSP_DeriveKey
(CSSM_CSP_HANDLE CSPHandle,
CSSM_CC_HANDLE CCHandle,
const CSSM_CONTEXT *Context,
CSSM_DATA_PTR Param,
uint32 KeyUsage,
uint32 KeyAttr,
const CSSM_DATA *KeyLabel,
const CSSM_RESOURCE_CONTROL_CONTEXT *CredAndAclEntry,
CSSM_KEY_PTR DerivedKey)

LIBRARY

Common Security Services Manager library (cdsa$incssm300_shr.exe)

API PARAMETERS

`CCHandle` (`input`)		The handle that describes the context of this cryptographic operation.
`Param` (input/output)
		This parameter varies depending on the derivation algorithm. Password based derivation algorithms use this parameter to return a cipher block chaining initialization vector. Concatenation algorithms use this parameter to get the second item to concatenate.
`KeyUsage` (`input`)		A bit mask indicating all permitted uses for the new derived key.
`KeyAttr` (`input`)		A bit mask defining other attribute values for the new derived key.
`KeyLabel` (input/optional)
		Pointer to a byte string that will be used as the label for the derived 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 subject of 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 empty.
`DerivedKey` (`output`)
		A pointer to a CSSM_KEY structure that returns the derived key.

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.
`Context` (`input`)		Pointer to CSSM_CONTEXT structure that describes the attributes with this context.

DESCRIPTION

This function derives a new symmetric key using the context and/or information from the base key in the context. The CSP can require that the cryptographic context include access credentials for authentication and authorization checks when using a private key or a secret key.

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. The CSP can require that the cryptographic context include access credentials for authentication and authorization checks when using a private key or a secret key.

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.

ERRORS

Errors are described in the CDSA Technical Standard.

CSSMERR_CSP_KEY_LABEL_ALREADY_EXISTS

COMMENTS

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) call, or with the memory functions registered for the CSPHandle.

DeriveKey

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