Concatenation of a base key and another key

This mechanism, denoted CKM_CONCATENATE_BASE_AND_KEY, derives a secret key from the concatenation of two existing secret keys. The two keys are specified by handles; the values of the keys specified are concatenated together in a buffer.

This mechanism takes a parameter, a CK_OBJECT_HANDLE. This handle produces the key value information which is appended to the end of the base key's value information (the base key is the key whose handle is supplied as an argument to C_DeriveKey).

For example, if the value of the base key is 0x01234567, and the value of the other key is 0x89ABCDEF, then the value of the derived key will be taken from a buffer containing the string 0x0123456789ABCDEF.

If no length or key type is provided in the template, then the key produced by this mechanism will be a generic secret key. Its length will be equal to the sum of the lengths of the values of the two original keys.
If no key type is provided in the template, but a length is, then the key produced by this mechanism will be a generic secret key of the specified length.
If no length is provided in the template, but a key type is, then that key type must have a well-defined length. If it does, then the key produced by this mechanism will be of the type specified in the template. If it doesn't, an error will be returned.
If both a key type and a length are provided in the template, the length must be compatible with that key type. The key produced by this mechanism will be of the specified type and length. If a DES, DES2, DES3, or CDMF key is derived with this mechanism, the parity bits of the key will be set properly.

If the requested type of key requires more bytes than are available by concatenating the two original keys' values, an error is generated.

This mechanism has the following rules about key sensitivity and extractability:

If either of the two original keys has its CKA_SENSITIVE attribute set to CK_TRUE, so does the derived key. If not, then the derived key's CKA_SENSITIVE attribute is set either from the supplied template or from a default value.
Similarly, if either of the two original keys has its CKA_EXTRACTABLE attribute set to CK_FALSE, so does the derived key. If not, then the derived key's CKA_EXTRACTABLE attribute is set either from the supplied template or from a default value.
The derived key's CKA_ALWAYS_SENSITIVE attribute is set to CK_TRUE if and only if both of the original keys have their CKA_ALWAYS_SENSITIVE attributes set to CK_TRUE.
Similarly, the derived key's CKA_NEVER_EXTRACTABLE attribute is set to CK_TRUE if and only if both of the original keys have their CKA_NEVER_EXTRACTABLE attributes set to CK_TRUE.

RSA Security Inc. Public-Key Cryptography Standards - PKCS#11 - v220