PKCS#11
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| Cryptographic Token Interface Standard |
PKCS#11 |
Key, MAC and IV derivation in TLS 1.0, denoted CKM_TLS_KEY_AND_MAC_DERIVE, is a mechanism used to derive the appropriate cryptographic keying material used by a "CipherSuite" from the "master_secret" key and random data. This mechanism returns the key handles for the keys generated in the process, as well as the IVs created.
It has a parameter, a CK_SSL3_KEY_MAT_PARAMS structure, which allows for the passing of random data as well as the characteristic of the cryptographic material for the given CipherSuite and a pointer to a structure which receives the handles and IVs which were generated. This structure is defined in Section 12.31.
This mechanism contributes to the creation of four distinct keys on the token and returns two IVs (if IVs are requested by the caller) back to the caller. The keys are all given an object class of CKO_SECRET_KEY.
The two MACing keys ("client_write_MAC_secret" and "server_write_MAC_secret") are always given a type of CKK_GENERIC_SECRET. They are flagged as valid for signing, verification, and derivation operations.
The other two keys ("client_write_key" and "server_write_key") are typed according to information found in the template sent along with this mechanism during a C_DeriveKey function call. By default, they are flagged as valid for encryption, decryption, and derivation operations.
IVs will be generated and returned if the ulIVSizeInBits field of the CK_SSL_KEY_MAT_PARAMS field has a nonzero value. If they are generated, their length in bits will agree with the value in the ulIVSizeInBits field.
All four keys inherit the values of the CKA_SENSITIVE, CKA_ALWAYS_SENSITIVE, CKA_EXTRACTABLE, and CKA_NEVER_EXTRACTABLE attributes from the base key. The template provided to C_DeriveKey may not specify values for any of these attributes which differ from those held by the base key.
Note that the CK_SSL3_KEY_MAT_OUT structure pointed to by the CK_SSL3_KEY_MAT_PARAMS structure's pReturnedKeyMaterial field will be modified by the C_DeriveKey call. In particular, the four key handle fields in the CK_SSL3_KEY_MAT_OUT structure will be modified to hold handles to the newly-created keys; in addition, the buffers pointed to by the CK_SSL3_KEY_MAT_OUT structure's pIVClient and pIVServer fields will have IVs returned in them (if IVs are requested by the caller). Therefore, these two fields must point to buffers with sufficient space to hold any IVs that will be returned.
This mechanism departs from the other key derivation mechanisms in Cryptoki in its returned information. For most key-derivation mechanisms, C_DeriveKey returns a single key handle as a result of a successful completion. However, since the CKM_SSL3_KEY_AND_MAC_DERIVE mechanism returns all of its key handles in the CK_SSL3_KEY_MAT_OUT structure pointed to by the CK_SSL3_KEY_MAT_PARAMS structure specified as the mechanism parameter, the parameter phKey passed to C_DeriveKey is unnecessary, and should be a NULL_PTR.
If a call to C_DeriveKey with this mechanism fails, then none of the four keys will be created on the token.