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Re: [Opensc-devel] Implementing C_WrapKey and C_UnwrapKey to OpenSC
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From: Douglas E E. <dee...@gm...> - 2017-09-22 18:30:05
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On 9/22/2017 8:32 AM, Aventra Development wrote: > Hi, > > I have committed the first version of C_UnwrapKey implementation to my branch at https://github.com/hhonkanen/OpenSC/tree/wrapping > > I hope you would have time to take a look. > > As we don’t yet even have a card that could perform the actual unwrapping operation, this code is not yet complete and it currently emulates unwrapping by doing a normal decrypt operation. It can be > run and it goes all the way to the card driver when target object template has CKA_TOKEN=FALSE, but the code to store the pkcs#15 object is not yet complete. Anyway, from this commit you can see the > logic I am planning to use. I assume the above is just for testing. In either case if you can support both token and session objects that would be good. Also keep in mind some card drivers emulate some of the PKCS#15 operations, which usually means they can support session objects but not token objects. (The may support token objects but not via PKCS#11 or PKCS#15 but some other means. The OpenSC C_DeriveKey was written for such a card to support ECDH.) CKA_TOKEN=FALSE says the object is a session object which does not require any code to store the pkcs#15 object. CKA_TOKEN=TRUE says the object is a token object, so you would need to tell the token what to do with it. > > This implementation follows the same pattern as C_DeriveKey. The call goes for PKCS#11 to the driver like this: > > 1. C_UnwrapKey --> sc_create_object->pkcs15_create_object, to create the target PKCS#15 object to receive the key. > > pkcs15_create_secret_key calls pkcs15init to create the PKCS#15 structure and key EF on card. > > 2. We have a handle to the target object. From now on the calls go in very similar way like a decrypt or key derivation operation: > > C_UnwrapKey --> sc_pkcs11_unwrap->sc_pkcs11_unwrap_operation->pkcs15_prkey_unwrap->sc_pkcs15_unwrap. > > Here we format and set security environment and call card: > > use_key->sc_set_security_env > > use_key->sc_unwrap->myeid_unwrap_key. > > Before I started coding, I thought of two alternative ways: > > 1. Implement most of the stuff in pkcs15init as you suggested and create new pkcs15init operations > 2. Go C_DeriveKey style. > > It was not an easy decision, but the main motives to go C_DeriveKey way were: Good choice I like the C_DeriveKey choice especially for cards that are not true PKCS#15 cards. > > * I noticed that after we have a target key object, the rest of the operation is actually similar to decrypt. The unwrapping operation is performed with a PKCS#11 key object, which supports specific > mechanisms. This initial version supports only RSA, but in future we could have several mechanism for each supported key type, for example CKM_AES_ECB, CKM_AES_CBC, CKM_RSA_PKCS, CKM_RSA_X_509 > etc. The logic to handle a crypto operations with a specific object and a mechanism was already there. > * there already was unwrap_key method defined in sc_pkcs11_object_ops. > * there already was the working C_DeriveKey code. I thought it would be good to be consistent with it, because it does nearly the same thing. > * I think this model fits for C_WrapKey as well. As a crypto operation it has the same characteristics, the data just goes into other direction. > > We haven’t yet decided how to tell driver and card, which key file should receive the unwrapped key. We have thought of using manage security environment, but haven’t yet find a card independent way > to set it in pkcs15-sec.c. > You could use the CKA_LABEL, or even a vendor supplied attribute for OpenSC, that could be used to pass info to pkcs15init when creating a key on the card. Side issue:OpenSC needs to fix how it assigns CKA_VENDOR_DEFINED attributes. see: https://github.com/OpenSC/OpenSC/pull/1131#issuecomment-323335738 For session keys, the handle to the key is good enough since the handle is unique for the session. > Another thing we have to think about is do we need to implement a new function in pkcs15init/pkcs15-lib.c to create an empty secret key file to receive the unwrapped key. There is a function to store > a secret key: sc_pkcs15init_store_secret_key, but it doesn’t currently work without key data. > > I am really looking forward to find such architecture that the community can accept and to have the code merged into master when it’s functional. Hoping to hear opinions on is this as good way to go > or should we take a different approach. > > - Hannu > > *Lähettäjä:*Frank Morgner [mailto:fra...@gm...] > *Lähetetty:* maanantai 18. syyskuuta 2017 0.27 > *Vastaanottaja:* Aventra Development <dev...@av...> > *Kopio:* ope...@li... > *Aihe:* Re: [Opensc-devel] Implementing C_WrapKey and C_UnwrapKey to OpenSC > > OK, we'll see when you're fine with some working code. > > One more pointer I'd like to give is ISO 7816-8, which gives some example on how to import a private key using PUT DATA with DO 7F48 (card holder private key template). As far as I know, OpenSC used > to implement the ISO style of card interactions first, which then got mapped to other type of cards as well. So using the existing get_data and put_data hooks of the card driver would also be usable > for key import. That being said, I know that the concept has been softened. There is the read_public_key callback, which following the ISO style should have been implemented with get_data... > > 2017-09-14 14:10 GMT+02:00 Aventra Development <dev...@av... <mailto:dev...@av...>>: > > Thank you for your comments! > > I have got quite far in implementing the first case of C_UnwrapKey that we need, which is unwrapping a secret key using an RSA key. During coding I have also realized that at least the part that > creates the PKCS#15 object for the unwrapped key, adds it to SKDF and updates it to the card belongs naturally to pkcs15init. However, the part that performs the crypto operation to unwrap the key > is very similar to decrypt and derive operations, so I ended up adding sc_pkcs15_unwrap() to pkcs15-sec.c. So in my current implementation what happens is: > > 1. The call to C_UnwrapKey is first handled in pkcs#11 level (pkcs11-object.c and mechanism.c) > 2. Via sc_pkcs11_object_ops we get into framework_pkcs15, I have added a function named pkcs15_prkey_unwrap() > 3. I use sc_pkcs15init_bind like in some other framework_pkcs15 functions, and call pkcs15init. I have added a new function sc_pkcs15init_unwrap_key() > 4. sc_pkcs15init_unwrap_key() creates the new key object (key EF) into card, updates SKDF, and calls sc_pkcs15_unwrap() in pkcs15-sec.c to perform the actual crypto operation on card. > 5. The card performs a decrypt operation and places the result into the key EF created by pkcs15init. (we don’t have this feature on card yet). > > In driver level I initially added wrap and unwrap operations to sc_card_operations. I don’t have a strong opinion on which is better, this way or using sc_card_ctl. Still I think they fit quite > well on the same level with decipher and compute_signature operations. But in the whole job this is actually a minor detail and can still be changed easily. > > I am still not sure, can we do this in a way that is card independent enough in pkcs15-sec, or would it be better to implement a new pkcs15init operation (a new function pointer to > > sc_pkcs15init_operations) which each card vendor could implement in their own way. We’ll see how it looks as I progress. > > When I get my code in buildable and more solid state, I’ll commit it into my fork and you could take a look. > > Got to keep the minidriver spec in mind. I am not very familiar on how the OpenSC minidriver interacts with rest of OpenSC, and I hope this doesn’t add too much complexity into my implementation. > Probably the important thing is to make the low level implementation on card driver level usable with both minidriver and PKCS#11 way, because in higher level a parallel implementation could be > added for the minidriver. > > - Hannu > > *Lähettäjä:*Frank Morgner [mailto:fra...@gm... <mailto:fra...@gm...>] > *Lähetetty:* torstai 14. syyskuuta 2017 11.16 > *Vastaanottaja:* Aventra Development <dev...@av... <mailto:dev...@av...>> > *Kopio:* ope...@li... <mailto:ope...@li...> > > > *Aihe:* Re: [Opensc-devel] Implementing C_WrapKey and C_UnwrapKey to OpenSC > > In general your approach sounds good! But I have objections regarding the software architecture. Historically, key generation and key import has been done in pkcs15init. There are some other cards > besides sc-hsm that are calling some control command in the card driver from pkcs15init. Basically, what you're asking for is to use pkcs15init functionality in PKCS#11. Instead of implementing > everything in PKCS#11, it would be better to make pkcs15init available as DLL/LIB that can be loaded into OpenSC's PKCS#11 library. With this approach you would implement key wrapping in your > card's operations in pkcs15init (possibly redirecting it to the driver in libopensc with a control command). > > One more thing I'd like to throw in is that Microsoft also has its view of key wrapping. Have a look at Smart Card Minidriver Specification, v7.07 Figure B1. Process for key generation and > insertion (https://msdn.microsoft.com/en-us/library/windows/hardware/dn631754(v=vs.85).aspx). Please make sure that your implementation has this spec in mind so that key wrapping can also be added > to the minidriver. > > Regards, > > Frank. > > 2017-09-11 10:11 GMT+02:00 Aventra Development <dev...@av... <mailto:dev...@av...>>: > > Thanks for the tip. Yes, the ECDH code looks like it can be used with slight modifications and expanded to perform unwrap. Some more work is needed in the card/driver level to set up > properties of the new key in the key EF on card according to the PKCS#11 attributes in the template. > > What do you think about adding wrap and unwrap into sc_card_operations in opensc.h? Is there a risk of causing some trouble or should all go fine as long they're just set to NULL on cards that > don't support them? If more cards would support these operations in future, this way each card wouldn't need to add new card specific SC_CARDCTL_xxx values. > > - Hannu > > -----Alkuperäinen viesti----- > Lähettäjä: Douglas E Engert [mailto:dee...@gm... <mailto:dee...@gm...>] > Lähetetty: perjantai 8. syyskuuta 2017 15.26 > Vastaanottaja: ope...@li... <mailto:ope...@li...> > Aihe: Re: [Opensc-devel] Implementing C_WrapKey and C_UnwrapKey to OpenSC > > > The ECDH can derive a key, which may be returned by the card or kept on the card. > A Session object is created for the derived key. The code was written for a card that would return a secret key so the session object has CKA_TOKEN=FALSE. > > So the derive code is very similar to the unwrap. You might want to start looking it. > > > On 9/8/2017 6:32 AM, Aventra Development wrote: > > Hi fellow OpenSC developers, > > > > Some of you may already know me from my contributions to mostly MyEID > > driver. We are now starting a larger development project so I thought > > a brief introduction would be appropriate. I am a developer at Aventra, Finland. Our target in this project is to implement C_WrapKey and C_UnwrapKey PKCS#11 functions into OpenSC and > initially to the MyEID driver. At the same time we are going to implement this functionality into MyEID card. > > > > I have created a branch named "wrapping" in my OpenSC fork at > > https://github.com/hhonkanen/OpenSC > > > > Before starting coding I have done some planning and split the work into sub tasks. Here are the tasks I have found: > > > > - implement wrapping and unwarpping in pkcs#15 level > > (framework-pkcs15.c) > > > > * sc_pkcs11_object_ops already contains unwrap_key operation. wrap_key operation must be added. > > > > * implement pkcs15_skey_wrap_key, pkcs15_skey_unwrap_key etc...in framework_pkcs15.c and map the functions to sc_pkcs11_object_ops. > > > > * changes to register_mechamisms and functions called from there (for example sc_pkcs11_new_fw_mechanism). > > > > set CKF_WRAP and CKF_UNWRAP when appropriate. > > > > * parse the CKA_xxxx attributes and create > > the needed PKCS#15 structures for the keys that will be created on > > card during unwrapping operations > > > > - implement wrapping and unwrapping in pkcs15-sec and card driver level: > > > > * add wrap/unwrap functions to sc_card_driver. In SC-HSM driver these are implemented as driver specific card_ctl commands. > > > > I am not sure if we should go this way or add the new operations directly to sc_card_operations. > > > > * implement them in card-myeid.c > > > > * seems like I have to create functions like sc_pkcs15_wrap_key and sc_pkcs15_unwrap_key to do the work between pkcs15 and card layers. > > > > - implement the functions in PKCS#11 level: > > > > * implement C_WrapKey and C_UnwrapKey in > > pkcs11-object.c. Check mechanism and attributes and call > > framework_pkcs15 > > > > * return the handle of wrapped key (in memory) or unwrapped key (on card) to the pkcs#11 level and to the caller. > > > > Some issues we have to think about: > > > > - It is still not totally clear to me how to begin implementing the > > operations from PKCS#11 side (C_WrapKey and C_UnwrapKey in pkcs11-object.c). I think I am going to follow a similar pattern as in C_SignInit and C_DecryptInit. This will probably become > clearer when I get started, but any tips are more than welcome. > > > > - Handling of secret key objects when CKA_TOKEN=FALSE. PKCS#11 doesn't > > define where such session objects should be stored, but leaves it up > > to implementation. We must have possibililty to have session objects on card. With this I mean key objects that are cleaned from the card in the next reset and the key material never leaves > the card. We need this kind of objects in chained key wrapping operation. I am planning to implement it so that drivers could tell whether they can handle in card session objects. If a driver > doesn't support them, they would be handled as in memory objects. > > > > - in addition to RSA and AES keys, we must be able to handle > > CKK_GENERIC_SECRET objects which might be somewhat different to implement, because lots of the key handling code is related to the key algorithm. > > > > Any feedback, tips and contributions in testing/code review will be greatly appreciated. > > > > Best regards, > > > > Hannu Honkanen > > > > Aventra > > > > > > > > ---------------------------------------------------------------------- > > > -------- Check out the vibrant tech community on one of the world's > > > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > > > > > > > _______________________________________________ > > Opensc-devel mailing list > > Ope...@li... <mailto:Ope...@li...> > > https://lists.sourceforge.net/lists/listinfo/opensc-devel > > > > -- > > Douglas E. Engert <DEE...@gm... <mailto:DEE...@gm...>> > > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ > Opensc-devel mailing list > Ope...@li... <mailto:Ope...@li...> > https://lists.sourceforge.net/lists/listinfo/opensc-devel > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Opensc-devel mailing list > Ope...@li... <mailto:Ope...@li...> > https://lists.sourceforge.net/lists/listinfo/opensc-devel > > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Opensc-devel mailing list > Ope...@li... <mailto:Ope...@li...> > https://lists.sourceforge.net/lists/listinfo/opensc-devel > > > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > > > _______________________________________________ > Opensc-devel mailing list > Ope...@li... > https://lists.sourceforge.net/lists/listinfo/opensc-devel > -- Douglas E. Engert <DEE...@gm...> |
