How to get public key from private key in PKCS #11

[Wei-Jun Wang]

So are you suggesting there is no such a way?

I do notice that in NSS’s own HPKE implementation, the receiver needs to provide both keys [1]:

SECStatus PK11_HPKE_SetupR(HpkeContext *cx, const SECKEYPublicKey *pkR, SECKEYPrivateKey *skR,
                           const SECItem *enc, const SECItem *info);

Maybe they also don’t have a simple way to get pkR from skR.

Thanks,
Weijun

[1] https://github.com/nss-dev/nss/blob/e2f270997ff9364aebb688f49b7c28698b70f24d/lib/pk11wrap/pk11pub.h#L788

On Dec 9, 2024, at 21:27, Francisco Ferrari Bihurriet <fferrari at redhat.com> wrote:

Hi Wei-Jun,

As far as I know, public and private keys are different PKCS#11 objects,
each one with a different CK_OBJECT_HANDLE. See for example how
C_GenerateKeyPair [1] has two output parameters: CK_OBJECT_HANDLE_PTR
phPublicKey amd CK_OBJECT_HANDLE_PTR phPrivateKey.

NSS uses CKA_PUBLIC_KEY_INFO only when wrapping [2] / unwrapping [3]
(C_WrapKey / C_UnwrapKey) RSA-PSS keys (where it stores an ASN1-encoded
SubjectPublicKeyInfo with the algorithm OID and the DER encoding of the
public key).

Here [4] is how SunPKCS11 proceeds after calling C_GenerateKeyPair, by
creating two P11Key objects for each handle (P11PublicKey and
P11PrivateKey).

[1] https://urldefense.com/v3/__https://docs.oasis-open.org/pkcs11/pkcs11-base/v3.0/pkcs11-base-v3.0.html*_Toc29976704__;Iw!!ACWV5N9M2RV99hQ!OmuwCcv-dJsqSgUuLEW8yqzvuB4Qwj5ay4afqgvAfvn3DiGx9lz31XjKDuAt_LABjdrwdCT8FmTTLO6ARjM$
[2] https://urldefense.com/v3/__https://github.com/nss-dev/nss/blob/NSS_3_101_RTM/lib/softoken/pkcs11c.c*L6038-L6039__;Iw!!ACWV5N9M2RV99hQ!OmuwCcv-dJsqSgUuLEW8yqzvuB4Qwj5ay4afqgvAfvn3DiGx9lz31XjKDuAt_LABjdrwdCT8FmTT9ztKx9Y$
[3] https://urldefense.com/v3/__https://github.com/nss-dev/nss/blob/NSS_3_101_RTM/lib/softoken/pkcs11c.c*L6604-L6605__;Iw!!ACWV5N9M2RV99hQ!OmuwCcv-dJsqSgUuLEW8yqzvuB4Qwj5ay4afqgvAfvn3DiGx9lz31XjKDuAt_LABjdrwdCT8FmTTdVw8oI8$
[4] https://urldefense.com/v3/__https://github.com/openjdk/jdk/blob/jdk-25*1/src/jdk.crypto.cryptoki/share/classes/sun/security/pkcs11/P11KeyPairGenerator.java*L424-L431__;KyM!!ACWV5N9M2RV99hQ!OmuwCcv-dJsqSgUuLEW8yqzvuB4Qwj5ay4afqgvAfvn3DiGx9lz31XjKDuAt_LABjdrwdCT8FmTTozigB-E$

Regards,
--
Francisco

On 12/10/24 01:43, Wei-Jun Wang wrote:
Daniel suggested CKA_PUBLIC_KEY_INFO but it’s not available in NSS 3.101.

On Dec 9, 2024, at 08:07, Wei-Jun Wang <weijun.wang at oracle.com> wrote:

Hi PKCS #11 gurus,

DHKEM [1] requires a function

 Pk(skX): The KEM public key corresponding to the KEM private key skX.

"The notation pk(skX), depending on its use and the KEM and its
implementation, is either the computation of the public key using the
private key, or just syntax expressing the retrieval of the public
key, assuming it is stored along with the private key object."

For the software side, I can calculate the public key [2] from the
private key. How can I do this in PKCS #11?

Thanks,
Weijun

[1] https://urldefense.com/v3/__https://www.rfc-editor.org/rfc/rfc9180.html*name-notation__;Iw!!ACWV5N9M2RV99hQ!OmuwCcv-dJsqSgUuLEW8yqzvuB4Qwj5ay4afqgvAfvn3DiGx9lz31XjKDuAt_LABjdrwdCT8FmTT0-STk6s$
[2] https://urldefense.com/v3/__https://github.com/openjdk/jdk/blob/__;!!ACWV5N9M2RV99hQ!OmuwCcv-dJsqSgUuLEW8yqzvuB4Qwj5ay4afqgvAfvn3DiGx9lz31XjKDuAt_LABjdrwdCT8FmTTH8KrINU$
adca97b659d725b0dd320322297dcbd1b443a047/src/java.base/share/classes/
sun/security/ec/ECPrivateKeyImpl.java#L209

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