PKCS11 Import Encrypted PKCS1 RSA Private Key

Question

I have a simple straight question: Can an encrypted PKCS1 RSAPrivateKey be imported into a PKCS11 compatible security module without exposing the private key in the client's memory?

I know that PKCS11 explicitly mentions PKCS8's PrivateKeyInfo as the required private key format in order to import it in through the C_UnwrapKey function.

Any help please!

Answer 1

Whether private key is exposed in the host memory during the unwrapping fully depends on the implementation of your PKCS#11 module.

RSA keys are usually wrapped with symmetric keys (i.e. AES) and sadly many PKCS#11 modules shipped with common smartcards implement symmetric encryption algorithms in software. Unwrapping in such cases consists of two steps:

1. software based decryption of key material which is stored in the host memory
2. import of decrypted key material into the device

However there are also PKCS#11 implementations (and devices) that implement symmetric encryption algorithms in hardware and these are capable of performing unwrapping of RSA keys without exposing private key into the host memory.

You can use C_GetMechanismInfo() function to find out whether your PKCS#11 module performs specific algorithm in hardware or not. Just examine the "flags" member of returned CK_MECHANISM_INFO structure for the presence of CKF_HW flag.

Edit: PKCS#1 to PKCS#8 conversion

As far as I know PKCS#11 does not specify any standard method for PKCS#1 key unwrapping or conversion. Also the last time I have worked with Luna SA HSM there was a statement in the documentation that it expects imported key material to be in PKCS#8 format.

You can try to convert PKCS#1 key to PKCS#8 in software, but I am afraid it won't be possible without decryption of private key into the host memory. It is rather easy to convert unencrypted PKCS#1 key to the PKCS#8 one - you just insert PKCS#1 RSAPrivateKey sequence into the PKCS#8 PrivateKeyInfo sequence, specify version, privateKeyAlgorithm and you are done. But to convert encrypted PKCS#1 key (whole RSAPrivateKey sequence is encrypted) you first need to decrypt it, convert it to PKCS#8 PrivateKeyInfo sequence, then encrypt PKCS#8 PrivateKeyInfo sequence, insert encrypted PrivateKeyInfo into EncryptedPrivateKeyInfo sequence and specify encryptionAlgorithm.

Answer 2

Yes, you can! Use the pkcs11-tools --keypairgen option to do so.

e.g. pkcs11-tool --module /usr/local/lib/opensc-pkcs11.so -l --pin 648219 --keypairgen --key-type rsa:1024 --id 10

See http://linux.die.net/man/1/pkcs11-tool https://github.com/OpenSC/OpenSC/wiki/SmartCardHSM

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