pico-hsm/doc/asymmetric-ciphering.md

Asymmetric encryption and decryption

Pico HSM supports in place decryption with the following algorithms:

• RSA-PKCS
• RSA-X-509

First, we generate the data:

$ echo "This is a test string. Be safe, be secure." > data

Obtain the public key and convert it to PEM format:

$ pkcs11-tool --read-object --pin 648219 --id 1 --type pubkey > 1.der
$ openssl rsa -inform DER -outform PEM -in 1.der -pubin > 1.pub

At this moment, you are able to verify with the public key in 1.pub. The signature is computed inside the Pico HSM with the private key. It never leaves the device.

RSA-PKCS

First, we encrypt the data with the public key:

$ openssl rsautl -encrypt -inkey 1.pub -in data -pubin -out data.crypt

Then, we decrypt with the private key inside the Pico HSM:

$ cat data.crypt | pkcs11-tool --id 1 --pin 648219 --decrypt --mechanism RSA-PKCS
Using slot 0 with a present token (0x0)
Using decrypt algorithm RSA-PKCS
This is a test string. Be safe, be secure.

RSA-X-509

In this algorithm, the data must be padded with a length equal to the size of private key (128, 256, 512 bytes for RSA-1024, RSA-2048 and RSA-4096, respectively).

First, we pad the data. The original data file occupies 29 bytes. Thus, for a 2048 bits key, a padding of 227 bytes is needed:

$ cp data data_pad
$ dd if=/dev/zero bs=1 count=227 >> data_pad

we encrypt the data with the public key:

$ openssl rsautl -encrypt -inkey 1.pub -in data_pad -pubin -out data.crypt -raw

Then, we decrypt with the private key inside the Pico HSM:

$ cat data.crypt|pkcs11-tool --id 4 --pin 648219 --decrypt --mechanism RSA-X-509 
Using slot 0 with a present token (0x0)
Using decrypt algorithm RSA-X-509
This is a test string. Be safe, be secure.