With PyKCS11 I provide a sample code
signature.py
to compute a RSA+SHA256 signature. The Python sample also contains the code to
check the signature using PyKCS11.
But what if you want to verify the signature using OpenSSL?
Export the public key
PYKCS11LIB environment variable is used to indicate what PKCS#11 library to
use. For the tests I use
SoftHSM so I set the variable using:
$ export PYKCS11LIB=/usr/local/lib/softhsm/libsofthsm2.so
#!/bin/bash
set -e
# get the 1st key object ID
ID=$(pkcs11-tool --module $PYKCS11LIB --list-objects --type pubkey \
| grep ID \
| cut -d: -f 2)
echo "Object id: $ID"
# export the public key
pkcs11-tool --module $PYKCS11LIB --read-object --type pubkey --id $ID -o rsa_pub.key
# convert the public key to PEM
openssl rsa -pubin -inform DER -in rsa_pub.key -outform PEM -out rsa_pub.pem
The RSA key pair has been generated by the
generate.py
script and is stored in the PKCS#11 token. We need to export it so that
OpenSSL can use it to check the signature.
To export the key I use pkcs11-tool from the
OpenSC project. We need to know
the object ID of the public key. This ID is configured in generate.py script
line 22. We dump the public keys and get the object ID.
$ pkcs11-tool --module $PYKCS11LIB --list-objects --type pubkey
Using slot 0 with a present token (0x27ca3aa)
Public Key Object; RSA 1024 bits
label: My Public Key
ID: 22
Usage: encrypt, verify, wrap
Access: local
The script will work correctly if only one public key is present in the token.
I let you handle more complex cases.
output
$ ./export_key.sh
Using slot 0 with a present token (0x27ca3aa)
Object id: 22
Using slot 0 with a present token (0x27ca3aa)
writing RSA key
Compute signature
I modified the original signature.py script to also save the clear text
message in a file cleartext.txt and the signature in a file
sig_sha256.bin so these files can be used later by OpenSSL.
#!/usr/bin/env python3
from PyKCS11 import *
import binascii
pkcs11 = PyKCS11Lib()
pkcs11.load() # define environment variable PYKCS11LIB=YourPKCS11Lib
# get 1st slot
slot = pkcs11.getSlotList(tokenPresent=True)[0]
session = pkcs11.openSession(slot, CKF_SERIAL_SESSION | CKF_RW_SESSION)
session.login("1234")
# message to sign
toSign = "Hello World!\n"
mechanism = Mechanism(CKM_SHA256_RSA_PKCS, None)
# find first private key and compute signature
privKey = session.findObjects([(CKA_CLASS, CKO_PRIVATE_KEY)])[0]
signature = session.sign(privKey, toSign, mechanism)
print("\nsignature: {}".format(binascii.hexlify(bytearray(signature))))
# save the clear text in a file
with open("cleartext.txt", "w") as f:
f.write(toSign)
# save to a signature in a file
with open("sig_sha256.bin", "bw") as f:
f.write(bytearray(signature))
# find first public key and verify signature
pubKey = session.findObjects([(CKA_CLASS, CKO_PUBLIC_KEY)])[0]
result = session.verify(pubKey, toSign, signature, mechanism)
print("\nVerified:", result)
# logout
session.logout()
session.closeSession()
Output
$ ./signature.py
signature: b'322c1591cb9aba1e361264b02464a2bd9d55693bf772b4253da0862616e611dc139005742c511795c27c8f609e4ddbaafceba1c3b3ce278b8e0af564c84de54a639cff67a9a3f97dcc542cd6f0200954ef7fce4a0f87b61636272e21fc1e3ef9f0b683e360cca4231405dd90ae2c4a3638ca7a85e2b62f6ae30975ff3885ab60'
Verified: True
Verify signature
#!/bin/bash
set -e
# verify signature
openssl dgst -sha256 -verify rsa_pub.pem -signature sig_sha256.bin cleartext.txt
Output
$ ./verify.sh
Verified OK
Conclusion
Thanks to Leon Rman for the initial code and the idea.
I let you write the code to do the symmetrical operations: sign using OpenSSL and verify using PyKCS11.
