Add PKCS11-based HSM interface #229

lukpueh · 2020-04-06T17:28:34Z

Fixes issue #:
Supersedes #170 and #221 (big kudos to @tanishqjasoria for excellent groundwork!)
~~Bases on / incorporates #228 (needs rebase here after #228 is merged)~~ (rebased on #228)

Description of the changes being introduced by the pull request:

Add public interface to:

list available HSMs (get_hsms), and
keys on a given HSM (get_keys_on_hsm),
sign data with a private key on the HSM, exporting the signature into a securesystemslib-like format (create_signature), and to
export a key from the HSM using a sslib-like format (export_pubkey) to be used for signature verification.

Signature verification can be performed with the existing securesystemslib.keys.verify_signature function.

Currently the HSM interface supports ecdsa keys and the "ecdsa-sha2-nistp256" and "ecdsa-sha2-nistp384" signature schemes.

Any interaction with the HSM interface require a one-time call to load_pkcs11_lib passing it the path to a PKCS11 dynamic library.

The commit also adds a basic test loop (sign + export key -> verify) using SoftHSM, as well interface tests that check that the public functions error gracefully if optional dependencies are not installed.

TODO:

error handling
- PKCS11 seems brittle, make sure that there are no state problems (e.g. openSession on a slot requires prior call to et slots, etc.) and we always get back the values we expect, i.e. handle hsm return invalid / incomplete data (e.g. on getAttributeValue), and fail gracefully if not
  HINT: check CKR_<RETURN VALUE TYPE> constants
- revise error messages and exception taxonomy
- Add HSM_INFO_SCHEMA, HSM_KEY_INFO_SCHEMA, HSM_KEY_ID_SCHEMA and check_match on them.
docs
- flesh out function docstrings and add code comments
- add links to PKCS11 specs
- add installation and usage docs, e.g. replace test_hsm.TestECDSAOnLUKPUEHsYubiKey with some instructions for YubiKey in README.md

Please verify and check that the pull request fulfils the following
requirements:

The code follows the Code Style Guidelines
Tests have been added for the bug fix or new feature
Docs have been added for the bug fix or new feature

lukpueh · 2020-04-06T18:26:25Z

Snippets to test with YubiKey on PIV slot

# Create key and sign it (the latter is important!)
yubico-piv-tool -a generate -s 9c -A ECCP256 -k -o public.pem
yubico-piv-tool -a verify-pin -a selfsign -s 9c -i public.pem -S /CN=a.b.c/OU=abc/O=b.c/ -o cert.pem
yubico-piv-tool -k -a import-certificate -s 9c -i cert.pem

import securesystemslib.hsm
import securesystemslib.keys

sslib_key_id = \
    "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"
scheme = securesystemslib.hsm.ECDSA_SHA2_NISTP256
data = b"data to be signed"

user_pin = "USER PIN" # TODO: Replace
pkcs11_so_path = "/path/to/pkcs11/shared/object/or/dynamic/lib" # TODO: replace
# E.g. /usr/local/Cellar/yubico-piv-tool/2.0.0/lib/libykcs11.dylib when
# installing with brew

# Init PKCS11
securesystemslib.hsm.load_pkcs11_lib(pkcs11_so_path)

# Get YubiKey assuming it is on the 1st slot
hsm_info = securesystemslib.hsm.get_hsms().pop()

key_infos = securesystemslib.hsm.get_keys_on_hsm(hsm_info)

# Grab keyid by label (NOTE: I promise better tooling ;)
hsm_key_id = [key_info["key_id"] for key_info in key_infos if key_info["label"] == "Public key for Digital Signature"].pop()

# Export public key
pub = securesystemslib.hsm.export_pubkey(
    hsm_info, hsm_key_id, scheme, sslib_key_id)

# Create signature
sig = securesystemslib.hsm.create_signature(
    hsm_info, hsm_key_id, user_pin, data, scheme, sslib_key_id)

# Verify signature
sig_valid = securesystemslib.keys.verify_signature(pub, sig, data)

assert sig_valid == True

- pykcs11 to communicate with HSM (requires native swig and pkcs11 libraries, kept optional to allow pure Python sslib install) - asn1crypto to decode ecdsa public keys exported from HSM - unrelated: update enum34 TODO: Add installation docs (native dependencies, extras install)

Add public interface to - list available HSMs (get_hsms), and - keys on a given HSM (get_keys_on_hsm), - sign data with a private key on the HSM, exporting the signature into a securesystemslib-liek format (create_signature), and to - export a key from the HSM using a sslib-like format (export_pubkey) to be used for signature verification. Signature verification can be performed with the existing securesystemslib.keys.verify_signature() function. Currently the HSM interface supports ecdsa keys and the "ecdsa-sha2-nistp256" and "ecdsa-sha2-nistp384" signature schemes. The commit also adds a basic test loop (sign + export key -> verify) using SoftHSM, as well interface tests that check that the public functions error gracefully if optional dependencies are not installed. TODO: - error handling - PKCS11 seems brittle, make sure that there are no state problems (e.g. openSession on a slot requires prior call to get slots, etc.) and we always get back the values we expect, i.e. handle hsm return invalid / incomplete data (e.g. on getAttributeValue), and fail gracefully if not HINT: check `CKR_<RETURN VALUE TYPE>` constants - revise error messages and exception taxonomy - Add HSM_INFO_SCHEMA and HSM_INFO_SCHEMA, HSM_KEY_INFO_SCHEMA, HSM_KEY_ID_SCHEMA and check_match on them. - docs - flesh out function docstrings and add code comments - add links to PKCS11 specs - add installation and usage docs, e.g. replace test_hsm.TestECDSAOnLUKPUEHsYubiKey with some instructions for YubiKey in README.md - testing - check coverage - trigger edge cases (see error handling above) Co-authored-by: Tanishq Jasoria <jasoriatanishq@gmail.com>

jku · 2022-10-21T15:42:03Z

slowly moving towards actually testing something... Documenting on the way: this is likely not useful to anyone else:

I think this also generates key and signs a cert (I don't have a management key set and yubico-piv-tool does not seem to like that -- this might be a deprecated feature that I should not be using but 🤷 ):
```
ykman piv keys generate --algorithm ECCP256 9c pubkey.pem
ykman piv certificates generate --subject "yubico" 9c pubkey.pem
```
I just noticed the step "manually dlopen a library" and ...
securesystemslib.hsm.load_pkcs11_lib("/usr/local/Cellar/yubico-piv-tool/2.0.0/lib/libykcs11.dylib")
Is this really the best we can do -- it feels barbaric?
On linux "/usr/lib/x86_64-linux-gnu/opensc-pkcs11.so" seems to work
The label on my HSM key is not what's on your script (maybe because different tool created it)
create_signature() fails with PyKCS11.PyKCS11Error: CKR_USER_NOT_LOGGED_IN -- the pin is correct as I get a different error if I use the wrong pin... I wonder if my key is really in working order

jku · 2022-10-24T08:44:41Z

Continuing documenting my attempt at testing:

Yubico does not document which tool should be used for this but I've now switched to yubico-piv-tool instead of ykman to reproduce Lukas's steps, I have reset the "management key" and...

~/src/securesystemslib$ yubico-piv-tool -a generate -s 9c -A ECCP256 -k -o public.pem
Enter management key: 
Successfully generated a new private key.
~/src/securesystemslib$ yubico-piv-tool -a verify-pin -a selfsign -s 9c -i public.pem -S /CN=a.b.c/OU=abc/O=b.c/ -o cert.pem
Enter PIN: 
Successfully verified PIN.
Failed signing certificate.

Even full verbosity gives nothing useful. This UX is worse than pgp AND it also doesn't work. I am not sure if I can do anything more at the moment

jku · 2022-11-07T11:28:10Z

So I was finally able to run the snippet succesfully (thanks lukas):

yubico-piv-tool is 2.2.0 (on debian) apparently creates broken keys that fail self-sign: installing to 2.3.0 and creating th key there helped
the code does not work with opensc-pkcs11.so: signing fails with CKR_USER_NOT_LOGGED_IN. It does owrk with the yubico module. I am able to use pkcs11-tool to sign and verify with either module

So, using yubico-piv-tool 2.3.0 and Yubicos libykcs11.so as the pkcs library, the example code worked.

The first issue pivtool 2.2.0 being broken does not need fixing (or can be addressed with a note in docs)
the pkcs module issue maybe should be somehow mitigated: I don't understand who is supposed to choose the PKCS11 module and why?

jku

A few years later, some review comments (I'm mostly looking at this from the POV of the Signer interface and #447):

I think we should not expose all of this as a new module -- especially things like get_keys_on_hsm(), get_hsms() seem like things that should not be public API here

HSMSigner on the other hand sounds like a reasonable thing: The API would include

key and device ids as constructor arguments (optional if PyKCS supports that)
PKCS module loaded using environment variable (optional if there are reasonable defaults for some systems)
PIN as constructor variable

This would be compatible with #447 with a URI like hsm:device/0/slot/c9 or hsm:?slot=c9&device=0, and pin getting requested with secrets_handler()

After implementing HSMSigner, the remaining public functionality in this PR would then be export_pubkey(). Interestingly this same issue comes up with KMS keys... Maybe public key export could actually be a method on the Signer as well: not all implementations would support it but some could?

Another thing that comes up with KMS keys as well is the need to prehash the payload. We should add that support somewhere -- figuring out the algorithm from the public key is currently very annoying. Can we have Key.get_payload_hash_algorithm()?

Left also some code comments -- they may be obsolete so feel free to disregard

jku · 2022-11-07T11:58:58Z

securesystemslib/hsm.py

+     # If path is not passed PyKCS11 consults the PYKCS11LIB env var
+    if path is None:
+      PKCS11.load()
+
+    else:
+      securesystemslib.formats.PATH_SCHEMA.check_match(path)
+      PKCS11.load(path)


why not just PKCS11.load(path)? docs seem to imply that None is perfectly vaid here

jku · 2022-11-07T12:00:29Z

securesystemslib/hsm.py

+  except PyKCS11.PyKCS11Error as e:
+    PKCS11_DYN_LIB = False
+    raise


If you set PKCS11_DYN_LIB = False before the try block, this except is not needed

jku · 2022-11-07T12:13:50Z

securesystemslib/hsm.py

+import binascii
+
+if not six.PY2:
+  import asn1crypto.keys


asn1crypto is now a dependency for all securesystemslib users?

jku · 2022-11-07T13:21:08Z

setup.py

@@ -100,10 +100,11 @@
    'Topic :: Software Development'
  ],
  install_requires = ['six>=1.11.0', 'subprocess32; python_version < "3"',
-      'python-dateutil>=2.8.0'],
+      'python-dateutil>=2.8.0', 'asn1crypto; python_version > "3"'],


I mentioned this elsewhere but this seems wrong: it should be only needed for "pkcs11" extra, right?

lukpueh · 2022-12-01T13:50:02Z

Superseded by #472, which adds the relevant parts of this implementation to the new Signer/Key API.

This was referenced Apr 6, 2020

External Signing using CCID/PIV interface. #170

Closed

External Signing using PIV interface. #221

Closed

lukpueh and others added 2 commits April 9, 2020 10:11

lukpueh force-pushed the pkcs11-hsm-interface branch from 73cce96 to 2e20c56 Compare April 9, 2020 08:12

joshuagl mentioned this pull request May 15, 2020

Refactor format_metadata_to_key #227

Merged

3 tasks

This was referenced Jul 7, 2020

External Signing API, or CCID/PIV Support theupdateframework/python-tuf#864

Closed

Support hardware security modules or signing metadata externally theupdateframework/python-tuf#569

Closed

lukpueh mentioned this pull request Aug 3, 2020

Hardware Security Module (HSM) Support in-toto/in-toto-golang#61

Open

joshuagl mentioned this pull request Nov 26, 2020

Enable signing and verifying using keys stored in Hashicorp Vault #307

Closed

This was referenced Dec 8, 2020

Revise public key metadata format #308

Closed

Revise stand-alone on-disk key format #309

Closed

lukpueh mentioned this pull request Mar 21, 2022

Support HSM signing theupdateframework/python-tuf#1912

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jku reviewed Nov 7, 2022

View reviewed changes

lukpueh mentioned this pull request Dec 1, 2022

Add HSMSigner #472

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lukpueh closed this Dec 1, 2022

jku mentioned this pull request Jan 12, 2023

docs: Add short HOWTO doc on Yubikey usage #494

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Add PKCS11-based HSM interface #229

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Add PKCS11-based HSM interface #229

Add PKCS11-based HSM interface #229

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