mirror of
https://github.com/cuberite/polarssl.git
synced 2025-10-30 11:11:12 -04:00
New python module to encode a PSA key for storage
Construct an object given the attributes and material for a PSA crypto key and get the Mbed TLS storage representation. The code to generate the storage representation was written based on the specification in docs/architecture/mbed-crypto-storage-specification.md, without looking at the code. The data in the unit tests is from the AES-128 format_storage_data_check test case in test_suite_psa_crypto_persistent_key.data, tweaked manually. This commit creates a basic framework for using symbolic values for attributes, but does not yet implement obtaining the corresponding numerical values from an external source. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
parent
00d37d0026
commit
e00944807c
184
scripts/mbedtls_dev/psa_storage.py
Normal file
184
scripts/mbedtls_dev/psa_storage.py
Normal file
@ -0,0 +1,184 @@
|
||||
"""Knowledge about the PSA key store as implemented in Mbed TLS.
|
||||
"""
|
||||
|
||||
# Copyright The Mbed TLS Contributors
|
||||
# SPDX-License-Identifier: Apache-2.0
|
||||
#
|
||||
# Licensed under the Apache License, Version 2.0 (the "License"); you may
|
||||
# not use this file except in compliance with the License.
|
||||
# You may obtain a copy of the License at
|
||||
#
|
||||
# http://www.apache.org/licenses/LICENSE-2.0
|
||||
#
|
||||
# Unless required by applicable law or agreed to in writing, software
|
||||
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
|
||||
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
||||
# See the License for the specific language governing permissions and
|
||||
# limitations under the License.
|
||||
|
||||
import re
|
||||
import struct
|
||||
from typing import Optional, Union
|
||||
import unittest
|
||||
|
||||
|
||||
class Expr:
|
||||
"""Representation of a C expression with a known or knowable numerical value."""
|
||||
def __init__(self, content: Union[int, str]):
|
||||
if isinstance(content, int):
|
||||
digits = 8 if content > 0xffff else 4
|
||||
self.string = '{0:#0{1}x}'.format(content, digits + 2)
|
||||
self.value_if_known = content #type: Optional[int]
|
||||
else:
|
||||
self.string = content
|
||||
self.value_if_known = None
|
||||
|
||||
value_cache = {
|
||||
# Hard-coded for initial testing
|
||||
'PSA_KEY_LIFETIME_PERSISTENT': 0x00000001,
|
||||
'PSA_KEY_TYPE_RAW_DATA': 0x1001,
|
||||
}
|
||||
|
||||
def update_cache(self) -> None:
|
||||
pass #not implemented yet
|
||||
|
||||
@staticmethod
|
||||
def normalize(string: str) -> str:
|
||||
"""Put the given C expression in a canonical form.
|
||||
|
||||
This function is only intended to give correct results for the
|
||||
relatively simple kind of C expression typically used with this
|
||||
module.
|
||||
"""
|
||||
return re.sub(r'\s+', r'', string)
|
||||
|
||||
def value(self) -> int:
|
||||
"""Return the numerical value of the expression."""
|
||||
if self.value_if_known is None:
|
||||
if re.match(r'([0-9]+|0x[0-9a-f]+)\Z', self.string, re.I):
|
||||
return int(self.string, 0)
|
||||
normalized = self.normalize(self.string)
|
||||
if normalized not in self.value_cache:
|
||||
self.update_cache()
|
||||
self.value_if_known = self.value_cache[normalized]
|
||||
return self.value_if_known
|
||||
|
||||
Exprable = Union[str, int, Expr]
|
||||
"""Something that can be converted to a C expression with a known numerical value."""
|
||||
|
||||
def as_expr(thing: Exprable) -> Expr:
|
||||
"""Return an `Expr` object for `thing`.
|
||||
|
||||
If `thing` is already an `Expr` object, return it. Otherwise build a new
|
||||
`Expr` object from `thing`. `thing` can be an integer or a string that
|
||||
contains a C expression.
|
||||
"""
|
||||
if isinstance(thing, Expr):
|
||||
return thing
|
||||
else:
|
||||
return Expr(thing)
|
||||
|
||||
|
||||
class Key:
|
||||
"""Representation of a PSA crypto key object and its storage encoding.
|
||||
"""
|
||||
|
||||
LATEST_VERSION = 0
|
||||
"""The latest version of the storage format."""
|
||||
|
||||
def __init__(self, *,
|
||||
version: Optional[int] = None,
|
||||
id: Optional[int] = None, #pylint: disable=redefined-builtin
|
||||
lifetime: Exprable = 'PSA_KEY_LIFETIME_PERSISTENT',
|
||||
type: Exprable, #pylint: disable=redefined-builtin
|
||||
bits: int,
|
||||
usage: Exprable, alg: Exprable, alg2: Exprable,
|
||||
material: bytes #pylint: disable=used-before-assignment
|
||||
) -> None:
|
||||
self.version = self.LATEST_VERSION if version is None else version
|
||||
self.id = id #pylint: disable=invalid-name #type: Optional[int]
|
||||
self.lifetime = as_expr(lifetime) #type: Expr
|
||||
self.type = as_expr(type) #type: Expr
|
||||
self.bits = bits #type: int
|
||||
self.usage = as_expr(usage) #type: Expr
|
||||
self.alg = as_expr(alg) #type: Expr
|
||||
self.alg2 = as_expr(alg2) #type: Expr
|
||||
self.material = material #type: bytes
|
||||
|
||||
MAGIC = b'PSA\000KEY\000'
|
||||
|
||||
@staticmethod
|
||||
def pack(
|
||||
fmt: str,
|
||||
*args: Union[int, Expr]
|
||||
) -> bytes: #pylint: disable=used-before-assignment
|
||||
"""Pack the given arguments into a byte string according to the given format.
|
||||
|
||||
This function is similar to `struct.pack`, but with the following differences:
|
||||
* All integer values are encoded with standard sizes and in
|
||||
little-endian representation. `fmt` must not include an endianness
|
||||
prefix.
|
||||
* Arguments can be `Expr` objects instead of integers.
|
||||
* Only integer-valued elements are supported.
|
||||
"""
|
||||
return struct.pack('<' + fmt, # little-endian, standard sizes
|
||||
*[arg.value() if isinstance(arg, Expr) else arg
|
||||
for arg in args])
|
||||
|
||||
def bytes(self) -> bytes:
|
||||
"""Return the representation of the key in storage as a byte array.
|
||||
|
||||
This is the content of the PSA storage file. When PSA storage is
|
||||
implemented over stdio files, this does not include any wrapping made
|
||||
by the PSA-storage-over-stdio-file implementation.
|
||||
"""
|
||||
header = self.MAGIC + self.pack('L', self.version)
|
||||
if self.version == 0:
|
||||
attributes = self.pack('LHHLLL',
|
||||
self.lifetime, self.type, self.bits,
|
||||
self.usage, self.alg, self.alg2)
|
||||
material = self.pack('L', len(self.material)) + self.material
|
||||
else:
|
||||
raise NotImplementedError
|
||||
return header + attributes + material
|
||||
|
||||
def hex(self) -> str:
|
||||
"""Return the representation of the key as a hexadecimal string.
|
||||
|
||||
This is the hexadecimal representation of `self.bytes`.
|
||||
"""
|
||||
return self.bytes().hex()
|
||||
|
||||
|
||||
class TestKey(unittest.TestCase):
|
||||
# pylint: disable=line-too-long
|
||||
"""A few smoke tests for the functionality of the `Key` class."""
|
||||
|
||||
def test_numerical(self):
|
||||
key = Key(version=0,
|
||||
id=1, lifetime=0x00000001,
|
||||
type=0x2400, bits=128,
|
||||
usage=0x00000300, alg=0x05500200, alg2=0x04c01000,
|
||||
material=b'@ABCDEFGHIJKLMNO')
|
||||
expected_hex = '505341004b45590000000000010000000024800000030000000250050010c00410000000404142434445464748494a4b4c4d4e4f'
|
||||
self.assertEqual(key.bytes(), bytes.fromhex(expected_hex))
|
||||
self.assertEqual(key.hex(), expected_hex)
|
||||
|
||||
def test_names(self):
|
||||
length = 0xfff8 // 8 # PSA_MAX_KEY_BITS in bytes
|
||||
key = Key(version=0,
|
||||
id=1, lifetime='PSA_KEY_LIFETIME_PERSISTENT',
|
||||
type='PSA_KEY_TYPE_RAW_DATA', bits=length*8,
|
||||
usage=0, alg=0, alg2=0,
|
||||
material=b'\x00' * length)
|
||||
expected_hex = '505341004b45590000000000010000000110f8ff000000000000000000000000ff1f0000' + '00' * length
|
||||
self.assertEqual(key.bytes(), bytes.fromhex(expected_hex))
|
||||
self.assertEqual(key.hex(), expected_hex)
|
||||
|
||||
def test_defaults(self):
|
||||
key = Key(type=0x1001, bits=8,
|
||||
usage=0, alg=0, alg2=0,
|
||||
material=b'\x2a')
|
||||
expected_hex = '505341004b455900000000000100000001100800000000000000000000000000010000002a'
|
||||
self.assertEqual(key.bytes(), bytes.fromhex(expected_hex))
|
||||
self.assertEqual(key.hex(), expected_hex)
|
||||
Loading…
x
Reference in New Issue
Block a user