Quelle  test_malformed_sigs.py   Sprache: Python

from __future__ import with_statement, division

import hashlib
try:
    from hashlib import algorithms_available
except ImportError:  # pragma: no cover
    algorithms_available = [
        "md5", "sha1", "sha224", "sha256", "sha384", "sha512"]
from functools import partial
import pytest
import sys
from six import binary_type
import hypothesis.strategies as st
from hypothesis import note, assume, given, settings, example

from .keys import SigningKey
from .keys import BadSignatureError
from .util import sigencode_der, sigencode_string
from .util import sigdecode_der, sigdecode_string
from .curves import curves, NIST256p
from .der import encode_integer, encode_bitstring, encode_octet_string, \
    encode_oid, encode_sequence, encode_constructed


example_data = b"some data to sign"
"""Since the data is hashed for processing, really any string will do."""


hash_and_size = [(name, hashlib.new(name).digest_size)
                 for name in algorithms_available]
"""Pairs of hash names and their output sizes.
Needed for pairing with curves as we don't support hashes
bigger than order sizes of curves."""


keys_and_sigs = []
"""Name of the curve+hash combination, VerifyingKey and DER signature."""


# for hypothesis strategy shrinking we want smallest curves and hashes first
for curve in sorted(curves, key=lambda x: x.baselen):
    for hash_alg in [name for name, size in
                     sorted(hash_and_size, key=lambda x: x[1])
                     if 0 < size <= curve.baselen]:
        sk = SigningKey.generate(
            curve,
            hashfunc=partial(hashlib.new, hash_alg))

        keys_and_sigs.append(
            ("{0} {1}".format(curve, hash_alg),
             sk.verifying_key,
             sk.sign(example_data, sigencode=sigencode_der)))


# first make sure that the signatures can be verified
@pytest.mark.parametrize(
    "verifying_key,signature",
    [pytest.param(vk, sig, id=name) for name, vk, sig in keys_and_sigs])
def test_signatures(verifying_key, signature):
    assert verifying_key.verify(signature, example_data,
                                sigdecode=sigdecode_der)


@st.composite
def st_fuzzed_sig(draw, keys_and_sigs):
    """
    Hypothesis strategy that generates pairs of VerifyingKey and malformed
    signatures created by fuzzing of a valid signature.
    """
    name, verifying_key, old_sig = draw(st.sampled_from(keys_and_sigs))
    note("Configuration: {0}".format(name))

    sig = bytearray(old_sig)

    # decide which bytes should be removed
    to_remove = draw(st.lists(
        st.integers(min_value=0, max_value=len(sig)-1),
        unique=True))
    to_remove.sort()
    for i in reversed(to_remove):
        del sig[i]
    note("Remove bytes: {0}".format(to_remove))

    # decide which bytes of the original signature should be changed
    if sig:  # pragma: no branch
        xors = draw(st.dictionaries(
            st.integers(min_value=0, max_value=len(sig)-1),
            st.integers(min_value=1, max_value=255)))
        for i, val in xors.items():
            sig[i] ^= val
        note("xors: {0}".format(xors))

    # decide where new data should be inserted
    insert_pos = draw(st.integers(min_value=0, max_value=len(sig)))
    # NIST521p signature is about 140 bytes long, test slightly longer
    insert_data = draw(st.binary(max_size=256))

    sig = sig[:insert_pos] + insert_data + sig[insert_pos:]
    note("Inserted at position {0} bytes: {1!r}"
         .format(insert_pos, insert_data))

    sig = bytes(sig)
    # make sure that there was performed at least one mutation on the data
    assume(to_remove or xors or insert_data)
    # and that the mutations didn't cancel each-other out
    assume(sig != old_sig)

    return verifying_key, sig


params = {}
# not supported in hypothesis 2.0.0
if sys.version_info >= (2, 7):  # pragma: no branch
    from hypothesis import HealthCheck
    # deadline=5s because NIST521p are slow to verify
    params["deadline"] = 5000
    params["suppress_health_check"] = [HealthCheck.data_too_large,
                                       HealthCheck.filter_too_much,
                                       HealthCheck.too_slow]

slow_params = dict(params)
slow_params["max_examples"] = 10


@settings(**params)
@given(st_fuzzed_sig(keys_and_sigs))
def test_fuzzed_der_signatures(args):
    verifying_key, sig = args

    with pytest.raises(BadSignatureError):
        verifying_key.verify(sig, example_data, sigdecode=sigdecode_der)


@st.composite
def st_random_der_ecdsa_sig_value(draw):
    """
    Hypothesis strategy for selecting random values and encoding them
    to ECDSA-Sig-Value object::

        ECDSA-Sig-Value ::= SEQUENCE {
            r INTEGER,
            s INTEGER
        }
    """
    name, verifying_key, _ = draw(st.sampled_from(keys_and_sigs))
    note("Configuration: {0}".format(name))
    order = int(verifying_key.curve.order)

    # the encode_integer doesn't suport negative numbers, would be nice
    # to generate them too, but we have coverage for remove_integer()
    # verifying that it doesn't accept them, so meh.
    # Test all numbers around the ones that can show up (around order)
    # way smaller and slightly bigger
    r = draw(st.integers(min_value=0, max_value=order << 4) |
             st.integers(min_value=order >> 2, max_value=order+1))
    s = draw(st.integers(min_value=0, max_value=order << 4) |
             st.integers(min_value=order >> 2, max_value=order+1))

    sig = encode_sequence(encode_integer(r), encode_integer(s))

    return verifying_key, sig


@settings(**slow_params)
@given(st_random_der_ecdsa_sig_value())
def test_random_der_ecdsa_sig_value(params):
    """
    Check if random values encoded in ECDSA-Sig-Value structure are rejected
    as signature.
    """
    verifying_key, sig = params

    with pytest.raises(BadSignatureError):
        verifying_key.verify(sig, example_data, sigdecode=sigdecode_der)


def st_der_integer(*args, **kwargs):
    """
    Hypothesis strategy that returns a random positive integer as DER
    INTEGER.
    Parameters are passed to hypothesis.strategy.integer.
    """
    if "min_value" not in kwargs:  # pragma: no branch
        kwargs["min_value"] = 0
    return st.builds(encode_integer, st.integers(*args, **kwargs))


@st.composite
def st_der_bit_string(draw, *args, **kwargs):
    """
    Hypothesis strategy that returns a random DER BIT STRING.
    Parameters are passed to hypothesis.strategy.binary.
    """
    data = draw(st.binary(*args, **kwargs))
    if data:
        unused = draw(st.integers(min_value=0, max_value=7))
        data = bytearray(data)
        data[-1] &= - (2**unused)
        data = bytes(data)
    else:
        unused = 0
    return encode_bitstring(data, unused)


def st_der_octet_string(*args, **kwargs):
    """
    Hypothesis strategy that returns a random DER OCTET STRING object.
    Parameters are passed to hypothesis.strategy.binary
    """
    return st.builds(encode_octet_string, st.binary(*args, **kwargs))


def st_der_null():
    """
    Hypothesis strategy that returns DER NULL object.
    """
    return st.just(b'\x05\x00')


@st.composite
def st_der_oid(draw):
    """
    Hypothesis strategy that returns DER OBJECT IDENTIFIER objects.
    """
    first = draw(st.integers(min_value=0, max_value=2))
    if first < 2:
        second = draw(st.integers(min_value=0, max_value=39))
    else:
        second = draw(st.integers(min_value=0, max_value=2**512))
    rest = draw(st.lists(st.integers(min_value=0, max_value=2**512),
                         max_size=50))
    return encode_oid(first, second, *rest)


def st_der():
    """
    Hypothesis strategy that returns random DER structures.

    A valid DER structure is any primitive object, an octet encoding
    of a valid DER structure, sequence of valid DER objects or a constructed
    encoding of any of the above.
    """
    return st.recursive(
        st.just(b'') | st_der_integer(max_value=2**4096) |
        st_der_bit_string(max_size=1024**2) |
        st_der_octet_string(max_size=1024**2) | st_der_null() | st_der_oid(),
        lambda children:
            st.builds(lambda x: encode_octet_string(x), st.one_of(children)) |
            st.builds(lambda x: encode_bitstring(x, 0), st.one_of(children)) |
            st.builds(lambda x: encode_sequence(*x),
                      st.lists(children, max_size=200)) |
            st.builds(lambda tag, x:
                      encode_constructed(tag, x),
                      st.integers(min_value=0, max_value=0x3f),
                      st.one_of(children)),
        max_leaves=40
        )


@settings(**params)
@given(st.sampled_from(keys_and_sigs), st_der())
def test_random_der_as_signature(params, der):
    """Check if random DER structures are rejected as signature"""
    name, verifying_key, _ = params

    with pytest.raises(BadSignatureError):
        verifying_key.verify(der, example_data, sigdecode=sigdecode_der)


@settings(**params)
@given(st.sampled_from(keys_and_sigs), st.binary(max_size=1024**2))
@example(
    keys_and_sigs[0],
    encode_sequence(encode_integer(0), encode_integer(0)))
@example(
    keys_and_sigs[0],
    encode_sequence(encode_integer(1), encode_integer(1)) + b'\x00')
@example(
    keys_and_sigs[0],
    encode_sequence(*[encode_integer(1)] * 3))
def test_random_bytes_as_signature(params, der):
    """Check if random bytes are rejected as signature"""
    name, verifying_key, _ = params

    with pytest.raises(BadSignatureError):
        verifying_key.verify(der, example_data, sigdecode=sigdecode_der)


keys_and_string_sigs = [
    (name, verifying_key,
     sigencode_string(*sigdecode_der(sig, verifying_key.curve.order),
                      order=verifying_key.curve.order))
    for name, verifying_key, sig in keys_and_sigs]
"""
Name of the curve+hash combination, VerifyingKey and signature as a
byte string.
"""


@settings(**params)
@given(st_fuzzed_sig(keys_and_string_sigs))
def test_fuzzed_string_signatures(params):
    verifying_key, sig = params

    with pytest.raises(BadSignatureError):
        verifying_key.verify(sig, example_data, sigdecode=sigdecode_string)