Merge pull request #2447 from reaperhulk/encode-decode-point
add support for encoding/decoding elliptic curve points
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 08ac109..2689273 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -16,6 +16,12 @@
:func:`~cryptography.hazmat.primitives.keywrap.aes_key_wrap` and
:func:`~cryptography.hazmat.primitives.keywrap.aes_key_unwrap`.
* Added an ``__hash__`` method to :class:`~cryptography.x509.Name`.
+* Add support for encoding and decoding elliptic curve points to a byte string
+ form using
+ :meth:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicNumbers.encode_point`
+ and
+ :meth:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicNumbers.from_encoded_point`.
+
1.0.2 - 2015-09-27
~~~~~~~~~~~~~~~~~~
diff --git a/docs/hazmat/primitives/asymmetric/ec.rst b/docs/hazmat/primitives/asymmetric/ec.rst
index 90e7371..c1619dd 100644
--- a/docs/hazmat/primitives/asymmetric/ec.rst
+++ b/docs/hazmat/primitives/asymmetric/ec.rst
@@ -122,6 +122,37 @@
:returns: A new instance of a :class:`EllipticCurvePublicKey`
provider.
+ .. method:: encode_point()
+
+ .. versionadded:: 1.1
+
+ Encodes an elliptic curve point to a byte string as described in
+ `SEC 1 v2.0`_ section 2.3.3. This method only supports uncompressed
+ points.
+
+ :return bytes: The encoded point.
+
+ .. classmethod:: from_encoded_point(curve, data)
+
+ .. versionadded:: 1.1
+
+ Decodes a byte string as described in `SEC 1 v2.0`_ section 2.3.3 and
+ returns an :class:`EllipticCurvePublicNumbers`. This method only
+ supports uncompressed points.
+
+ :param curve: An
+ :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurve`
+ instance.
+
+ :param bytes data: The serialized point byte string.
+
+ :returns: An :class:`EllipticCurvePublicNumbers` instance.
+
+ :raises ValueError: Raised on invalid point type or data length.
+
+ :raises TypeError: Raised when curve is not an
+ :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurve`.
+
Elliptic Curve Key Exchange algorithm
-------------------------------------
@@ -478,3 +509,4 @@
.. _`ECDSA`: https://en.wikipedia.org/wiki/ECDSA
.. _`EdDSA`: https://en.wikipedia.org/wiki/EdDSA
.. _`forward secrecy`: https://en.wikipedia.org/wiki/Forward_secrecy
+.. _`SEC 1 v2.0`: http://www.secg.org/sec1-v2.pdf
diff --git a/src/cryptography/hazmat/primitives/asymmetric/ec.py b/src/cryptography/hazmat/primitives/asymmetric/ec.py
index c6f8366..7782133 100644
--- a/src/cryptography/hazmat/primitives/asymmetric/ec.py
+++ b/src/cryptography/hazmat/primitives/asymmetric/ec.py
@@ -259,6 +259,31 @@
def public_key(self, backend):
return backend.load_elliptic_curve_public_numbers(self)
+ def encode_point(self):
+ # key_size is in bits. Convert to bytes and round up
+ byte_length = (self.curve.key_size + 7) // 8
+ return (
+ b'\x04' + utils.int_to_bytes(self.x, byte_length) +
+ utils.int_to_bytes(self.y, byte_length)
+ )
+
+ @classmethod
+ def from_encoded_point(cls, curve, data):
+ if not isinstance(curve, EllipticCurve):
+ raise TypeError("curve must be an EllipticCurve instance")
+
+ if data.startswith(b'\x04'):
+ # key_size is in bits. Convert to bytes and round up
+ byte_length = (curve.key_size + 7) // 8
+ if len(data) == 2 * byte_length + 1:
+ x = utils.int_from_bytes(data[1:byte_length + 1], 'big')
+ y = utils.int_from_bytes(data[byte_length + 1:], 'big')
+ return cls(x, y, curve)
+ else:
+ raise ValueError('Invalid elliptic curve point data length')
+ else:
+ raise ValueError('Unsupported elliptic curve point type')
+
curve = utils.read_only_property("_curve")
x = utils.read_only_property("_x")
y = utils.read_only_property("_y")
diff --git a/src/cryptography/utils.py b/src/cryptography/utils.py
index dac4046..dbd961f 100644
--- a/src/cryptography/utils.py
+++ b/src/cryptography/utils.py
@@ -48,9 +48,12 @@
return result
-def int_to_bytes(integer):
+def int_to_bytes(integer, length=None):
hex_string = '%x' % integer
- n = len(hex_string)
+ if length is None:
+ n = len(hex_string)
+ else:
+ n = length * 2
return binascii.unhexlify(hex_string.zfill(n + (n & 1)))
diff --git a/tests/hazmat/primitives/test_ec.py b/tests/hazmat/primitives/test_ec.py
index 4c4d5b9..5baaa3c 100644
--- a/tests/hazmat/primitives/test_ec.py
+++ b/tests/hazmat/primitives/test_ec.py
@@ -4,6 +4,7 @@
from __future__ import absolute_import, division, print_function
+import binascii
import itertools
import os
@@ -148,6 +149,72 @@
)
+def test_encode_point():
+ # secp256r1 point
+ x = int(
+ '233ea3b0027127084cd2cd336a13aeef69c598d8af61369a36454a17c6c22aec',
+ 16
+ )
+ y = int(
+ '3ea2c10a84153862be4ec82940f0543f9ba866af9751a6ee79d38460b35f442e',
+ 16
+ )
+ pn = ec.EllipticCurvePublicNumbers(x, y, ec.SECP256R1())
+ data = pn.encode_point()
+ assert data == binascii.unhexlify(
+ "04233ea3b0027127084cd2cd336a13aeef69c598d8af61369a36454a17c6c22ae"
+ "c3ea2c10a84153862be4ec82940f0543f9ba866af9751a6ee79d38460b35f442e"
+ )
+
+
+def test_from_encoded_point():
+ # secp256r1 point
+ data = binascii.unhexlify(
+ "04233ea3b0027127084cd2cd336a13aeef69c598d8af61369a36454a17c6c22ae"
+ "c3ea2c10a84153862be4ec82940f0543f9ba866af9751a6ee79d38460b35f442e"
+ )
+ pn = ec.EllipticCurvePublicNumbers.from_encoded_point(
+ ec.SECP256R1(), data
+ )
+ assert pn.x == int(
+ '233ea3b0027127084cd2cd336a13aeef69c598d8af61369a36454a17c6c22aec',
+ 16
+ )
+ assert pn.y == int(
+ '3ea2c10a84153862be4ec82940f0543f9ba866af9751a6ee79d38460b35f442e',
+ 16
+ )
+
+
+def test_from_encoded_point_invalid_length():
+ bad_data = binascii.unhexlify(
+ "04233ea3b0027127084cd2cd336a13aeef69c598d8af61369a36454a17c6c22ae"
+ "c3ea2c10a84153862be4ec82940f0543f9ba866af9751a6ee79d38460"
+ )
+ with pytest.raises(ValueError):
+ ec.EllipticCurvePublicNumbers.from_encoded_point(
+ ec.SECP384R1(), bad_data
+ )
+
+
+def test_from_encoded_point_unsupported_point_type():
+ # set to point type 2.
+ unsupported_type = binascii.unhexlify(
+ "02233ea3b0027127084cd2cd336a13aeef69c598d8af61369a36454a17c6c22a"
+ )
+ with pytest.raises(ValueError):
+ ec.EllipticCurvePublicNumbers.from_encoded_point(
+ ec.SECP256R1(), unsupported_type
+ )
+
+
+def test_from_encoded_point_not_a_curve():
+ with pytest.raises(TypeError):
+ ec.EllipticCurvePublicNumbers.from_encoded_point(
+ "notacurve", b"\x04data"
+ )
+
+
@pytest.mark.requires_backend_interface(interface=EllipticCurveBackend)
class TestECWithNumbers(object):
@pytest.mark.parametrize(