158 lines
5.2 KiB
Python
158 lines
5.2 KiB
Python
"""
|
|
ECDSA key management
|
|
"""
|
|
|
|
from cryptography.hazmat.backends import default_backend
|
|
from cryptography.hazmat.primitives import serialization
|
|
from cryptography.hazmat.primitives.asymmetric import ec
|
|
from cryptography.hazmat.primitives.hashes import SHA256
|
|
|
|
from .general import KeyClass
|
|
|
|
class ECDSAUsageError(Exception):
|
|
pass
|
|
|
|
class ECDSA256P1Public(KeyClass):
|
|
def __init__(self, key):
|
|
self.key = key
|
|
|
|
def shortname(self):
|
|
return "ecdsa"
|
|
|
|
def _unsupported(self, name):
|
|
raise ECDSAUsageError("Operation {} requires private key".format(name))
|
|
|
|
def _get_public(self):
|
|
return self.key
|
|
|
|
def get_public_bytes(self):
|
|
# The key is embedded into MBUboot in "SubjectPublicKeyInfo" format
|
|
return self._get_public().public_bytes(
|
|
encoding=serialization.Encoding.DER,
|
|
format=serialization.PublicFormat.SubjectPublicKeyInfo)
|
|
|
|
def get_private_bytes(self, minimal):
|
|
self._unsupported('get_private_bytes')
|
|
|
|
def export_private(self, path, passwd=None):
|
|
self._unsupported('export_private')
|
|
|
|
def export_public(self, path):
|
|
"""Write the public key to the given file."""
|
|
pem = self._get_public().public_bytes(
|
|
encoding=serialization.Encoding.PEM,
|
|
format=serialization.PublicFormat.SubjectPublicKeyInfo)
|
|
with open(path, 'wb') as f:
|
|
f.write(pem)
|
|
|
|
def sig_type(self):
|
|
return "ECDSA256_SHA256"
|
|
|
|
def sig_tlv(self):
|
|
return "ECDSA256"
|
|
|
|
def sig_len(self):
|
|
# Early versions of MCUboot (< v1.5.0) required ECDSA
|
|
# signatures to be padded to 72 bytes. Because the DER
|
|
# encoding is done with signed integers, the size of the
|
|
# signature will vary depending on whether the high bit is set
|
|
# in each value. This padding was done in a
|
|
# not-easily-reversible way (by just adding zeros).
|
|
#
|
|
# The signing code no longer requires this padding, and newer
|
|
# versions of MCUboot don't require it. But, continue to
|
|
# return the total length so that the padding can be done if
|
|
# requested.
|
|
return 72
|
|
|
|
def verify(self, signature, payload):
|
|
# strip possible paddings added during sign
|
|
signature = signature[:signature[1] + 2]
|
|
k = self.key
|
|
if isinstance(self.key, ec.EllipticCurvePrivateKey):
|
|
k = self.key.public_key()
|
|
return k.verify(signature=signature, data=payload,
|
|
signature_algorithm=ec.ECDSA(SHA256()))
|
|
|
|
|
|
class ECDSA256P1(ECDSA256P1Public):
|
|
"""
|
|
Wrapper around an ECDSA private key.
|
|
"""
|
|
|
|
def __init__(self, key):
|
|
"""key should be an instance of EllipticCurvePrivateKey"""
|
|
self.key = key
|
|
self.pad_sig = False
|
|
|
|
@staticmethod
|
|
def generate():
|
|
pk = ec.generate_private_key(
|
|
ec.SECP256R1(),
|
|
backend=default_backend())
|
|
return ECDSA256P1(pk)
|
|
|
|
def _get_public(self):
|
|
return self.key.public_key()
|
|
|
|
def _build_minimal_ecdsa_privkey(self, der):
|
|
'''
|
|
Builds a new DER that only includes the EC private key, removing the
|
|
public key that is added as an "optional" BITSTRING.
|
|
'''
|
|
offset_PUB = 68
|
|
EXCEPTION_TEXT = "Error parsing ecdsa key. Please submit an issue!"
|
|
if der[offset_PUB] != 0xa1:
|
|
raise ECDSAUsageError(EXCEPTION_TEXT)
|
|
len_PUB = der[offset_PUB + 1]
|
|
b = bytearray(der[:-offset_PUB])
|
|
offset_SEQ = 29
|
|
if b[offset_SEQ] != 0x30:
|
|
raise ECDSAUsageError(EXCEPTION_TEXT)
|
|
b[offset_SEQ + 1] -= len_PUB
|
|
offset_OCT_STR = 27
|
|
if b[offset_OCT_STR] != 0x04:
|
|
raise ECDSAUsageError(EXCEPTION_TEXT)
|
|
b[offset_OCT_STR + 1] -= len_PUB
|
|
if b[0] != 0x30 or b[1] != 0x81:
|
|
raise ECDSAUsageError(EXCEPTION_TEXT)
|
|
b[2] -= len_PUB
|
|
return b
|
|
|
|
def get_private_bytes(self, minimal):
|
|
priv = self.key.private_bytes(
|
|
encoding=serialization.Encoding.DER,
|
|
format=serialization.PrivateFormat.PKCS8,
|
|
encryption_algorithm=serialization.NoEncryption())
|
|
if minimal:
|
|
priv = self._build_minimal_ecdsa_privkey(priv)
|
|
return priv
|
|
|
|
def export_private(self, path, passwd=None):
|
|
"""Write the private key to the given file, protecting it with the optional password."""
|
|
if passwd is None:
|
|
enc = serialization.NoEncryption()
|
|
else:
|
|
enc = serialization.BestAvailableEncryption(passwd)
|
|
pem = self.key.private_bytes(
|
|
encoding=serialization.Encoding.PEM,
|
|
format=serialization.PrivateFormat.PKCS8,
|
|
encryption_algorithm=enc)
|
|
with open(path, 'wb') as f:
|
|
f.write(pem)
|
|
|
|
def raw_sign(self, payload):
|
|
"""Return the actual signature"""
|
|
return self.key.sign(
|
|
data=payload,
|
|
signature_algorithm=ec.ECDSA(SHA256()))
|
|
|
|
def sign(self, payload):
|
|
sig = self.raw_sign(payload)
|
|
if self.pad_sig:
|
|
# To make fixed length, pad with one or two zeros.
|
|
sig += b'\000' * (self.sig_len() - len(sig))
|
|
return sig
|
|
else:
|
|
return sig
|