InfiniTime/tools/mcuboot/imgtool/keys/ecdsa.py

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