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import base64
import binascii
import struct
try:
from cryptography.hazmat.primitives.asymmetric.utils import (
decode_dss_signature,
encode_dss_signature,
)
except ImportError:
pass
def force_bytes(value):
if isinstance(value, str):
return value.encode("utf-8")
elif isinstance(value, bytes):
return value
else:
raise TypeError("Expected a string value")
def base64url_decode(input):
if isinstance(input, str):
input = input.encode("ascii")
rem = len(input) % 4
if rem > 0:
input += b"=" * (4 - rem)
return base64.urlsafe_b64decode(input)
def base64url_encode(input):
return base64.urlsafe_b64encode(input).replace(b"=", b"")
def to_base64url_uint(val):
if val < 0:
raise ValueError("Must be a positive integer")
int_bytes = bytes_from_int(val)
if len(int_bytes) == 0:
int_bytes = b"\x00"
return base64url_encode(int_bytes)
def from_base64url_uint(val):
if isinstance(val, str):
val = val.encode("ascii")
data = base64url_decode(val)
buf = struct.unpack("%sB" % len(data), data)
return int("".join(["%02x" % byte for byte in buf]), 16)
def number_to_bytes(num, num_bytes):
padded_hex = "%0*x" % (2 * num_bytes, num)
big_endian = binascii.a2b_hex(padded_hex.encode("ascii"))
return big_endian
def bytes_to_number(string):
return int(binascii.b2a_hex(string), 16)
def bytes_from_int(val):
remaining = val
byte_length = 0
while remaining != 0:
remaining = remaining >> 8
byte_length += 1
return val.to_bytes(byte_length, "big", signed=False)
def der_to_raw_signature(der_sig, curve):
num_bits = curve.key_size
num_bytes = (num_bits + 7) // 8
r, s = decode_dss_signature(der_sig)
return number_to_bytes(r, num_bytes) + number_to_bytes(s, num_bytes)
def raw_to_der_signature(raw_sig, curve):
num_bits = curve.key_size
num_bytes = (num_bits + 7) // 8
if len(raw_sig) != 2 * num_bytes:
raise ValueError("Invalid signature")
r = bytes_to_number(raw_sig[:num_bytes])
s = bytes_to_number(raw_sig[num_bytes:])
return encode_dss_signature(r, s)
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