253 lines
11 KiB
Python
253 lines
11 KiB
Python
import binascii
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import ecdsa
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import der
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from curves import NIST192p, find_curve
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from util import string_to_number, number_to_string, randrange
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from util import sigencode_string, sigdecode_string
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from util import oid_ecPublicKey, encoded_oid_ecPublicKey
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from hashlib import sha1
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class BadSignatureError(Exception):
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pass
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class BadDigestError(Exception):
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pass
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class VerifyingKey:
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def __init__(self, _error__please_use_generate=None):
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if not _error__please_use_generate:
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raise TypeError("Please use SigningKey.generate() to construct me")
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@classmethod
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def from_public_point(klass, point, curve=NIST192p, hashfunc=sha1):
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self = klass(_error__please_use_generate=True)
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self.curve = curve
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self.default_hashfunc = hashfunc
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self.pubkey = ecdsa.Public_key(curve.generator, point)
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self.pubkey.order = curve.order
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return self
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@classmethod
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def from_string(klass, string, curve=NIST192p, hashfunc=sha1):
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order = curve.order
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assert len(string) == curve.verifying_key_length, \
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(len(string), curve.verifying_key_length)
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xs = string[:curve.baselen]
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ys = string[curve.baselen:]
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assert len(xs) == curve.baselen, (len(xs), curve.baselen)
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assert len(ys) == curve.baselen, (len(ys), curve.baselen)
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x = string_to_number(xs)
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y = string_to_number(ys)
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assert ecdsa.point_is_valid(curve.generator, x, y)
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import ellipticcurve
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point = ellipticcurve.Point(curve.curve, x, y, order)
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return klass.from_public_point(point, curve, hashfunc)
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@classmethod
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def from_pem(klass, string):
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return klass.from_der(der.unpem(string))
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@classmethod
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def from_der(klass, string):
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# [[oid_ecPublicKey,oid_curve], point_str_bitstring]
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s1,empty = der.remove_sequence(string)
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if empty != "":
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raise der.UnexpectedDER("trailing junk after DER pubkey: %s" %
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binascii.hexlify(empty))
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s2,point_str_bitstring = der.remove_sequence(s1)
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# s2 = oid_ecPublicKey,oid_curve
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oid_pk, rest = der.remove_object(s2)
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oid_curve, empty = der.remove_object(rest)
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if empty != "":
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raise der.UnexpectedDER("trailing junk after DER pubkey objects: %s" %
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binascii.hexlify(empty))
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assert oid_pk == oid_ecPublicKey, (oid_pk, oid_ecPublicKey)
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curve = find_curve(oid_curve)
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point_str, empty = der.remove_bitstring(point_str_bitstring)
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if empty != "":
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raise der.UnexpectedDER("trailing junk after pubkey pointstring: %s" %
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binascii.hexlify(empty))
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assert point_str.startswith("\x00\x04")
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return klass.from_string(point_str[2:], curve)
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def to_string(self):
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# VerifyingKey.from_string(vk.to_string()) == vk as long as the
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# curves are the same: the curve itself is not included in the
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# serialized form
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order = self.pubkey.order
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x_str = number_to_string(self.pubkey.point.x(), order)
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y_str = number_to_string(self.pubkey.point.y(), order)
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return x_str + y_str
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def to_pem(self):
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return der.topem(self.to_der(), "PUBLIC KEY")
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def to_der(self):
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order = self.pubkey.order
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x_str = number_to_string(self.pubkey.point.x(), order)
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y_str = number_to_string(self.pubkey.point.y(), order)
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point_str = "\x00\x04" + x_str + y_str
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return der.encode_sequence(der.encode_sequence(encoded_oid_ecPublicKey,
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self.curve.encoded_oid),
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der.encode_bitstring(point_str))
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def verify(self, signature, data, hashfunc=None, sigdecode=sigdecode_string):
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hashfunc = hashfunc or self.default_hashfunc
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digest = hashfunc(data).digest()
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return self.verify_digest(signature, digest, sigdecode)
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def verify_digest(self, signature, digest, sigdecode=sigdecode_string):
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if len(digest) > self.curve.baselen:
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raise BadDigestError("this curve (%s) is too short "
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"for your digest (%d)" % (self.curve.name,
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8*len(digest)))
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number = string_to_number(digest)
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r, s = sigdecode(signature, self.pubkey.order)
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sig = ecdsa.Signature(r, s)
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if self.pubkey.verifies(number, sig):
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return True
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raise BadSignatureError
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class SigningKey:
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def __init__(self, _error__please_use_generate=None):
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if not _error__please_use_generate:
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raise TypeError("Please use SigningKey.generate() to construct me")
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@classmethod
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def generate(klass, curve=NIST192p, entropy=None, hashfunc=sha1):
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secexp = randrange(curve.order, entropy)
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return klass.from_secret_exponent(secexp, curve, hashfunc)
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# to create a signing key from a short (arbitrary-length) seed, convert
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# that seed into an integer with something like
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# secexp=util.randrange_from_seed__X(seed, curve.order), and then pass
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# that integer into SigningKey.from_secret_exponent(secexp, curve)
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@classmethod
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def from_secret_exponent(klass, secexp, curve=NIST192p, hashfunc=sha1):
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self = klass(_error__please_use_generate=True)
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self.curve = curve
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self.default_hashfunc = hashfunc
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self.baselen = curve.baselen
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n = curve.order
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assert 1 <= secexp < n
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pubkey_point = curve.generator*secexp
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pubkey = ecdsa.Public_key(curve.generator, pubkey_point)
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pubkey.order = n
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self.verifying_key = VerifyingKey.from_public_point(pubkey_point, curve,
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hashfunc)
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self.privkey = ecdsa.Private_key(pubkey, secexp)
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self.privkey.order = n
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return self
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@classmethod
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def from_string(klass, string, curve=NIST192p, hashfunc=sha1):
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assert len(string) == curve.baselen, (len(string), curve.baselen)
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secexp = string_to_number(string)
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return klass.from_secret_exponent(secexp, curve, hashfunc)
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@classmethod
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def from_pem(klass, string, hashfunc=sha1):
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# the privkey pem file has two sections: "EC PARAMETERS" and "EC
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# PRIVATE KEY". The first is redundant.
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privkey_pem = string[string.index("-----BEGIN EC PRIVATE KEY-----"):]
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return klass.from_der(der.unpem(privkey_pem), hashfunc)
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@classmethod
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def from_der(klass, string, hashfunc=sha1):
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# SEQ([int(1), octetstring(privkey),cont[0], oid(secp224r1),
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# cont[1],bitstring])
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s, empty = der.remove_sequence(string)
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if empty != "":
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raise der.UnexpectedDER("trailing junk after DER privkey: %s" %
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binascii.hexlify(empty))
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one, s = der.remove_integer(s)
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if one != 1:
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raise der.UnexpectedDER("expected '1' at start of DER privkey,"
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" got %d" % one)
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privkey_str, s = der.remove_octet_string(s)
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tag, curve_oid_str, s = der.remove_constructed(s)
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if tag != 0:
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raise der.UnexpectedDER("expected tag 0 in DER privkey,"
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" got %d" % tag)
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curve_oid, empty = der.remove_object(curve_oid_str)
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if empty != "":
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raise der.UnexpectedDER("trailing junk after DER privkey "
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"curve_oid: %s" % binascii.hexlify(empty))
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curve = find_curve(curve_oid)
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# we don't actually care about the following fields
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#
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#tag, pubkey_bitstring, s = der.remove_constructed(s)
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#if tag != 1:
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# raise der.UnexpectedDER("expected tag 1 in DER privkey, got %d"
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# % tag)
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#pubkey_str = der.remove_bitstring(pubkey_bitstring)
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#if empty != "":
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# raise der.UnexpectedDER("trailing junk after DER privkey "
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# "pubkeystr: %s" % binascii.hexlify(empty))
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# our from_string method likes fixed-length privkey strings
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if len(privkey_str) < curve.baselen:
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privkey_str = "\x00"*(curve.baselen-len(privkey_str)) + privkey_str
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return klass.from_string(privkey_str, curve, hashfunc)
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def to_string(self):
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secexp = self.privkey.secret_multiplier
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s = number_to_string(secexp, self.privkey.order)
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return s
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def to_pem(self):
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# TODO: "BEGIN ECPARAMETERS"
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return der.topem(self.to_der(), "EC PRIVATE KEY")
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def to_der(self):
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# SEQ([int(1), octetstring(privkey),cont[0], oid(secp224r1),
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# cont[1],bitstring])
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encoded_vk = "\x00\x04" + self.get_verifying_key().to_string()
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return der.encode_sequence(der.encode_integer(1),
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der.encode_octet_string(self.to_string()),
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der.encode_constructed(0, self.curve.encoded_oid),
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der.encode_constructed(1, der.encode_bitstring(encoded_vk)),
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)
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def get_verifying_key(self):
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return self.verifying_key
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def sign(self, data, entropy=None, hashfunc=None, sigencode=sigencode_string):
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"""
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hashfunc= should behave like hashlib.sha1 . The output length of the
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hash (in bytes) must not be longer than the length of the curve order
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(rounded up to the nearest byte), so using SHA256 with nist256p is
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ok, but SHA256 with nist192p is not. (In the 2**-96ish unlikely event
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of a hash output larger than the curve order, the hash will
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effectively be wrapped mod n).
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Use hashfunc=hashlib.sha1 to match openssl's -ecdsa-with-SHA1 mode,
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or hashfunc=hashlib.sha256 for openssl-1.0.0's -ecdsa-with-SHA256.
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"""
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hashfunc = hashfunc or self.default_hashfunc
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h = hashfunc(data).digest()
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return self.sign_digest(h, entropy, sigencode)
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def sign_digest(self, digest, entropy=None, sigencode=sigencode_string):
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if len(digest) > self.curve.baselen:
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raise BadDigestError("this curve (%s) is too short "
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"for your digest (%d)" % (self.curve.name,
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8*len(digest)))
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number = string_to_number(digest)
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r, s = self.sign_number(number, entropy)
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return sigencode(r, s, self.privkey.order)
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def sign_number(self, number, entropy=None):
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# returns a pair of numbers
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order = self.privkey.order
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# privkey.sign() may raise RuntimeError in the amazingly unlikely
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# (2**-192) event that r=0 or s=0, because that would leak the key.
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# We could re-try with a different 'k', but we couldn't test that
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# code, so I choose to allow the signature to fail instead.
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k = randrange(order, entropy)
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assert 1 <= k < order
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sig = self.privkey.sign(number, k)
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return sig.r, sig.s
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