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EMSA_PKCS1_v_1_5_encode now works out the hash ID itself.

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This commit is contained in:
William Grant
2011-03-19 17:14:14 +11:00
parent fab1be9f2d
commit d5ffbac38a
3 changed files with 38 additions and 51 deletions
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dkim/__init__.py
+2 -14
View File
@@ -189,10 +189,6 @@ def validate_signature_fields(sig, debuglog=None):
return False
return True
# These values come from RFC 3447, section 9.2 Notes, page 43.
HASHID_SHA1 = "\x2b\x0e\x03\x02\x1a"
HASHID_SHA256 = "\x60\x86\x48\x01\x65\x03\x04\x02\x01"
def rfc822_parse(message):
"""Parse a message in RFC822 format.
@@ -321,13 +317,10 @@ def sign(message, selector, domain, privkey, identity=None, canonicalize=(Simple
h.update(x[0])
h.update(":")
h.update(x[1])
d = h.digest()
if debuglog is not None:
print >>debuglog, "sign digest:", " ".join("%02x" % ord(x) for x in d)
try:
sig2 = RSASSA_PKCS1_v1_5_sign(
d, HASHID_SHA256, pk['privateExponent'], pk['modulus'])
h, pk['privateExponent'], pk['modulus'])
except DigestTooLargeError:
raise ParameterError("digest too large for modulus")
sig_value += base64.b64encode(sig2)
@@ -392,10 +385,8 @@ def verify(message, debuglog=None, dnsfunc=dnstxt):
if sig['a'] == "rsa-sha1":
hasher = hashlib.sha1
hashid = HASHID_SHA1
elif sig['a'] == "rsa-sha256":
hasher = hashlib.sha256
hashid = HASHID_SHA256
else:
if debuglog is not None:
print >>debuglog, "Unknown signature algorithm (%s)" % sig['a']
@@ -432,13 +423,10 @@ def verify(message, debuglog=None, dnsfunc=dnstxt):
h = hasher()
hash_headers(
h, canonicalize_headers, headers, include_headers, sigheaders, sig)
d = h.digest()
if debuglog is not None:
print >>debuglog, "verify digest:", " ".join("%02x" % ord(x) for x in d)
signature = base64.b64decode(re.sub(r"\s+", "", sig['b']))
try:
return RSASSA_PKCS1_v1_5_verify(
d, hashid, signature, pk['publicExponent'], pk['modulus'])
h, signature, pk['publicExponent'], pk['modulus'])
except DigestTooLargeError:
if debuglog is not None:
print >>debuglog, "digest too large for modulus"
dkim/crypto.py
+17 -14
View File
@@ -76,6 +76,13 @@ ASN1_RSAPrivateKey = [
]
# These values come from RFC 3447, section 9.2 Notes, page 43.
HASH_ID_MAP = {
'sha1': "\x2b\x0e\x03\x02\x1a",
'sha256': "\x60\x86\x48\x01\x65\x03\x04\x02\x01",
}
class DigestTooLargeError(Exception):
"""The digest is too large to fit within the requested length."""
pass
@@ -146,21 +153,20 @@ def parse_pem_private_key(data):
return parse_private_key(pkdata)
def EMSA_PKCS1_v1_5_encode(digest, mlen, hashid):
def EMSA_PKCS1_v1_5_encode(hash, mlen):
"""Encode a digest with RFC3447 EMSA-PKCS1-v1_5.
@param digest: digest byte string to encode
@param hash: hash object to encode
@param mlen: desired message length
@param hashid: ID of the hash used to generate the digest
@return: encoded digest byte string
"""
dinfo = asn1_build(
(SEQUENCE, [
(SEQUENCE, [
(OBJECT_IDENTIFIER, hashid),
(OBJECT_IDENTIFIER, HASH_ID_MAP[hash.name]),
(NULL, None),
]),
(OCTET_STRING, digest),
(OCTET_STRING, hash.digest()),
]))
if len(dinfo)+3 > mlen:
raise DigestTooLargeError()
@@ -211,32 +217,29 @@ def perform_rsa(message, exponent, modulus, mlen):
return int2str(pow(str2int(message), exponent, modulus), mlen)
def RSASSA_PKCS1_v1_5_sign(digest, hashid, private_exponent, modulus):
def RSASSA_PKCS1_v1_5_sign(hash, private_exponent, modulus):
"""Sign a digest with RFC3447 RSASSA-PKCS1-v1_5.
@param digest: digest byte string to sign
@param hashid: ID of the hash used to generate the digest
@param hash: hash object to sign
@param private_exponent: private key exponent
@param modulus: key modulus
@return: signed digest byte string
"""
modlen = len(int2str(modulus))
encoded_digest = EMSA_PKCS1_v1_5_encode(digest, modlen, hashid)
encoded_digest = EMSA_PKCS1_v1_5_encode(hash, modlen)
return perform_rsa(encoded_digest, private_exponent, modulus, modlen)
def RSASSA_PKCS1_v1_5_verify(digest, hashid, signature, public_exponent,
modulus):
def RSASSA_PKCS1_v1_5_verify(hash, signature, public_exponent, modulus):
"""Verify a digest signed with RFC3447 RSASSA-PKCS1-v1_5.
@param digest: digest byte string to check
@param hashid: ID of the hash used to generate the digest
@param hash: hash object to check
@param signature: signed digest byte string
@param public_exponent: public key exponent
@param modulus: key modulus
@return: True if the signature is valid, False otherwise
"""
modlen = len(int2str(modulus))
encoded_digest = EMSA_PKCS1_v1_5_encode(digest, modlen, hashid)
encoded_digest = EMSA_PKCS1_v1_5_encode(hash, modlen)
signed_digest = perform_rsa(signature, public_exponent, modulus, modlen)
return encoded_digest == signed_digest
dkim/tests/test_crypto.py
+19 -23
View File
@@ -17,12 +17,9 @@
# Copyright (c) 2011 William Grant <me@williamgrant.id.au>
import base64
import hashlib
import unittest
from dkim import (
HASHID_SHA1,
HASHID_SHA256,
)
from dkim.crypto import (
DigestTooLargeError,
EMSA_PKCS1_v1_5_encode,
@@ -87,28 +84,28 @@ class TestParseKeys(unittest.TestCase):
class TestEMSA_PKCS1_v1_5(unittest.TestCase):
def test_encode_sha256(self):
digest = '0123456789abcdef0123456789abcdef'
hash = hashlib.sha256('message')
self.assertEquals(
'\x00\x01\xff\xff\xff\xff\xff\xff\xff\xff\x00'
'010\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x01\x05\x00\x04 '
+ digest,
EMSA_PKCS1_v1_5_encode(digest, 62, HASHID_SHA256))
+ hash.digest(),
EMSA_PKCS1_v1_5_encode(hash, 62))
def test_encode_sha1(self):
digest = '0123456789abcdef0123'
hash = hashlib.sha1('message')
self.assertEquals(
'\x00\x01\xff\xff\xff\xff\xff\xff\xff\xff\x00'
'0!0\x09\x06\x05\x2b\x0e\x03\x02\x1a\x05\x00\x04\x14'
+ digest,
EMSA_PKCS1_v1_5_encode(digest, 46, HASHID_SHA1))
+ hash.digest(),
EMSA_PKCS1_v1_5_encode(hash, 46))
def test_encode_forbids_too_short(self):
# PKCS#1 requires at least 8 bytes of padding, so there must be
# at least that much space.
digest = '0123456789abcdef0123'
hash = hashlib.sha1('message')
self.assertRaises(
DigestTooLargeError,
EMSA_PKCS1_v1_5_encode, digest, 45, HASHID_SHA1)
EMSA_PKCS1_v1_5_encode, hash, 45)
class TestRSA(unittest.TestCase):
@@ -136,31 +133,30 @@ class TestRSASSA(unittest.TestCase):
def setUp(self):
self.key = parse_pem_private_key(read_test_data('test.private'))
self.hash = hashlib.sha1(self.test_digest)
test_digest = '0123456789abcdef0123'
test_signature = (
'3702809f62db933a5c3d18c2c76a3470658d2e79868fac98eaaca7e87d0cdc7'
'fd091182673ed57c66531835d814ff367ffa3d764e74ca8ab301982d13eabb5'
'dbe90e5c46ea223c5d3ee835aa74aaffe06e8018affeb78b5178818cb33656c'
'ed462905bc0dc608e354f6ed3d4ec160ce9326ed227ccb0c1e5ba22098e10e6'
'c083').decode('hex')
'cc8d3647d64dd3bc12984947a27bdfbb565041fcc9db781afb4b60d29d288d8d60de'
'9e1916d6f81569c3e72af442538dd6aecb50a6de9a14565fdd679c46ff7842482e15'
'e5aa078549621b6f12ca8cd57ecfad95b18e53581e131c6c3c7cd01cb153adeb439d'
'2d6ab8b215b19be0e69ef490885004a474eb26d747a219693e8c').decode('hex')
def test_sign_and_verify(self):
signature = RSASSA_PKCS1_v1_5_sign(
self.test_digest, HASHID_SHA1, TEST_KEY_PRIVATE_EXPONENT,
TEST_KEY_MODULUS)
self.hash, TEST_KEY_PRIVATE_EXPONENT, TEST_KEY_MODULUS)
self.assertEquals(
self.test_signature, signature)
self.assertTrue(
RSASSA_PKCS1_v1_5_verify(
self.test_digest, HASHID_SHA1, signature,
TEST_KEY_PUBLIC_EXPONENT, TEST_KEY_MODULUS))
self.hash, signature, TEST_KEY_PUBLIC_EXPONENT,
TEST_KEY_MODULUS))
def test_invalid_signature(self):
self.assertFalse(
RSASSA_PKCS1_v1_5_verify(
self.test_digest, HASHID_SHA1, self.test_signature,
TEST_KEY_PUBLIC_EXPONENT, TEST_KEY_MODULUS + 1))
self.hash, self.test_signature, TEST_KEY_PUBLIC_EXPONENT,
TEST_KEY_MODULUS + 1))
def test_suite():