William Grant
161 lines
4.2 KiB
Python
161 lines
4.2 KiB
Python
# This software is provided 'as-is', without any express or implied
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# warranty. In no event will the author be held liable for any damages
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# arising from the use of this software.
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#
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# Permission is granted to anyone to use this software for any purpose,
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# including commercial applications, and to alter it and redistribute it
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# freely, subject to the following restrictions:
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#
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# 1. The origin of this software must not be misrepresented; you must not
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# claim that you wrote the original software. If you use this software
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# in a product, an acknowledgment in the product documentation would be
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# appreciated but is not required.
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# 2. Altered source versions must be plainly marked as such, and must not be
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# misrepresented as being the original software.
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# 3. This notice may not be removed or altered from any source distribution.
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#
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# Copyright (c) 2008 Greg Hewgill http://hewgill.com
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# Copyright (c) 2011 William Grant <me@williamgrant.id.au>
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__all__ = [
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'EMSA_PKCS1_v1_5_encode',
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'parse_private_key',
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'parse_public_key',
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'RSASSA_PKCS1_v1_5_sign',
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'RSASSA_PKCS1_v1_5_verify',
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]
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from dkim.asn1 import (
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asn1_build,
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asn1_parse,
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BIT_STRING,
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INTEGER,
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SEQUENCE,
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OBJECT_IDENTIFIER,
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OCTET_STRING,
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NULL,
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)
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ASN1_Object = [
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(SEQUENCE, [
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(SEQUENCE, [
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(OBJECT_IDENTIFIER,),
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(NULL,),
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]),
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(BIT_STRING,),
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])
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]
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ASN1_RSAPublicKey = [
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(SEQUENCE, [
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(INTEGER,),
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(INTEGER,),
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])
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]
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ASN1_RSAPrivateKey = [
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(SEQUENCE, [
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(INTEGER,),
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(INTEGER,),
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(INTEGER,),
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(INTEGER,),
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(INTEGER,),
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(INTEGER,),
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(INTEGER,),
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(INTEGER,),
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(INTEGER,),
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])
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]
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def parse_public_key(data):
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x = asn1_parse(ASN1_Object, data)
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# Not sure why the [1:] is necessary to skip a byte.
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pkd = asn1_parse(ASN1_RSAPublicKey, x[0][1][1:])
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pk = {
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'modulus': pkd[0][0],
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'publicExponent': pkd[0][1],
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}
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return pk
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def parse_private_key(data):
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pka = asn1_parse(ASN1_RSAPrivateKey, data)
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pk = {
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'version': pka[0][0],
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'modulus': pka[0][1],
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'publicExponent': pka[0][2],
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'privateExponent': pka[0][3],
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'prime1': pka[0][4],
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'prime2': pka[0][5],
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'exponent1': pka[0][6],
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'exponent2': pka[0][7],
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'coefficient': pka[0][8],
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}
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return pk
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def EMSA_PKCS1_v1_5_encode(digest, modlen, hashid):
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dinfo = asn1_build(
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(SEQUENCE, [
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(SEQUENCE, [
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(OBJECT_IDENTIFIER, hashid),
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(NULL, None),
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]),
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(OCTET_STRING, digest),
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]),
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)
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if len(dinfo)+3 > modlen:
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raise Exception("Hash too large for modulus") # XXX: DKIMException
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return "\x00\x01"+"\xff"*(modlen-len(dinfo)-3)+"\x00"+dinfo
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def str2int(s):
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"""Convert an octet string to an integer.
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Octet string assumed to represent a positive integer.
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"""
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r = 0
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for c in s:
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r = (r << 8) | ord(c)
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return r
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def int2str(n, length = -1):
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"""Convert an integer to an octet string. Number must be positive.
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@param n: Number to convert.
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@param length: Minimum length, or -1 to return the smallest number of
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bytes that represent the integer.
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"""
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assert n >= 0
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r = []
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while length < 0 or len(r) < length:
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r.append(chr(n & 0xff))
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n >>= 8
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if length < 0 and n == 0:
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break
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r.reverse()
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assert length < 0 or len(r) == length
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return ''.join(r)
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def perform_rsa(input, exponent, modulus, modlen):
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return int2str(pow(str2int(input), exponent, modulus), modlen)
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def RSASSA_PKCS1_v1_5_sign(digest, hashid, private_exponent, modulus):
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modlen = len(int2str(modulus))
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encoded_digest = EMSA_PKCS1_v1_5_encode(digest, modlen, hashid)
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return perform_rsa(encoded_digest, private_exponent, modulus, modlen)
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def RSASSA_PKCS1_v1_5_verify(digest, hashid, signature, public_exponent,
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modulus):
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modlen = len(int2str(modulus))
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encoded_digest = EMSA_PKCS1_v1_5_encode(digest, modlen, hashid)
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signed_digest = perform_rsa(signature, public_exponent, modulus, modlen)
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return encoded_digest == signed_digest
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