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Filename :
der.py
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from __future__ import division import binascii import base64 from .six import int2byte, b, integer_types, text_type class UnexpectedDER(Exception): pass def encode_constructed(tag, value): return int2byte(0xa0+tag) + encode_length(len(value)) + value def encode_integer(r): assert r >= 0 # can't support negative numbers yet h = ("%x" % r).encode() if len(h) % 2: h = b("0") + h s = binascii.unhexlify(h) num = s[0] if isinstance(s[0], integer_types) else ord(s[0]) if num <= 0x7f: return b("\x02") + int2byte(len(s)) + s else: # DER integers are two's complement, so if the first byte is # 0x80-0xff then we need an extra 0x00 byte to prevent it from # looking negative. return b("\x02") + int2byte(len(s)+1) + b("\x00") + s def encode_bitstring(s): return b("\x03") + encode_length(len(s)) + s def encode_octet_string(s): return b("\x04") + encode_length(len(s)) + s def encode_oid(first, second, *pieces): assert first <= 2 assert second <= 39 encoded_pieces = [int2byte(40*first+second)] + [encode_number(p) for p in pieces] body = b('').join(encoded_pieces) return b('\x06') + encode_length(len(body)) + body def encode_sequence(*encoded_pieces): total_len = sum([len(p) for p in encoded_pieces]) return b('\x30') + encode_length(total_len) + b('').join(encoded_pieces) def encode_number(n): b128_digits = [] while n: b128_digits.insert(0, (n & 0x7f) | 0x80) n = n >> 7 if not b128_digits: b128_digits.append(0) b128_digits[-1] &= 0x7f return b('').join([int2byte(d) for d in b128_digits]) def remove_constructed(string): s0 = string[0] if isinstance(string[0], integer_types) else ord(string[0]) if (s0 & 0xe0) != 0xa0: raise UnexpectedDER("wanted constructed tag (0xa0-0xbf), got 0x%02x" % s0) tag = s0 & 0x1f length, llen = read_length(string[1:]) body = string[1+llen:1+llen+length] rest = string[1+llen+length:] return tag, body, rest def remove_sequence(string): if not string.startswith(b("\x30")): n = string[0] if isinstance(string[0], integer_types) else ord(string[0]) raise UnexpectedDER("wanted sequence (0x30), got 0x%02x" % n) length, lengthlength = read_length(string[1:]) endseq = 1+lengthlength+length return string[1+lengthlength:endseq], string[endseq:] def remove_octet_string(string): if not string.startswith(b("\x04")): n = string[0] if isinstance(string[0], integer_types) else ord(string[0]) raise UnexpectedDER("wanted octetstring (0x04), got 0x%02x" % n) length, llen = read_length(string[1:]) body = string[1+llen:1+llen+length] rest = string[1+llen+length:] return body, rest def remove_object(string): if not string.startswith(b("\x06")): n = string[0] if isinstance(string[0], integer_types) else ord(string[0]) raise UnexpectedDER("wanted object (0x06), got 0x%02x" % n) length, lengthlength = read_length(string[1:]) body = string[1+lengthlength:1+lengthlength+length] rest = string[1+lengthlength+length:] numbers = [] while body: n, ll = read_number(body) numbers.append(n) body = body[ll:] n0 = numbers.pop(0) first = n0//40 second = n0-(40*first) numbers.insert(0, first) numbers.insert(1, second) return tuple(numbers), rest def remove_integer(string): if not string.startswith(b("\x02")): n = string[0] if isinstance(string[0], integer_types) else ord(string[0]) raise UnexpectedDER("wanted integer (0x02), got 0x%02x" % n) length, llen = read_length(string[1:]) numberbytes = string[1+llen:1+llen+length] rest = string[1+llen+length:] nbytes = numberbytes[0] if isinstance(numberbytes[0], integer_types) else ord(numberbytes[0]) assert nbytes < 0x80 # can't support negative numbers yet return int(binascii.hexlify(numberbytes), 16), rest def read_number(string): number = 0 llen = 0 # base-128 big endian, with b7 set in all but the last byte while True: if llen > len(string): raise UnexpectedDER("ran out of length bytes") number = number << 7 d = string[llen] if isinstance(string[llen], integer_types) else ord(string[llen]) number += (d & 0x7f) llen += 1 if not d & 0x80: break return number, llen def encode_length(l): assert l >= 0 if l < 0x80: return int2byte(l) s = ("%x" % l).encode() if len(s)%2: s = b("0")+s s = binascii.unhexlify(s) llen = len(s) return int2byte(0x80|llen) + s def read_length(string): num = string[0] if isinstance(string[0], integer_types) else ord(string[0]) if not (num & 0x80): # short form return (num & 0x7f), 1 # else long-form: b0&0x7f is number of additional base256 length bytes, # big-endian llen = num & 0x7f if llen > len(string)-1: raise UnexpectedDER("ran out of length bytes") return int(binascii.hexlify(string[1:1+llen]), 16), 1+llen def remove_bitstring(string): num = string[0] if isinstance(string[0], integer_types) else ord(string[0]) if not string.startswith(b("\x03")): raise UnexpectedDER("wanted bitstring (0x03), got 0x%02x" % num) length, llen = read_length(string[1:]) body = string[1+llen:1+llen+length] rest = string[1+llen+length:] return body, rest # SEQUENCE([1, STRING(secexp), cont[0], OBJECT(curvename), cont[1], BINTSTRING) # signatures: (from RFC3279) # ansi-X9-62 OBJECT IDENTIFIER ::= { # iso(1) member-body(2) us(840) 10045 } # # id-ecSigType OBJECT IDENTIFIER ::= { # ansi-X9-62 signatures(4) } # ecdsa-with-SHA1 OBJECT IDENTIFIER ::= { # id-ecSigType 1 } ## so 1,2,840,10045,4,1 ## so 0x42, .. .. # Ecdsa-Sig-Value ::= SEQUENCE { # r INTEGER, # s INTEGER } # id-public-key-type OBJECT IDENTIFIER ::= { ansi-X9.62 2 } # # id-ecPublicKey OBJECT IDENTIFIER ::= { id-publicKeyType 1 } # I think the secp224r1 identifier is (t=06,l=05,v=2b81040021) # secp224r1 OBJECT IDENTIFIER ::= { # iso(1) identified-organization(3) certicom(132) curve(0) 33 } # and the secp384r1 is (t=06,l=05,v=2b81040022) # secp384r1 OBJECT IDENTIFIER ::= { # iso(1) identified-organization(3) certicom(132) curve(0) 34 } def unpem(pem): if isinstance(pem, text_type): pem = pem.encode() d = b("").join([l.strip() for l in pem.split(b("\n")) if l and not l.startswith(b("-----"))]) return base64.b64decode(d) def topem(der, name): b64 = base64.b64encode(der) lines = [("-----BEGIN %s-----\n" % name).encode()] lines.extend([b64[start:start+64]+b("\n") for start in range(0, len(b64), 64)]) lines.append(("-----END %s-----\n" % name).encode()) return b("").join(lines)