ThomasV
10 years ago
2 changed files with 185 additions and 220 deletions
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# This program is free software; you can redistribute it and/or modify |
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# it under the terms of the GNU General Public License as published by |
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# the Free Software Foundation; either version 2 of the License, or |
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# (at your option) any later version. |
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# |
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# This program is distributed in the hope that it will be useful, |
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# but WITHOUT ANY WARRANTY; without even the implied warranty of |
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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# GNU General Public License for more details. |
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# |
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# You should have received a copy of the GNU General Public License |
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# along with this program; if not, write to the Free Software |
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, |
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# MA 02110-1301, USA. |
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# This is a simple and fast ASN1 decoder without external libraries. |
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# |
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# In order to browse through the ASN1 structure you need only 3 |
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# functions allowing you to navigate: |
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# asn1_node_root(...), asn1_node_next(...) and asn1_node_first_child(...) |
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# |
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####################### BEGIN ASN1 DECODER ############################ |
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# Author: Jens Getreu, 8.11.2014 |
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##### NAVIGATE |
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# The following 4 functions are all you need to parse an ASN1 structure |
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# gets the first ASN1 structure in der |
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def asn1_node_root(der): |
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return asn1_read_length(der,0) |
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# gets the next ASN1 structure following (ixs,ixf,ixl) |
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def asn1_node_next(der, (ixs,ixf,ixl)): |
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return asn1_read_length(der,ixl+1) |
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# opens the container (ixs,ixf,ixl) and returns the first ASN1 inside |
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def asn1_node_first_child(der, (ixs,ixf,ixl)): |
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if ord(der[ixs]) & 0x20 != 0x20: |
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raise ValueError('Error: can only open constructed types. ' |
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+'Found type: 0x'+der[ixs].encode("hex")) |
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return asn1_read_length(der,ixf) |
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# is true if one ASN1 chunk is inside another chunk. |
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def asn1_node_is_child_of((ixs,ixf,ixl), (jxs,jxf,jxl)): |
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return ( (ixf <= jxs ) and (jxl <= ixl) ) or \ |
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( (jxf <= ixs ) and (ixl <= jxl) ) |
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##### END NAVIGATE |
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##### ACCESS PRIMITIVES |
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# get content and verify type byte |
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def asn1_get_value_of_type(der,(ixs,ixf,ixl),asn1_type): |
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asn1_type_table = { |
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'BOOLEAN': 0x01, 'INTEGER': 0x02, |
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'BIT STRING': 0x03, 'OCTET STRING': 0x04, |
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'NULL': 0x05, 'OBJECT IDENTIFIER': 0x06, |
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'SEQUENCE': 0x70, 'SET': 0x71, |
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'PrintableString': 0x13, 'IA5String': 0x16, |
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'UTCTime': 0x17, 'ENUMERATED': 0x0A, |
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'UTF8String': 0x0C, 'PrintableString': 0x13, |
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} |
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if asn1_type_table[asn1_type] != ord(der[ixs]): |
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raise ValueError('Error: Expected type was: '+ |
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hex(asn1_type_table[asn1_type])+ |
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' Found: 0x'+der[ixs].encode('hex')) |
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return der[ixf:ixl+1] |
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# get value |
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def asn1_get_value(der,(ixs,ixf,ixl)): |
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return der[ixf:ixl+1] |
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# get type+length+value |
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def asn1_get_all(der,(ixs,ixf,ixl)): |
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return der[ixs:ixl+1] |
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##### END ACCESS PRIMITIVES |
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##### HELPER FUNCTIONS |
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# converter |
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def bitstr_to_bytestr(bitstr): |
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if bitstr[0] != '\x00': |
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raise ValueError('Error: only 00 padded bitstr can be converted to bytestr!') |
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return bitstr[1:] |
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# converter |
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def bytestr_to_int(s): |
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# converts bytestring to integer |
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i = 0 |
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for char in s: |
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i <<= 8 |
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i |= ord(char) |
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return i |
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# ix points to the first byte of the asn1 structure |
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# Returns first byte pointer, first content byte pointer and last. |
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def asn1_read_length(der,ix): |
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first= ord(der[ix+1]) |
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if (ord(der[ix+1]) & 0x80) == 0: |
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length = first |
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ix_first_content_byte = ix+2 |
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ix_last_content_byte = ix_first_content_byte + length -1 |
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else: |
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lengthbytes = first & 0x7F |
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length = bytestr_to_int(der[ix+2:ix+2+lengthbytes]) |
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ix_first_content_byte = ix+2+lengthbytes |
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ix_last_content_byte = ix_first_content_byte + length -1 |
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return (ix,ix_first_content_byte,ix_last_content_byte) |
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##### END HELPER FUNCTIONS |
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####################### END ASN1 DECODER ############################ |
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def decode_OID(s): |
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s = map(ord, s) |
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r = [] |
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r.append(s[0] / 40) |
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r.append(s[0] % 40) |
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k = 0 |
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for i in s[1:]: |
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if i < 128: |
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r.append(i + 128*k) |
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k = 0 |
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else: |
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k = (i - 128) + 128*k |
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return '.'.join(map(str, r)) |
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def encode_OID(oid): |
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x = map(int, oid.split('.')) |
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s = chr(x[0]*40 + x[1]) |
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for i in x[2:]: |
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ss = chr(i % 128) |
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while i > 128: |
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i = i / 128 |
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ss = chr(128 + i % 128) + ss |
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s += ss |
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return s |
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def asn1_get_children(der, i): |
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nodes = [] |
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ii = asn1_node_first_child(der,i) |
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nodes.append(ii) |
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while ii[2]<i[2]: |
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ii = asn1_node_next(der,ii) |
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nodes.append(ii) |
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return nodes |
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def asn1_get_sequence(s): |
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return map(lambda j: asn1_get_value(s, j), asn1_get_children(s, asn1_node_root(s))) |
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def asn1_get_dict(der, i): |
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p = {} |
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for ii in asn1_get_children(der, i): |
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for iii in asn1_get_children(der, ii): |
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iiii = asn1_node_first_child(der, iii) |
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oid = decode_OID(asn1_get_value_of_type(der, iiii, 'OBJECT IDENTIFIER')) |
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iiii = asn1_node_next(der, iiii) |
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value = asn1_get_value(der, iiii) |
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p[oid] = value |
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return p |
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