124 lines
3.7 KiB
Python
124 lines
3.7 KiB
Python
# 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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