parse certificates without pyasn1

lib/asn1tinydecoder.py

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