--- -- ASN.1 functions. -- -- Large chunks of this code have been ripped right out from snmp.lua. -- -- @copyright Same as Nmap--See https://nmap.org/book/man-legal.html -- -- @author Patrik Karlsson -- @class module -- @name asn1 -- -- Version 0.3 -- Created 01/12/2010 - v0.1 - Created by Patrik Karlsson -- Revised 01/28/2010 - v0.2 - Adapted to create a framework for SNMP, LDAP and future protocols -- Revised 02/02/2010 - v0.3 - Changes: o Re-designed so that ASN1Encoder and ASN1Decoder are separate classes -- o Each script or library should now create its own Encoder and Decoder instance -- local bin = require "bin" local bit = require "bit" local math = require "math" local stdnse = require "stdnse" local string = require "string" local table = require "table" _ENV = stdnse.module("asn1", stdnse.seeall) BERCLASS = { Universal = 0, Application = 64, ContextSpecific = 128, Private = 192 } --- The decoder class -- ASN1Decoder = { new = function(self,o) o = o or {} setmetatable(o, self) self.__index = self return o end, --- Tells the decoder to stop if it detects an error while decoding. -- -- This should probably be the default, but some scripts depend on being -- able to decode stuff while lacking proper ASN1 decoding functions. -- @name ASN1Decoder.setStopOnError -- @param val boolean, true if decoding should stop on error, -- otherwise false (default) setStopOnError = function(self, val) self.stoponerror = val end, --- Registers the base simple type decoders -- @name ASN1Decoder.registerBaseDecoders registerBaseDecoders = function(self) self.decoder = {} -- Boolean self.decoder["01"] = function( self, encStr, elen, pos ) local pos, val = bin.unpack("H", encStr, pos) if val ~= "FF" then return pos, true else return pos, false end end -- Integer self.decoder["02"] = function( self, encStr, elen, pos ) return self.decodeInt(encStr, elen, pos) end -- Octet String self.decoder["04"] = function( self, encStr, elen, pos ) return bin.unpack("A" .. elen, encStr, pos) end -- Null self.decoder["05"] = function( self, encStr, elen, pos ) return pos, false end -- Object Identifier self.decoder["06"] = function( self, encStr, elen, pos ) return self:decodeOID( encStr, elen, pos ) end -- Context specific tags -- self.decoder["30"] = function( self, encStr, elen, pos ) return self:decodeSeq(encStr, elen, pos) end end, --- Table for registering additional tag decoders. -- -- Each index is a tag number as a hex string. Values are ASN1 decoder -- functions. -- @name tagDecoders -- @class table -- @see asn1.decoder --- Template for an ASN1 decoder function. -- @name asn1.decoder -- @class function -- @param self The ASN1Decoder object -- @param encStr Encoded string -- @param elen Length of the object in bytes -- @param pos Current position in the string -- @return The position after decoding -- @return The decoded object --- Allows for registration of additional tag decoders -- @name ASN1Decoder.registerTagDecoders -- @param tagDecoders table containing decoding functions -- @see tagDecoders registerTagDecoders = function(self, tagDecoders) self:registerBaseDecoders() for k, v in pairs(tagDecoders) do self.decoder[k] = v end end, --- Decodes the ASN.1's built-in simple types -- @name ASN1Decoder.decode -- @param encStr Encoded string. -- @param pos Current position in the string. -- @return The position after decoding -- @return The decoded value(s). decode = function(self, encStr, pos) local etype, elen local newpos = pos newpos, etype = bin.unpack("H1", encStr, newpos) newpos, elen = self.decodeLength(encStr, newpos) if self.decoder[etype] then return self.decoder[etype]( self, encStr, elen, newpos ) else stdnse.debug1("no decoder for etype: " .. etype) return newpos, nil end end, --- -- Decodes length part of encoded value according to ASN.1 basic encoding -- rules. -- @name ASN1Decoder.decodeLength -- @param encStr Encoded string. -- @param pos Current position in the string. -- @return The position after decoding. -- @return The length of the following value. decodeLength = function(encStr, pos) local elen pos, elen = bin.unpack('C', encStr, pos) if (elen > 128) then elen = elen - 128 local elenCalc = 0 local elenNext for i = 1, elen do elenCalc = elenCalc * 256 pos, elenNext = bin.unpack("C", encStr, pos) elenCalc = elenCalc + elenNext end elen = elenCalc end return pos, elen end, --- -- Decodes a sequence according to ASN.1 basic encoding rules. -- @name ASN1Decoder.decodeSeq -- @param encStr Encoded string. -- @param len Length of sequence in bytes. -- @param pos Current position in the string. -- @return The position after decoding. -- @return The decoded sequence as a table. decodeSeq = function(self, encStr, len, pos) local seq = {} local sPos = 1 local sStr pos, sStr = bin.unpack("A" .. len, encStr, pos) while (sPos < len) do local newSeq sPos, newSeq = self:decode(sStr, sPos) if ( not(newSeq) and self.stoponerror ) then break end table.insert(seq, newSeq) end return pos, seq end, -- Decode one component of an OID from a byte string. 7 bits of the component -- are stored in each octet, most significant first, with the eighth bit set in -- all octets but the last. These encoding rules come from -- http://luca.ntop.org/Teaching/Appunti/asn1.html, section 5.9 OBJECT -- IDENTIFIER. decode_oid_component = function(encStr, pos) local octet local n = 0 repeat pos, octet = bin.unpack("C", encStr, pos) n = n * 128 + bit.band(0x7F, octet) until octet < 128 return pos, n end, --- Decodes an OID from a sequence of bytes. -- @name ASN1Decoder.decodeOID -- @param encStr Encoded string. -- @param len Length of sequence in bytes. -- @param pos Current position in the string. -- @return The position after decoding. -- @return The OID as an array. decodeOID = function(self, encStr, len, pos) local last local oid = {} local octet last = pos + len - 1 if pos <= last then oid._snmp = '06' pos, octet = bin.unpack("C", encStr, pos) oid[2] = math.fmod(octet, 40) octet = octet - oid[2] oid[1] = octet/40 end while pos <= last do local c pos, c = self.decode_oid_component(encStr, pos) oid[#oid + 1] = c end return pos, oid end, --- -- Decodes an Integer according to ASN.1 basic encoding rules. -- @name ASN1Decoder.decodeInt -- @param encStr Encoded string. -- @param len Length of integer in bytes. -- @param pos Current position in the string. -- @return The position after decoding. -- @return The decoded integer. decodeInt = function(encStr, len, pos) local hexStr pos, hexStr = bin.unpack("H" .. len, encStr, pos) local value = tonumber(hexStr, 16) if (value >= (256^len)/2) then value = value - 256^len end return pos, value end, } --- The encoder class -- ASN1Encoder = { new = function(self) local o = {} setmetatable(o, self) self.__index = self o:registerBaseEncoders() return o end, --- -- Encodes an ASN1 sequence -- @name ASN1Encoder.encodeSeq -- @param seqData A string of sequence data -- @return ASN.1 BER-encoded sequence encodeSeq = function(self, seqData) -- 0x30 = 00110000 = 00 1 10000 -- hex binary Universal Constructed value Data Type = SEQUENCE (16) return bin.pack('HAA' , '30', self.encodeLength(#seqData), seqData) end, --- -- Encodes a given value according to ASN.1 basic encoding rules for SNMP -- packet creation. -- @name ASN1Encoder.encode -- @param val Value to be encoded. -- @return Encoded value. encode = function(self, val) local vtype = type(val) if self.encoder[vtype] then return self.encoder[vtype](self,val) else return nil end return '' end, --- Table for registering additional tag encoders. -- -- Each index is a lua type as a string. Values are ASN1 encoder -- functions. -- @name tagEncoders -- @class table -- @see asn1.encoder --- Template for an ASN1 encoder function. -- @name asn1.encoder -- @param self The ASN1Encoder object -- @param val The value to encode -- @return The encoded object -- @class function --- Allows for registration of additional tag encoders -- @name ASN1Decoder.registerTagEncoders -- @param tagEncoders table containing encoding functions -- @see tagEncoders registerTagEncoders = function(self, tagEncoders) self:registerBaseEncoders() for k, v in pairs(tagEncoders) do self.encoder[k] = v end end, --- Registers the base ASN.1 Simple types encoders -- -- * boolean -- * integer (Lua number) -- * string -- * null (Lua nil) -- @name ASN1Encoder.registerBaseEncoders registerBaseEncoders = function(self) self.encoder = {} -- Boolean encoder self.encoder['boolean'] = function( self, val ) if val then return bin.pack('H','01 01 FF') else return bin.pack('H', '01 01 00') end end -- Table encoder self.encoder['table'] = function( self, val ) assert('table' == type(val), "val is not a table") assert(#val.type > 0, "Table is missing the type field") assert(val.value ~= nil, "Table is missing the value field") return bin.pack("HAA", val.type, self.encodeLength(#val.value), val.value) end -- Integer encoder self.encoder['number'] = function( self, val ) local ival = self.encodeInt(val) local len = self.encodeLength(#ival) return bin.pack('HAA', '02', len, ival) end -- Octet String encoder self.encoder['string'] = function( self, val ) local len = self.encodeLength(#val) return bin.pack('HAA', '04', len, val) end -- Null encoder self.encoder['nil'] = function( self, val ) return bin.pack('H', '05 00') end end, -- Encode one component of an OID as a byte string. 7 bits of the component are -- stored in each octet, most significant first, with the eighth bit set in all -- octets but the last. These encoding rules come from -- http://luca.ntop.org/Teaching/Appunti/asn1.html, section 5.9 OBJECT -- IDENTIFIER. encode_oid_component = function(n) local parts = {} parts[1] = string.char(bit.mod(n, 128)) while n >= 128 do n = bit.rshift(n, 7) parts[#parts + 1] = string.char(bit.mod(n, 128) + 0x80) end return string.reverse(table.concat(parts)) end, --- -- Encodes an Integer according to ASN.1 basic encoding rules. -- @name ASN1Encoder.encodeInt -- @param val Value to be encoded. -- @return Encoded integer. encodeInt = function(val) local lsb = 0 if val > 0 then local valStr = "" while (val > 0) do lsb = math.fmod(val, 256) valStr = valStr .. bin.pack("C", lsb) val = math.floor(val/256) end if lsb > 127 then -- two's complement collision valStr = valStr .. "\0" end return string.reverse(valStr) elseif val < 0 then local i = 1 local tcval = val + 256 -- two's complement while tcval <= 127 do tcval = tcval + 256^i * 255 i = i+1 end local valStr = "" while (tcval > 0) do lsb = math.fmod(tcval, 256) valStr = valStr .. bin.pack("C", lsb) tcval = math.floor(tcval/256) end return string.reverse(valStr) else -- val == 0 return bin.pack("x") end end, --- -- Encodes the length part of a ASN.1 encoding triplet using the "primitive, -- definite-length" method. -- @name ASN1Encoder.encodeLength -- @param len Length to be encoded. -- @return Encoded length value. encodeLength = function(len) if len < 128 then return string.char(len) else local parts = {} while len > 0 do parts[#parts + 1] = string.char(bit.mod(len, 256)) len = bit.rshift(len, 8) end assert(#parts < 128) return string.char(#parts + 0x80) .. string.reverse(table.concat(parts)) end end } --- Converts a BER encoded type to a numeric value -- -- This allows it to be used in the encoding function -- -- @param class number - see BERCLASS -- @param constructed boolean (true if constructed, false if primitive) -- @param number numeric -- @return number to be used with encode function BERtoInt(class, constructed, number) local asn1_type = class + number if constructed == true then asn1_type = asn1_type + 32 end return asn1_type end --- -- Converts an integer to a BER encoded type table -- -- @param i number containing the value to decode -- @return table with the following entries: -- * class -- * constructed -- * primitive -- * number function intToBER( i ) local ber = {} if bit.band( i, BERCLASS.Application ) == BERCLASS.Application then ber.class = BERCLASS.Application elseif bit.band( i, BERCLASS.ContextSpecific ) == BERCLASS.ContextSpecific then ber.class = BERCLASS.ContextSpecific elseif bit.band( i, BERCLASS.Private ) == BERCLASS.Private then ber.class = BERCLASS.Private else ber.class = BERCLASS.Universal end if bit.band( i, 32 ) == 32 then ber.constructed = true ber.number = i - ber.class - 32 else ber.primitive = true ber.number = i - ber.class end return ber end return _ENV;