Class: EllipticCurve::Utils::Der

Inherits:
Object
  • Object
show all
Defined in:
lib/utils/der.rb

Defined Under Namespace

Modules: DerFieldType

Class Method Summary collapse

Class Method Details

._encodeInteger(number) ⇒ Object 



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# File 'lib/utils/der.rb', line 115

def self._encodeInteger(number)
    hexadecimal = Utils::Binary.hexFromInt(number.abs)
    if number < 0
        bitCount = hexadecimal.length * 4
        twosComplement = (2 ** bitCount) + number
        return Utils::Binary.hexFromInt(twosComplement)
    end
    bits = Utils::Binary.bitsFromHex(hexadecimal[0])
    if bits[0] == "1"
        hexadecimal = "00" + hexadecimal
    end
    return hexadecimal
end

._generateLengthBytes(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 147

def self._generateLengthBytes(hexadecimal)
    size = hexadecimal.length.div(2)
    length = Utils::Binary.hexFromInt(size)
    if size < 128
        return length.rjust(2, "0")
    end
    lengthLength = 128 + length.length.div(2)
    return Utils::Binary.hexFromInt(lengthLength) + length
end

._getTagData(tag) ⇒ Object 



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# File 'lib/utils/der.rb', line 157

def self._getTagData(tag)
    bits = Utils::Binary.bitsFromHex(tag)
    bit8 = bits[0]
    bit7 = bits[1]
    bit6 = bits[2]

    tagClass = {
        "0" => {
            "0" => "universal",
            "1" => "application",
        },
        "1" => {
            "0" => "context-specific",
            "1" => "private",
        },
    }[bit8][bit7]
    
    isConstructed = bit6 == "1"

    return {
        "class": tagClass,
        "isConstructed": isConstructed,
        "type": @_hexTagToType[tag],
    }
end

._parseAny(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 84

def self._parseAny(hexadecimal)
    return hexadecimal
end

._parseInteger(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 105

def self._parseInteger(hexadecimal)
    integer = Utils::Binary.intFromHex(hexadecimal)
    bits = Utils::Binary.bitsFromHex(hexadecimal[0])
    if bits[0] == "0" # negative numbers are encoded using two's complement
        return integer
    end
    bitCount = 4 * hexadecimal.length
    return integer - (2 ** bitCount)
end

._parseNull(_content) ⇒ Object 



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# File 'lib/utils/der.rb', line 101

def self._parseNull(_content)
    return nil
end

._parseOid(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 88

def self._parseOid(hexadecimal)
    return Utils::Oid.oidFromHex(hexadecimal)
end

._parseString(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 97

def self._parseString(hexadecimal)
    return Utils::Binary.byteStringFromHex(hexadecimal)
end

._parseTime(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 92

def self._parseTime(hexadecimal)
    string = self._parseString(hexadecimal)
    return DateTime.strptime(string, "%y%m%d%H%M%SZ")
end

._readLengthBytes(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 129

def self._readLengthBytes(hexadecimal)
    lengthBytes = 2
    lengthIndicator = Utils::Binary.intFromHex(hexadecimal[0, lengthBytes])
    isShortForm = lengthIndicator < 128  # checks if first bit of byte is 1 (a.k.a. short-form)
    if isShortForm
        length = lengthIndicator * 2
        return length, lengthBytes
    end

    lengthLength = lengthIndicator - 128  # nullifies first bit of byte (only used as long-form flag)
    if lengthLength == 0
        raise Exception.new("indefinite length encoding located in DER")
    end
    lengthBytes += 2 * lengthLength
    length = Utils::Binary.intFromHex(hexadecimal[2, lengthBytes]) * 2
    return length, lengthBytes
end

.encodeConstructed(*encodedValues) ⇒ Object 



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# File 'lib/utils/der.rb', line 38

def self.encodeConstructed(*encodedValues)
    return self.encodePrimitive(DerFieldType.sequence, encodedValues.join(""))
end

.encodePrimitive(tagType, value) ⇒ Object 



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# File 'lib/utils/der.rb', line 42

def self.encodePrimitive(tagType, value)
    if tagType == DerFieldType.integer
        value = self._encodeInteger(value)
    end
    if tagType == DerFieldType.object
        value = Utils::Oid.oidToHex(value)
    end
    return "#{@_typeToHexTag[tagType]}#{self._generateLengthBytes(value)}#{value}"
end

.parse(hexadecimal) ⇒ Object 



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# File 'lib/utils/der.rb', line 52

def self.parse(hexadecimal)
    if hexadecimal.class == String && hexadecimal.empty?
        return []
    elsif not hexadecimal then 
        return [] 
    end
    
    typeByte, hexadecimal = hexadecimal[0..1], hexadecimal[2..-1]
    length, lengthBytes = self._readLengthBytes(hexadecimal)
    content = hexadecimal[lengthBytes..lengthBytes + length - 1] 
    hexadecimal = hexadecimal[lengthBytes + length..-1]

    if content.length < length
        raise Exception.new("missing bytes in DER parsing")
    end

    tagData = self._getTagData(typeByte)
    if tagData[:isConstructed]
        content = self.parse(content)
    end

    valueParser = {
        DerFieldType.null => lambda { |content| self._parseNull(content) },
        DerFieldType.object => lambda { |content| self._parseOid(content) },
        DerFieldType.utcTime => lambda { |content| self._parseTime(content) },
        DerFieldType.integer => lambda { |content| self._parseInteger(content) },
        DerFieldType.printableString => lambda { |content| self._parseString(content) },
    }.fetch(tagData[:type], lambda { |content| self._parseAny(content) })

    return [valueParser.call(content)] + self.parse(hexadecimal)
end