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# -*- coding: binary -*-
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require 'bindata'
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require 'bigdecimal'
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require 'bigdecimal/util'
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module Rex
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module Proto
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module NTP::Header
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  class NTPShort < BinData::Primitive
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    # see: https://datatracker.ietf.org/doc/html/rfc5905#section-6
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    endian :big
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    uint16  :seconds
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    uint16  :fraction
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    def set(value)
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      value = value.to_d
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      seconds = value.floor
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      self.seconds = seconds
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      self.fraction = ((value - seconds) * BigDecimal(2**16)).round
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    end
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    def get
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      BigDecimal(seconds.value) + (BigDecimal(fraction.value) / BigDecimal(2**16))
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    end
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  end
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  class NTPTimestamp < BinData::Primitive
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    UNIX_EPOCH = Time.utc(1900, 1, 1)
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    # see: https://datatracker.ietf.org/doc/html/rfc5905#section-6
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    endian :big
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    uint32 :seconds
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    uint32 :fraction
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    def get
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      return nil if seconds == 0 && fraction == 0
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      time_in_seconds = seconds + BigDecimal(fraction.to_s) / BigDecimal((2**32).to_s)
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      (UNIX_EPOCH + time_in_seconds).utc
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    end
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    def set(time)
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      if time.nil?
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        seconds = fraction = 0
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      else
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        seconds_since_epoch = time.to_r - UNIX_EPOCH.to_r
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        seconds = seconds_since_epoch.to_i
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        fraction = ((seconds_since_epoch - seconds) * (2**32)).to_i
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      end
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      self.seconds = seconds
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      self.fraction = fraction
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    end
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  end
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  class NTPExtension < BinData::Record
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    endian :big
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    uint16      :ext_type
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    uint16      :ext_length
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    uint8_array :ext_value, initial_length: :ext_length
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  end
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  # A unified structure capable of representing NTP versions 1-4
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  class NTPHeader < BinData::Record
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    # see: https://datatracker.ietf.org/doc/html/rfc958 (NTP v0 - unsupported)
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    # see: https://datatracker.ietf.org/doc/html/rfc1059 (NTP v1)
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    # see: https://datatracker.ietf.org/doc/html/rfc1119 (NTP v2)
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    # see: https://datatracker.ietf.org/doc/html/rfc1305 (NTP v3)
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    # see: https://datatracker.ietf.org/doc/html/rfc5905 (NTP v4)
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    endian :big
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    hide :bytes_remaining_0, :bytes_remaining_1
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    bit2                  :leap_indicator
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    bit3                  :version_number, initial_value: 4, assert: -> { version_number.between?(1, 4) }
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    bit3                  :mode, onlyif: -> { version_number > 1 }
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    resume_byte_alignment
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    uint8                 :stratum
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    int8                  :poll
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    int8                  :precision
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    ntp_short             :root_delay
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    ntp_short             :root_dispersion
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    string                :reference_id, length: 4, trim_padding: true
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    ntp_timestamp         :reference_timestamp
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    ntp_timestamp         :origin_timestamp
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    ntp_timestamp         :receive_timestamp
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    ntp_timestamp         :transmit_timestamp
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    count_bytes_remaining :bytes_remaining_0
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    buffer :extensions, length: -> { bytes_remaining_0 - 20 }, onlyif: :has_extensions? do
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      array :extensions, type: :ntp_extension, read_until: :eof
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    end
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    count_bytes_remaining :bytes_remaining_1
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    uint32                :key_identifier, onlyif: :has_key_identifier?
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    uint8_array           :message_digest, initial_length: OpenSSL::Digest::MD5.new.digest_length, onlyif: :has_message_digest?
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    private
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    def has_extensions?
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      # -20 for the length of the key identifier and message digest which are required when extensions are present
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      bytes_remaining_0 - 20 > 0 && version_number > 3
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    end
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    def has_key_identifier?
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      bytes_remaining_1 > 0 || !key_identifier.clear?
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    end
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    def has_message_digest?
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      bytes_remaining_1 > 4 || !message_digest.clear?
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    end
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  end
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end
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end
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end
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