Module: PWN::SDR::Decoder::GSM

Defined in:
lib/pwn/sdr/decoder/gsm.rb

Overview

Pure-Ruby GSM (2G) BCCH activity detector.

GSM is 270.833 kbit/s GMSK across a 200 kHz channel — physically unrecoverable from a 48 kHz demodulated-audio tap and too fast for interpreted Ruby to demodulate from raw I/Q in real time. Rather than shell out to grgsm_livemon_headless + tshark, this module runs Base.run_detector to characterise BCCH/CCCH burst structure (577 μs slots × 8 = 4.615 ms TDMA frame) natively. parse_line is retained for offline GSMTAP-tshark pipe-delimited analysis.

Constant Summary collapse

TSHARK_FIELDS = 
%w[
  frame.time gsmtap.arfcn gsmtap.chan_type gsm_a.imsi gsm_a.tmsi
  e212.mcc e212.mnc gsm_a.lac gsm_a.bssmap.cell_ci gsm_a.dtap.msg_rr_type
].freeze

Class Method Summary collapse

Class Method Details

.authors ⇒ Object

Author(s)

0day Inc. support@0dayinc.com



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# File 'lib/pwn/sdr/decoder/gsm.rb', line 68

public_class_method def self.authors
  "AUTHOR(S):\n  0day Inc. <support@0dayinc.com>\n"
end

.decode(opts = {}) ⇒ Object

Supported Method Parameters

PWN::SDR::Decoder::GSM.decode( freq_obj: 'required - freq_obj returned from PWN::SDR::GQRX.init_freq' )



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# File 'lib/pwn/sdr/decoder/gsm.rb', line 26

public_class_method def self.decode(opts = {})
  freq_obj = opts[:freq_obj]
  PWN::SDR::Decoder::Base.run_detector(
    freq_obj: freq_obj,
    protocol: 'GSM',
    note: '270.833 kbit/s GMSK exceeds audio-tap Nyquist; native mode reports TDMA burst duty/energy only. Feed captured GSMTAP-tshark fields to .parse_line for MCC/MNC/LAC/CI/IMSI.',
    threshold: 5.0,
    describe: proc { |b|
      frames = (b[:duration_ms] / 4.615).round
      { modulation: 'GMSK', symbol_rate: 270_833, tdma_frames: frames, classification: frames > 10 ? 'BCCH/CCCH-continuous' : 'RACH/paging-burst' }
    }
  )
end

.help ⇒ Object

Display Usage for this Module



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# File 'lib/pwn/sdr/decoder/gsm.rb', line 74

public_class_method def self.help
  puts "USAGE (ruby-native detector, no external binaries):
    #{self}.decode(
      freq_obj: 'required - freq_obj returned from PWN::SDR::GQRX.init_freq'
    )

    #{self}.parse_line(line: 'ts|arfcn|chan|imsi|tmsi|mcc|mnc|lac|ci|rr')

    #{self}.authors
  "
end

.parse_line(opts = {}) ⇒ Object

Supported Method Parameters

PWN::SDR::Decoder::GSM.parse_line(line: 'ts|arfcn|chan|imsi|tmsi|mcc|mnc|lac|ci|rr')



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# File 'lib/pwn/sdr/decoder/gsm.rb', line 43

public_class_method def self.parse_line(opts = {})
  line = opts[:line].to_s
  f = line.split('|', -1)
  out = {
    protocol: 'GSM', frame_time: f[0], arfcn: f[1], chan_type: f[2],
    imsi: f[3], tmsi: f[4], mcc: f[5], mnc: f[6], lac: f[7],
    cell_id: f[8], rr_msg_type: f[9]
  }.reject { |_, v| v.to_s.empty? }
  if out[:imsi].to_s.length.between?(14, 16)
    out[:imsi_mcc]  = out[:imsi][0, 3]
    out[:imsi_mnc]  = out[:imsi][3, 3]
    out[:imsi_msin] = out[:imsi][6..]
  end
  bits = []
  bits << "ARFCN=#{out[:arfcn]}" if out[:arfcn]
  bits << "MCC/MNC=#{out[:mcc]}/#{out[:mnc]}" if out[:mcc]
  bits << "LAC=#{out[:lac]} CI=#{out[:cell_id]}" if out[:lac]
  bits << "IMSI=#{out[:imsi]}" if out[:imsi]
  bits << "TMSI=#{out[:tmsi]}" if out[:tmsi]
  out[:summary] = "GSM #{bits.join(' ')}".strip
  out
end