Module: RobocapCenc::SDK::Mp4Cenc

Defined in:
lib/robocap/sdk/mp4_cenc.rb

Constant Summary collapse

CEKA_TAG = 
'cenc_cek_wrapped_b64'
CUSTOMER_ID_TAG = 
'cenc_customer_id'
CUSTOMER_ID_FALLBACK_TAG = 
'deviceid'
HOST_TAG = 
'host'
KID_TAG = 
'cenc_kid_hex'
CENC_WRAPPED_ALGO_TAG = 
'cenc_wrapped_algo'
CENC_STRIP_TAGS_ON_DECRYPT = 
[
  CEKA_TAG,
  CENC_WRAPPED_ALGO_TAG,
].freeze

Class Method Summary collapse

Class Method Details

.detect_product_line(mp4_path) ⇒ Object

Product line is derived from the filename prefix, which decides whether the vault is keyed by the deviceid or the host tag.



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# File 'lib/robocap/sdk/mp4_cenc.rb', line 86

def detect_product_line(mp4_path)
  stem = Pathname(mp4_path).basename('.*').to_s.downcase
  return PRODUCT_LINE_ROBOWRIST if stem.start_with?('robowrist_')
  return PRODUCT_LINE_ROBOCAP if stem.start_with?('robocap_')
  PRODUCT_LINE_LEGACY
end

.has_cenc_tags(mp4_path, ffprobe_executable: nil) ⇒ Object 



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# File 'lib/robocap/sdk/mp4_cenc.rb', line 144

def has_cenc_tags(mp4_path, ffprobe_executable: nil)
  path = Pathname(mp4_path).expand_path
  tags = read_format_tags(path, ffprobe_executable: ffprobe_executable)
  has_required_tags_for_product?(tags, detect_product_line(path))
rescue Error
  false
end

.load_cenc_metadata(mp4_path, ffprobe_executable: nil) ⇒ Object 



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# File 'lib/robocap/sdk/mp4_cenc.rb', line 136

def load_cenc_metadata(mp4_path, ffprobe_executable: nil)
  path = Pathname(mp4_path).expand_path
  tags = read_format_tags(path, ffprobe_executable: ffprobe_executable)
  parse_cenc_metadata_from_tags(
    tags, mp4_path: path, product_line: detect_product_line(path),
  )
end

.parse_cenc_metadata_from_tags(tags, mp4_path: nil, product_line: nil) ⇒ Object 



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# File 'lib/robocap/sdk/mp4_cenc.rb', line 93

def parse_cenc_metadata_from_tags(tags, mp4_path: nil, product_line: nil)
  unless tags[CEKA_TAG] && !tags[CEKA_TAG].empty?
    raise Error.new(
      code: ErrorCode::ERR_CENC_TAGS_MISSING,
      message: "Missing CENC tags: #{CEKA_TAG}",
    )
  end

  line = product_line
  line ||= mp4_path ? detect_product_line(mp4_path) : PRODUCT_LINE_LEGACY

  customer_id = resolve_vault_customer_id(tags, line)

  begin
    cek_wrapped = Base64.strict_decode64(tags[CEKA_TAG])
  rescue ArgumentError
    raise Error.new(
      code: ErrorCode::ERR_CENC_TAGS_MISSING,
      message: 'Invalid cenc_cek_wrapped_b64 Base64',
    )
  end

  unless cek_wrapped.bytesize == Config::RSA_2048_CIPHERTEXT_BYTES
    raise Error.new(
      code: ErrorCode::ERR_CENC_CEKA_WRAP,
      message: "Wrapped CEK must be #{Config::RSA_2048_CIPHERTEXT_BYTES} bytes",
    )
  end

  kid = tags[KID_TAG]
  kid = kid.strip.downcase if kid
  kid = nil if kid && kid.empty?

  CencMp4Metadata.new(
    customer_id: customer_id,
    cek_wrapped: cek_wrapped,
    kid_hex: kid,
    product_line: line,
    tag_deviceid: tag_value(tags, CUSTOMER_ID_FALLBACK_TAG) || tag_value(tags, CUSTOMER_ID_TAG),
    tag_host: tag_value(tags, HOST_TAG),
  )
end

.read_format_tags(mp4_path, ffprobe_executable: nil) ⇒ Object 



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# File 'lib/robocap/sdk/mp4_cenc.rb', line 47

def read_format_tags(mp4_path, ffprobe_executable: nil)
  path = Pathname(mp4_path).expand_path
  unless path.file?
    raise Error.new(
      code: ErrorCode::ERR_CENC_TAGS_MISSING,
      message: "MP4 file not found: #{path}",
    )
  end
  exe = FfmpegCli.resolve_ffprobe_executable(ffprobe_executable)
  stdout, stderr, status = FfmpegCli.open3_capture3(
    exe, '-v', 'error', '-show_format', '-print_format', 'json', path.to_s,
  )
  unless status.exitstatus.zero?
    raise Error.new(
      code: ErrorCode::ERR_CENC_FFPROBE_FAILED,
      message: "ffprobe failed: #{stderr}",
    )
  end

  payload = parse_ffprobe_json(stdout)
  fmt = payload['format']
  unless fmt.is_a?(Hash)
    raise Error.new(
      code: ErrorCode::ERR_CENC_TAGS_MISSING,
      message: 'ffprobe output missing format section',
    )
  end
  tags = fmt['tags']
  unless tags.is_a?(Hash)
    raise Error.new(
      code: ErrorCode::ERR_CENC_TAGS_MISSING,
      message: 'MP4 has no format metadata tags',
    )
  end
  tags.transform_keys(&:to_s).transform_values(&:to_s)
end

.verify_session_device_id(session_device_id, tags, product_line) ⇒ Object

Binds a caller-supplied device id to the tags embedded in the MP4 so a capture cannot be decrypted under a different device's session.



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# File 'lib/robocap/sdk/mp4_cenc.rb', line 154

def verify_session_device_id(session_device_id, tags, product_line)
  normalized = normalize_session_device_id(session_device_id)

  if product_line == PRODUCT_LINE_ROBOWRIST
    expected = tag_value(tags, HOST_TAG)
    field = HOST_TAG
  else
    expected = tag_value(tags, CUSTOMER_ID_TAG) || tag_value(tags, CUSTOMER_ID_FALLBACK_TAG)
    field = CUSTOMER_ID_TAG
  end

  assert_session_device_id_matches(expected, normalized, field)
end

.verify_session_device_id_from_metadata(session_device_id, meta) ⇒ Object 



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# File 'lib/robocap/sdk/mp4_cenc.rb', line 168

def verify_session_device_id_from_metadata(session_device_id, meta)
  normalized = normalize_session_device_id(session_device_id)

  if meta.product_line == PRODUCT_LINE_ROBOWRIST
    expected = meta.tag_host
    field = HOST_TAG
  else
    expected = meta.tag_deviceid
    field = CUSTOMER_ID_FALLBACK_TAG
  end

  assert_session_device_id_matches(expected, normalized, field)
end