Class: Megar::FileDownloader

Inherits:
Object
  • Object
show all
Includes:
Crypto::Support
Defined in:
lib/megar/adapters/file_downloader.rb

Overview

Encapsulates a file download task. This is intended as a one-shot helper.

Javascript reference implementation: function startdownload2(res,ctx)

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Crypto::Support

#a32_to_base64, #a32_to_str, #accumulate_mac, #aes_cbc_decrypt, #aes_cbc_decrypt_a32, #aes_cbc_encrypt, #aes_cbc_encrypt_a32, #aes_encrypt_a32, #base64_mpi_to_a32, #base64_mpi_to_bn, #base64_to_a32, #base64urldecode, #base64urlencode, #calculate_chunk_mac, #crypto_requirements_met?, #decompose_file_key, #decompose_rsa_private_key, #decompose_rsa_private_key_a32, #decrypt_base64_to_a32, #decrypt_base64_to_str, #decrypt_file_attributes, #decrypt_file_key, #decrypt_key, #decrypt_session_id, #encrypt_file_attributes, #encrypt_key, #get_chunks, #get_file_cipher, #hexstr_to_bstr, #mpi_to_a32, #openssl_rsa_cipher, #openssl_rsa_decrypt, #prepare_key, #prepare_key_pw, #rsa_decrypt, #str_to_a32, #stringhash

Constructor Details

#initialize(options = {}) ⇒ FileDownloader

Returns a new instance of FileDownloader.



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# File 'lib/megar/adapters/file_downloader.rb', line 13

def initialize(options={})
  @file = options[:file]
  @session = @file && @file.session
end

Instance Attribute Details

#file ⇒ Object (readonly)

Returns the value of attribute file.



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# File 'lib/megar/adapters/file_downloader.rb', line 11

def file
  @file
end

#session ⇒ Object (readonly)

Returns the value of attribute session.



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# File 'lib/megar/adapters/file_downloader.rb', line 10

def session
  @session
end

Instance Method Details

#chunk_mac_iv ⇒ Object 



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# File 'lib/megar/adapters/file_downloader.rb', line 76

def chunk_mac_iv
  [iv[0], iv[1], iv[0], iv[1]]
end

#content ⇒ Object

Returns the complete decrypted content. If anything goes wrong here, it’s going to bubble up an unhandled error.

Raises:



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# File 'lib/megar/adapters/file_downloader.rb', line 29

def content
  return unless live_session?
  decoded_content = ''
  calculated_mac = [0, 0, 0, 0]

  decryptor = get_file_cipher(decomposed_key,iv)

  get_chunks(download_size).each do |chunk_start, chunk_size|
    chunk = stream.readpartial(chunk_size)
    decoded_chunk = decryptor.update(chunk)
    decoded_content << decoded_chunk
    calculated_mac = accumulate_mac(decoded_chunk,calculated_mac,decomposed_key,chunk_mac_iv)
  end

  raise Megar::MacVerificationError.new unless ([calculated_mac[0] ^ calculated_mac[1], calculated_mac[2] ^ calculated_mac[3]] == mac)

  decoded_content
end

#decomposed_key ⇒ Object

Returns the file key (shortcut)



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# File 'lib/megar/adapters/file_downloader.rb', line 91

def decomposed_key
  file.decomposed_key
end

#download_attributes ⇒ Object

Returns the decrypted download attributes



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# File 'lib/megar/adapters/file_downloader.rb', line 65

def download_attributes
  if attributes = download_url_response['at']
    decrypt_file_attributes(attributes,decomposed_key)
  end
end

#download_size ⇒ Object

Returns a download size for the file content



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# File 'lib/megar/adapters/file_downloader.rb', line 60

def download_size
  download_url_response['s']
end

#download_url ⇒ Object

Returns a download url for the file content



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# File 'lib/megar/adapters/file_downloader.rb', line 55

def download_url
  download_url_response['g']
end

#download_url_response ⇒ Object

Returns and caches a file download response



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# File 'lib/megar/adapters/file_downloader.rb', line 101

def download_url_response
  @download_url_response ||= if live_session?
    session.get_file_download_url_response(file.id)
  else
    {}
  end
end

#initial_counter_value ⇒ Object

Returns the initial value for AES counter



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# File 'lib/megar/adapters/file_downloader.rb', line 96

def initial_counter_value
  ((iv[0] << 32) + iv[1]) << 64
end

#iv ⇒ Object

Returns the initialisation vector



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# File 'lib/megar/adapters/file_downloader.rb', line 72

def iv
  @iv ||= key[4,2] + [0, 0]
end

#key ⇒ Object

Returns the file key (shortcut)



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# File 'lib/megar/adapters/file_downloader.rb', line 86

def key
  file.key
end

#mac ⇒ Object

Returns the expected MAC for the file



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# File 'lib/megar/adapters/file_downloader.rb', line 81

def mac
  key[6,2]
end

#raw_content ⇒ Object

Returns the complete encrypted content (mainly for testing purposes)



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# File 'lib/megar/adapters/file_downloader.rb', line 49

def raw_content
  return unless live_session?
  stream.read
end

#stream ⇒ Object

Returns an io stream to the file content



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# File 'lib/megar/adapters/file_downloader.rb', line 19

def stream
  return unless live_session?
  @stream ||= if url = download_url
    open(url)
  end
end