Class: BlockCipherKit::AES256CBCScheme

Inherits:
BaseScheme
  • Object
show all
Defined in:
lib/block_cipher_kit/aes_256_cbc_scheme.rb

Constant Summary collapse

IV_LENGTH = 
16

Instance Method Summary collapse

Methods inherited from BaseScheme

#decrypt_range, #read_copy_stream_via_cipher, #write_copy_stream_via_cipher

Constructor Details

#initialize(encryption_key, iv_generator: SecureRandom) ⇒ AES256CBCScheme

Returns a new instance of AES256CBCScheme.

Raises:

  • (ArgumentError) 


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# File 'lib/block_cipher_kit/aes_256_cbc_scheme.rb', line 6

def initialize(encryption_key, iv_generator: SecureRandom)
  raise ArgumentError, "#{required_encryption_key_length} bytes of key material needed, at the minimum" unless encryption_key.bytesize >= required_encryption_key_length
  @iv_generator = iv_generator
  @key = BlockCipherKit::KeyMaterial.new(encryption_key.byteslice(0, 32))
end

Instance Method Details

#required_encryption_key_length ⇒ Object 



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# File 'lib/block_cipher_kit/aes_256_cbc_scheme.rb', line 12

def required_encryption_key_length
  32
end

#streaming_decrypt(from_ciphertext_io:, into_plaintext_io: nil, &blk) ⇒ Object 



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# File 'lib/block_cipher_kit/aes_256_cbc_scheme.rb', line 16

def streaming_decrypt(from_ciphertext_io:, into_plaintext_io: nil, &blk)
  cipher = OpenSSL::Cipher.new("aes-256-cbc")
  cipher.decrypt
  cipher.iv = from_ciphertext_io.read(IV_LENGTH)
  cipher.key = @key
  read_copy_stream_via_cipher(source_io: from_ciphertext_io, cipher: cipher, destination_io: into_plaintext_io, &blk)
end

#streaming_decrypt_range(from_ciphertext_io:, range:, into_plaintext_io: nil, &blk) ⇒ Object 



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# File 'lib/block_cipher_kit/aes_256_cbc_scheme.rb', line 34

def streaming_decrypt_range(from_ciphertext_io:, range:, into_plaintext_io: nil, &blk)
  block_size = 16
  n_bytes_to_decrypt = range.end - range.begin + 1
  n_blocks_to_skip, offset_into_first_block = range.begin.divmod(block_size)

  cipher = OpenSSL::Cipher.new("aes-256-cbc")
  cipher.decrypt
  cipher.key = @key

  # We need to read the IV either from the start of the IO (the initial IV)
  # or from the block preceding the first block we need to decrypt
  from_ciphertext_io.seek(from_ciphertext_io.pos + (n_blocks_to_skip * block_size))
  cipher.iv = from_ciphertext_io.read(IV_LENGTH)

  writable = BlockCipherKit::BlockWritable.new(into_plaintext_io, &blk)
  lens_range = offset_into_first_block...(offset_into_first_block + n_bytes_to_decrypt)
  lens = BlockCipherKit::IOLens.new(writable, lens_range)

  # TODO: it seems that if we read only the blocks we touch, we need to call cipher.final to get all the output - the cipher buffers,
  # but if we call .final without having read the entire ciphertext the cipher will barf. This needs to be fixed as it is certainly possible with CBC.
  read_copy_stream_via_cipher(source_io: from_ciphertext_io, destination_io: lens, cipher: cipher, finalize_cipher: true, read_limit: from_ciphertext_io.size - from_ciphertext_io.pos)
end

#streaming_encrypt(into_ciphertext_io:, from_plaintext_io: nil, &blk) ⇒ Object 



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# File 'lib/block_cipher_kit/aes_256_cbc_scheme.rb', line 24

def streaming_encrypt(into_ciphertext_io:, from_plaintext_io: nil, &blk)
  random_iv = @iv_generator.bytes(IV_LENGTH)
  cipher = OpenSSL::Cipher.new("aes-256-cbc")
  cipher.encrypt
  cipher.iv = random_iv
  cipher.key = @key
  into_ciphertext_io.write(random_iv)
  write_copy_stream_via_cipher(source_io: from_plaintext_io, cipher: cipher, destination_io: into_ciphertext_io, &blk)
end