Method: ECIES::Crypt#kdf

Defined in:
lib/ecies/crypt.rb

#kdf(shared_secret, length, shared_info_suffix) ⇒ String

Key-derivation function, compatible with ANSI-X9.63-KDF

Parameters:

  • shared_secret (String) —

    The shared secret from which the key will be derived.

  • length (Integer) —

    The length of the key to generate.

  • shared_info_suffix (String) —

    The suffix to append to the shared_info.

Returns:

  • (String) —

    Octet string of the derived key.



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# File 'lib/ecies/crypt.rb', line 125

def kdf(shared_secret, length, shared_info_suffix)
  length >=0 or raise "length cannot be negative"
  return "" if length == 0

  if length / @kdf_digest.digest_length >= 0xFF_FF_FF_FF
    raise "length too large"
  end

  io = StringIO.new(String.new)
  counter = 0

  loop do
    counter += 1
    counter_bytes = [counter].pack('N')

    io << @kdf_digest.digest(shared_secret + counter_bytes + @kdf_shared_info + shared_info_suffix)
    if io.pos >= length
      return io.string.byteslice(0, length)
    end
  end
end