Method: Ccrypto::Java::HKDFEngine#derive

Defined in:
lib/ccrypto/java/engines/hkdf_engine.rb

#derive(input, output = :binary) ⇒ Object 



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# File 'lib/ccrypto/java/engines/hkdf_engine.rb', line 62

def derive(input, output = :binary)
  begin

    logger.debug "HKDF config : #{@config.inspect}"

    case @config.digest
    when Symbol, String
      hkdfConf = self.class.find_hkdf_config_by_digest(@config.digest)
      raise HKDFEngineError, "Unsupported digest '#{@config.digest}'" if is_empty?(hkdfConf)
      digest = hkdfConf.first.digest
    when Ccrypto::DigestConfig
      digest = @config.digest
    else
      raise HKDFEngineError, "Unsupported digest '#{@config.digest}'"
    end

    logger.debug "Digest for HKDF : #{digest.inspect}"

    begin
      dig = Ccrypto::Java::DigestEngine.instance(digest) 
    rescue Exception => ex
      raise KDFEngineException, "Failed to initialize digest engine. Error was : #{ex}"
    end

    #bcDigest = Ccrypto::Java::DigestEngine.to_bc_digest_inst(digest.provider_config[:algo_name])
    #raise KDFEngineException, "Digest '#{digest.algo}' not supported. Please report to library owner for further verification" if bcDigest.nil?

    bcDigest = eval(@config.provider_config[:bc_digest])

    # https://soatok.blog/2021/11/17/understanding-hkdf/
    # info field should be the randomness entrophy compare to salt
    # HKDf can have fix or null salt but better have additional info for each purposes
    @config.info = "" if @config.info.nil?

    logger.debug "Salt length : #{@config.salt.nil? ? "0" : @config.salt.length}"
    logger.debug "Info length : #{@config.info.nil? ? "0" : @config.info.length}"
    logger.debug "Digest : #{bcDigest}"

    logger.warn "Salt is empty!" if is_empty?(@config.salt)

    hkdf = org.bouncycastle.crypto.generators.HKDFBytesGenerator.new(bcDigest)
    hkdfParam = org.bouncycastle.crypto.params.HKDFParameters.new(to_java_bytes(input), to_java_bytes(@config.salt) ,to_java_bytes(@config.info))
    hkdf.init(hkdfParam)

    out = ::Java::byte[@config.outBitLength/8].new
    hkdf.generateBytes(out, 0, out.length)

    case output
    when :b64
      to_b64(out)
    when :hex
      to_hex(out)
    else
      out
    end

  rescue Exception => ex
    raise KDFEngineException, ex
  end
  
end