class HexaPDF::Encryption::RubyARC4

See: PDF2.0 s7.6.3
For reference: This implementation is about 250 times slower than the FastARC4 version.
FastARC4 class based on OpenSSL should be used when possible.
Since this algorithm is implemented in pure Ruby, it is not very fast. Therefore the
Pure Ruby implementation of the general encryption algorithm ARC4.

def initialize(key)

Creates a new ARC4 object using the given encryption key. 
def initialize(key)
  initialize_state(key)
  @i = @j = 0
end

def initialize_state(key)

Performs the key-scheduling algorithm to initialize the state. 
def initialize_state(key)
  i = j = 0
  @state = INITIAL_STATE.dup
  key_length = key.length
  while i < 256
    j = (j + @state[i] + key.getbyte(i % key_length)) % 256
    @state[i], @state[j] = @state[j], @state[i]
    i += 1
  end
end

def process(data)

decryption.
Since this is a symmetric algorithm, the same method can be used for encryption and

Processes the given data. 
def process(data)
  result = data.dup.force_encoding(Encoding::BINARY)
  di = 0
  while di < result.length
    @i = (@i + 1) % 256
    @j = (@j + @state[@i]) % 256
    @state[@i], @state[@j] = @state[@j], @state[@i]
    result.setbyte(di, result.getbyte(di) ^ @state[(@state[@i] + @state[@j]) % 256])
    di += 1
  end
  result
end