Method: RepoInternal::MyAES.is_string_encrypted

Defined in:

lib/lenc/aes.rb

.is_string_encrypted(key, test_str) ⇒ Object

Determines if a string is the start of an encrypted sequence

Returns true iff the start of the string seems to decrypt correctly for the given password

Parameters:

• key —

  password to use (string)

• test_str —

  the string to test

# File 'lib/lenc/aes.rb', line 440

def self.is_string_encrypted(key, test_str) 
  db = warndb  0
  
  !db || hex_dump(test_str, "is_string_encrypted?")
  
  simple_str(test_str)
  
  lnth = test_str.size
  lnth -= NONCE_SIZE_SMALL
  if lnth < AES_BLOCK_SIZE || lnth % AES_BLOCK_SIZE != 0
    !db || pr("  bad # bytes\n")
    return false
  end
  
  hdr_size = AES_BLOCK_SIZE
  
  # This method is failing, I suspect because with the mode of AES we're using (CRC?) we can't
  # decrypt only a single block, and must instead decrypt a complete chunk.
  
  # No, now I think it's interpreting a bad 'padding' value (due to only decrypting partially)
  # as indication of bad decryption
  
  if false
    warn("using full chunk size")
    hdr_size = [lnth,CHUNK_SIZE_ENCR].min
  end
  
  begin
      de = MyAES.new(false, key)  
      
      # Put this decryptor into prefix mode, so that we are only interested
      # in whether the header verifies correctly
      de.prefix_mode = true
           
      de.finish(test_str[0...hdr_size + NONCE_SIZE_SMALL])
      de.flush()
  rescue LEnc::DecryptionError => e
    !db || pr(" (caught DecryptionError #{e})\n")
    return false
  end
    
  true
end