Assume a password consists of 8 letters, where each letter is encoded by the ascii scheme (7 bits per character, i. e. 128 possible characters). what is the size of the key space which can be constructed by such passwords?

72,057,594,037,927,936 or 7.20576 x 10^16. Since each character can have 128 different values and there are 8 characters in the password, the number of possible passwords using that scheme is 128^8 which is 72,057,594,037,927,936 which is approximately 7.20576 x 10^16