Encrypt-It-Rite, a vendor of encryption software, sells a symmetric cipher that uses a 56-bit key.  The company decides to conduct a “challenge” to crack an encrypted message using a brute-force approach.  The average time to crack the message is found to be2 hrs.  As a result, Encrypt-It-Rite decides to increase the key length by 8 bits, from 64 to 72 bits.  They then conduct another challenge.  What average cracking time would be expected for the new, improved cipher? If Encrypt-It-Rite would like to increase the average cracking time to at least 100 years, what will be the minimal length of the key?