Encryption LAB

If you have a lab from earlier which has not been finished, and most of you do, work on earlier labs first.

Answer as many questions as you can in two hours.

Assume a simple cipher, which encodes only the 26 letters of the alphabet, and adds N (mod 26) to each character to encode, and subtracts N (mod 26) to decode..
How would you crack such a code?
How much effort would that be? (Give O(N) if you can)

Assume a simple cipher, with a scrambled table for substitutions.
Assume a fairly large text file. You have only the coded file.
How would you crack such a code?
How much effort would that be? (Give O(N) if you can)

Solve at least one cryptoquote.  At the end of this file is one I created at http://www.wordles.com/getmycrypto.aspx
 https://api.razzlepuzzles.com/cryptogram

One of my favorite encryption algorithms involves XOR.
Assume you know that every letter in a file was XORed with the same 8 bit pattern.
How would you crack such a code?
How much effort would that be? (Give O(N) if you can)

Assume a repeating pattern code.  (For example, the pattern of encoding repeats every 7th character.)
How would you crack such a code?
How much effort would that be? (Give O(N) if you can)

Assume two factor authentications by email.
How would you crack such a code?
How much effort would that be? (Give O(N) if you can)

Assume a web page which locks after 5 incorrect passwords in a row.
How would you crack such a code?
How much effort would that be? (Give O(N) if you can)

Assume RSA encryption with 50-digit primes.
You are given a large series of encoded packets.
How would you crack such a code?
How much effort would that be? (Give O(N) if you can)

You are a corporation. You wish to have a reasonably secure and reasonably easy encryption algorithm for sending email back and forth to clients.  Describe how you would go about choosing an approach.

Cryptoquote for you:
LT BTQTDEAV MQ IDEVITDMSR, PQH SGPQFWAU MQ PHOTDVMSR. LT CEDSGR EW SGT SDAVS EW SGR QTMBGLED, PQH UEEF AIEQ GMJ CMSG P LDMBGS PQH WDMTQHUR WPYT. LT P SDTPVADT SE SGT IEED, PQ PHJEQMVGTD SE SGT DMYG, PQ PQVCTDTD EW SGT YDR EW SGT QTTHR, P IDTVTDOTD EW SGT