Lecture Date: Monday 9 February
What is encryption?
- Change the form of data to conceal the meaning
- hidden text
Why do we care? Why in CS?
- Data Security
- Do not want people to snoop on us
- Do want to know we are talking to a particular person
- plaintext - what we are hiding
- ciphertext - what it looks like after we hide it
- encrypt - go from plaintext to ciphertext
- decrypt - go from ciphertext to plaintext
- cipher - a technique for encrypting/decrypting
- key - which variant of the cipher we are using
charat that index (starting at 0)
s.length()-> how many
chars there are
s += "w"-> add a w to the end of
s is a
String. What is the index of the last
Can I post all of the code?
Yes, I will after class (probably around 1:15pm)
How do I change all variables at once
Why single quotes in if statement
to be char values, not variables or Strings
What about words that have op?
[s]topop => s
s[t]opop => st
st[opo]p => sto
stopo[p] => stop
Ceasar adds 3 to each letter (
(char)('a' + 3) yields
'd'). 3 is the “key”.
Vignere adds a different digit to each letter; key is a several-digit number. For example, with the key 1602, “programming” becomes