One-way encryption

1. One-way encryption Follow-up on distributed processing. Follow-up on encryption. Client-side versus server side Homework: postings, talks, comments

2. Distributed processing Strategies for doing • sorting of known set of values (e.g., card deck) • sorting of unknown set of values • encrypting message • Is this embarrassingly parallel?

3. Status • You can make your weekly posting on encryption. • More guest lecturers coming. • Readings: • Check out moodle for chapter 10 on databases. This will be useful for today! • There will be a paper on AI.

4. Follow-up from talk • Summarize? • Comment?

5. mod • JavaScript and Processing each use % for the mod (aka modulo) operator • You can think of it as remainder • 10 % 5 => 0 • 100 % 10 => 0 • 101 % 10 => 1 • 5 % 10 => 5 • ???

6. Uses of mod • Slide show • Wrap around screen • Computing change • Checking if one number is divisible by another • ?

7. My summary • Pick 2 very big primes (each at least 300 digits) p and q • Compute n = p*q • Compute (n) = (p-1)* (q-1) • Choose e such that gcd(e, (n) ) is 1 (meaning no common divisors) • Compute d such that d*e = 1 mod ((n) ) • Public key is (e, n) • Private key is (d,n)

8. Bits and bytes • Bit is 0 or 1 • Bit stands for binary digit • Byte is 8 bits

9. Is a picture worth a 1000 words? • Assume straight encoding of picture in which each pixel element is • black or white for how many bits? • one of 256 different colors (i.e., reference to a pallette) for how many bits? • 0 to 255 levels of Red, 0 to 255 levels of Green, 0 to 255 levels of Blue for how many bits?

10. Is a picture…, cont. • How big is the picture? • How many pixels wide and how many high?

11. How much space is taken up by 1000 words? • Standard ASCII encoding is 8 bits for 1 byte for character. • What would be reasonable estimate for a word? • word plus space?

12. Do computations!

13. Image encodings • Good topic for presentation • lossless means that the full original can be restored • gif is lossless • lossy means that it cannot • jpeg is lossy

14. Redundancy in messages • In some sense, the opposite of steganography and cryptography • Make a message longer so receiver can check if message is correct. • Send extra information. • Ultimate form: send the whole message twice. • Receiver can detect a problem and request new transmission.

15. Check bit, parity bit • Using a 7 bit encoding, • Decide between even or odd parity. Say odd • Send 8 bits, when the 8th bit makes it be an odd number of bits0000010 would be expanded to 000001000101011 would be expanded to 01010111

16. check digit • Various methods • One: compute sum of digits of message and compute modulo 10 and make this be the extra digit sent • Alternative (that can catch transpositions of numbers) Give weighting to numbers, compute the sum module 10 and make this be extra digit sent

17. ISBN-10 http://en.wikipedia.org/wiki/Check_digit • Uses modulo 11. Weights positions 1, 2, ….10. Computes sum modulo 11 • and adds 0, 1, 2, …, X to message.

18. Today • one-way encryption meaning no attempt to decode • Typical use is passwords!

19. Passwords • What does using input type="password" do?

20. My term • over the shoulder security • password still sent over the web. • A secure connection means that it will be encrypted and then decrypted.

21. One-way encryption • Typical use: take password and immediately encrypt it using one-way encryption and store the encrypted form. • Your program makes sure that the plaintext is the only way… • Protects against inside jobs! • Other uses???

22. SHA256 function • One of several possibilities • aka 'hash' or 'digest'. • http://www.webtoolkit.info/javascript-sha256.html

23. Where to do this? • One choice is to do this on the client, that is, using JavaScript and send it (along with other information) to the server (the middleware program = the php program) • Client side (HTML & JavaScript) • or other languages • Server side (php and also MySql) • OR other languages…

24. HTML form handling • onSubmit indicates program done immediately on the client • action indicates program on the server • So, this example does work on client and then on server • Note: in the book chapter, I use a table to format the form.

25. HTML <form name="f" action="completereg.php" onSubmit="return encode();" method="post"> User id (email address) <input type="email" name="un" required /> Password <input type="password" name="pw" required /> Confirm password <input type="password" name="cpw" required/> <input type="submit" value="Register"/> </form>

26. Notice • use of input type="password" • Notice typical device of having user/customer/client/…. enter password twice. • SOME HTML5 implementations will check that any input field that has the required attribute have a value. My code also checks.

27. The encode function • checks if user name and password entered • checks if two passwords match • if both true, invokes the SHA256 function to produce the digest and returns true • else returns false, and so action is not taken.

28. function encode() { var pw1 = document.f.pw.value; if ((document.f.un.value.length<1) ||(pw1.length<1)) { alert("Need to enter User Name and Password. Please try again."); return false; } else if (pw1 == document.f.cpw.value) {document.f.pw.value = SHA256(pw1); document.f.cpw.value = document.f.pw.value; return true; } else { alert("passwords do not match. Please try again."); return false; } }

29. Discussion and possible posting • How can this be done using cloud computing? That is, cloud computing to all the computation on server computers… • simple answer: start authentication on the client. • Research security, authentication, passwords, etc. on cloud computing

30. Homework • Review chapter 10 • Read AI article • Read about visualizations • Read about duolingo • Be prepared for next guest speakers