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CyberPDX Crypto 1: Encoding

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Wu-chang Feng

on 10 July 2018

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Transcript of CyberPDX Crypto 1: Encoding

Binary
Hexadecimal

CyberPDX Cryptography
Encoding

ASCII
Visual Encoders
Before we get to encryption, we need to learn encoding

Representing information in ways computers recognize
101000001
321
Which one is 321?
Code 39 Code 128 UPC

All of them
ASCII maps 1-byte values to characters
Used in URLs, Web pages, e-mail
(in decimal)
100 10 1
How did we get these?
"Base-10"
Positions denote powers of 10
Digits 0-9 denote position values
101 million and one?
(Yes), but also 321 in binary (Base-2)
101000001
256 128 64 32 16 8 4 2 1
How did we
get these?
2 2 2 2 2 2 2 2 2
"Base-2"
Places denote powers of 2
Digits 0 and 1 denote place values
8 7 6 5 4 3 2 1 0
256 + 0 + 64 + 0 + 0 + 0 + 0 + 0 + 1 = 321
Binary group activity
With a partner
1) Find the decimal values of binary numbers below
x = 1 0 0 1 1
y = 0 1 0 0 1
x-y x+y
141
0x
141 in decimal?
(Yes), but also 321 in hexadecimal (Base-16)
000101000001
0x141
256 16 1
How did we
get these?
16 16 16
"Base-16"
2 1 0
1x256 + 4x16 + 1x1 = 321
0001 0100 0001
1 4 1
Places denote powers of 16
But, requires 16 distinct digit settings to denote values
Binary 0,1
Decimal 0,1,2,3,4,5,6,7,8,9
Hexadecimal 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
0x1AF
256 16 1
1x256 + 10x16 + 15x1 = 431
0x333231
3,355,185?
(Yes), but also "321" in ASCII
0x333231
0x33 0x32 0x31
'3' '2' '1'
Collaborate to decode the full message:
ASCII group activity
Snippet #1: 54 68 65 20 68 6F 6D 65 20 74 6F
Snippet #2: 65 76 65 72 79 6F 6E 65 20 69 73
Snippet #3: 74 6F 20 68 69 6D 20 68 69 73
Snippet #4: 63 61 73 74 6C 65 20 61 6E 64
Snippet #5: 66 6F 72 74 72 65 73 73 2E
Snippet #6: 45 64 77 61 72 64 20 43 6F 6B 65
Steganography
Is 321 here?
Maybe this will help
http://crypto.cyberpdx.org/static/psu_logo.jpg
http://exif.regex.info/
http://datalab.cs.pdx.edu/unplugged/baseconversion.html
Why hexadecimal?
Recall binary
Hexadecimal activity
Cryptography challenges
Read letter carefully
PDF files on the key drive are password protected with lowercase keys found by solving challenges
Flags in capital letters found by reading the PDF files (and some thinking) to be submitted to web site ( http://crypto.cyberpdx.org/ )
One set of challenges released each day
Solve by 8:30am the following day
Test your team's accounts
Help readily given by faculty in office hours at Ondine
Install Barcode and QR code scanning software
Each team member should go through challenge solutions
May be a time your team will need you!
10 10 10
2 1 0
Code 39
3x100 + 2x10 + 1x1
2) Decimal values of
http://datalab.cs.pdx.edu/unplugged/binarycards.html
= 19
= 9
16 8 4 2 1
x-y x+y
3) Binary representation of
10 = 01010
28 = 11100
Concealing messages or information within other nonsecret text or data
x-y = 10
x+y = 28
0x0CD
256 16 1
0x256 + 12x16 + 13x1
Hexadecimal example
0 + 192 + 13 = 205
Why should we care?
Computers use binary (bits) to store all information
Humans encode characters in pairs of hexadecimal digits
Each pair of hex digits is 8 bits or 1 byte
Bytes are the smallest unit of data for computers
Is this 321?
Encode bits as bar widths
Wide=1
Narrow=0
Plus spacing
Map patterns to character set
Code 39 misapplied
QR code (Quick Response)
2D barcode
Red squares for position and alignment
Red strips identify rows, columns of bits
Green denotes data type (text, URL, etc.)
Blue is version (number of modules)
Source: http://www.ucreative.com/articles/what-is-a-qr-code-and-how-does-it-work/
QR code (Quick Response)
Data encoded directly as bits in byte-sized modules
3
2
1
Mini-race
Set of encoding puzzles that ends with a riddle.

Meant for each of you to get practice and to teach each other

Give me the answer to the riddle to get wristbands for your team
256 128 64 32 16 8 4 2 1
Keep ASCII table around for later...
Full transcript