Presentation Slides
Cryptography Basics
For CTF Competitions
What is Cryptograhpy?
Secure Communication
What is a cipher?
How we get there
Common Different Representations of Text
| Base | Encoding | ASCII | Result Text | Note |
|---|---|---|---|---|
| 2 | Binary | Moon | 01001101 01101111 01101111 01101110 | Digits 0-1 |
| 8 | Octal | Magic | 115 141 147 151 143 | Digits 0-7 |
| 10 | Decimal | Sunset | 83 117 110 115 101 116 | Digits 0-9 |
| 16 | Hex | Elements | 45 6C 65 6D 65 6E 74 73 | Digits 0-9 and A-F |
| 64 | Base64 | Celestial! | Q2VsZXN0aWFsIQ== | a-z, A-Z, 0-9. = or == as padding |
There exist other representations such as Morse Code and Braille
Common Ciphers
Rail Fence Cipher
- Requires number of “rails”, with an optional offset
- el hr,hwaeyuHloTee o r o
Atbash Cipher
- Tllw, sld ziv blf?
Shift Cipher
- J bn epjoh xfmm
Vigenere Cipher
- Needs a key - “CTF”
- Ihtf mt jxft, B’r ieff
ROT13
- V ubarfgyl qba’g erzrzore jung V jebgr
Affine Cipher
- Trrk ijhf ro gwn HGQ
Substitution Cipher
- Replace a letter with another letter
- quipquip
Other
Symbols
Other Symbols
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