1.
κρυπτογράφηση
Onur Şahindur

2.
Kerckhoffs’ Principle (1883)
Security should not rely on the secrecy of the algorithm; everything may be known but
the key.

3.
Historical Examples

4.
Shift Cipher (Caesar)
Brute Force
Frequency Analysis

5.
Substution Cipher
Frequency Analysis

6.
Vernam Cipher
“Perfect Secrecy”
Long Key Size
Not enough randomness

7.
Block CiphersStream Ciphers
Cryptography

8.
Substitution-Permutation (SP) Networks

9.
Lucifer v0

10.
S = {0, 1, 2, …., E, F}
For 4x4 block size, there is (24)! possibilities

11.
DES (Data Encryption Standard)
Key Analysis

12.
DES (Data Encryption Standard)
Round Boxes

13.
DES (Data Encryption Standard)
Key Generation

14.
AES (Advanced Encryption Standard)
Also known as Rijndael (Vincent Rijmen and Joan Daemen)

15.
AES (Advanced Encryption Standard)
Rounds

16.
AES (Advanced Encryption Standard)
Encryption-Decryption

17.
AES (Advanced Encryption Standard)
Cracked!
2011

18.
AES (Advanced Encryption Standard)
Which one we will use?
https://crypto.stackexchange.com/questions/5118/is-aes-256-weaker-than-192-and-128-bit-versions
*
*

19.
Modes of Operations
• Electronic Codebook (ECB)
• Cipher Block Chaining (CBC)
• Output Feedback (OFB)
• Cipher Feedback (CFB)
• Counter (CTR)

20.
Modes of Operations
ECB

21.
Modes of Operations
CBC

22.
Modes of Operations
OFB

23.
Modes of Operations
CFB

24.
Modes of Operations
CTR

25.
Cryptographic Hash Functions

26.
Public Key Cryptography

27.
DH Key Exchange

28.
RSA

29.
Key Distribution Attacks

30.
SSL/TLS

31.
• CAs’ public key should be distributed in a trusted way to
all the parties in the system in advance.
• In SSL, root CAs are approved by the browser (or the
OS) makers, and distributed with the browser/OS code.
• CAs must satisfy certain criteria for this:
– https://wiki.mozilla.org/CA:How_to_apply
– http://www.chromium.org/Home/chromiumsecurity/root-ca-policy
– http://technet.microsoft.com/enus/library/cc751157.aspx
CA (Certification Authorities)

32.
JSON Web Token (JWT)

33.
eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.
eyJ3b3JrZXJfaWQiOjI3MDg1Mn0.
KxGQ80mEpri44ruoI9kDf37qV7vgvum7miG-
HbYKtYMtG8d3JanJD8qS6alRvHbBZ2KPBEAUxlZJUMmt7X02CyEuj7XE7R
9rUIo5GhDU1UDesk2VUce6q4qaNoidlMrMxA1cSb3ijr9EIMcH7Z1tolbouah
wwIylXrKkO5_xsZuY-Y6EsLvryC3U7zKrtOu-12XO6_bCqS1r-fpijyl2aQJef-
f0SkuArtHEpLN34GSpNVJ4399QviLFndVpr81yGzeFbfDi_WILCqX9GNnrBM
6lcNxWGpk5NRTpv6aLQvMIWAO2EmHFaxFI6xxLz7qbxlnWirnalSZVwyUzH
PscoQ
Header
Payload
Signature
{
"alg": "HS256",
"typ": "JWT"
}
{
"sub": "1234567890",
"name": "John Doe",
"admin": true
}
HMACSHA256(
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
secret)

34.
0b34411749b07b1c468130c3dfa85883b
05ade9866996dd875b89190caa45a86
?