Cryptographic hash functions are one of the most important primitives in cryptography. They are used in many applications, including digital signature schemes, MAC algorithms, and PRNG.

1. Cryptographic Attack

2. Attacks and Analysis
Submitted By :
Md. Iftekhar Alam Efat
Lecturer
IIT , NSTU
Presented By :
Al Jaber (ASH1825029M)
Saifur Rahman(ASH1825031M)
Nadim Bhuiyan (ASH1825034M)

3. Contents
• Theme
• Literature Review
• Model

4. Introduction
 Cryptographic hash functions are one of the most important primitives in cryptography.
They are used in many applications, including digital signature schemes, MAC
algorithms, and PRNG.
 A hash function takes in arbitrary length of message and produces a fixed length output
called as the message digest. A hash function should follow the following properties.
(i) It is impossible to produce the message given the hash value.
(ii)No two messages should produce the same hash output(collision resistant).
(iii)It is impossible to modify the message without modifying the hash.
 Several types of Cryptographic hash functions are used :
 Grøstl
 SHA-1
 SHA-3

5. Literature Review
 Many cryptographic hash functions are use in many application such as digital
signature ,password etc. The discovery of the collision attacks on NIST’s
standard hash function SHA-1 , there is a strong need for a secure and
efficient hash function. In 2008, NIST launched the SHA-3 competition , in
2012. To analyze AES-type functions, several cryptanalytic techniques were
developed. In there they use the start-from-the-middle and the Super-Sbox
variants of the rebound technique to analyze the reduced-round Grøstl-224
and Grøstl-256 hash functions, compression function, and permutations.

6. A Short Description of Grøstl
 Grøstl is a cryptographic hash function. It uses the same S-box as AES in a custom
construction.
 The chaining values are 512-bit for Grøstl-224 and -256. They are stored as an 8 by 8
matrix whose elements are bytes.
 The compression function takes a 512-bit chaining value (CV) and a 512-bit message
block as inputs and generates a new 512-bit CV. The compression function uses two
permutations P and Q, with input length 512-bit.
x = CompGrøstl(y, z) = P(y ⊕ z) ⊕ Q(z) ⊕ y,
 A message is padded and divided into 512-bit message blocks m1, . . .,mb and processed
as follows to generate a hash value h, hi = f(hi−1, mi).
 The final output is (512 or 1024 bits).

7. SHA-1,Rebound ATTack
 SHA-1 is a cryptographic hash function which takes an input and produces a
160-bit (20-byte) hash value known as a message digest – typically rendered
as a hexadecimal number, 40 digits long.
 The rebound attack is a tool in the cryptanalysis of cryptographic hash
functions. It was conceived to attack AES like functions such
as Whirlpool and Grøstl. The Rebound Attack is a type of statistical attack
on hash functions, using techniques such as rotational and differential
cryptanalysis to find collisions

8. Pros & Cons
 Pros :
 making it harder for an attacker to break passwords
 making it harder for an attacker to digital signature
 making it harder for an attacker to verification code
 Cons :

9. Conclusion
We analyzed the Grøstl hash functions:
Using the start-from-the middle rebound technique, we have shown a collision attack on the
Grøstl-256 hash function reduced to 5 rounds and 6 rounds with 248 and 2112 time
complexities.
Furthermore, semi-free-start collision attacks on the Grøstl- 224 and -256 hash functions
reduced to 7 rounds, on the Grøstl-224 and -256 compression functions reduced to 8 rounds
were shown and some improvements of distinguishers of the permutations were presented.
While our analysis shows (semi-free-start) collision attacks for up to seven rounds which
leaves just three rounds of security margin, it does not pose a direct threat to the full Grøstl
hash or compression function.

10. Hull Click Human Identification Protocol
 This protocol is mainly about identification of human using
Convex Hull Algorithm.
 Using Convex Hull Algorithm, Human identification can be
collected.

11. Convex Hull Algorithm
 Mainly convex hull algorithm is about
some random points within a
exact area which is a polygon.
but specialty is the inner
angles wont be more a 180
degree.
 And the are must cover all the
other points.
 Using this algorithm human’s face or finger prints are detected.
face becomes divided into some points like, distance among eyes, nose, mouth or other
things.


12. Human identification protocol
CHC protocol
 C is the computer or the server that will detect the identification.
 H is the human, who is to be identified.
 C then repeats the process and accepts or rejects.
 Let there are n=30, m=25
Secret icons or labels are = {7, 15, 27, 30}

13. Attack-01
 The possibility of of getting secret label is:
 The possibility of getting non-secret labels is:

14. Cont…
 Simulation results for Attack 01 is like below:

15. Cont…
 Output of attacks 02..