The document explains secure hashing techniques, describing how hash functions transform variable-length data into fixed-length hash values that are difficult to reverse-engineer. It discusses one-way hashing, message digest functions, and specific secure hashing algorithms like SHA-0, SHA-1, and SHA-2, highlighting their characteristics and vulnerabilities. Applications of secure hashing are mentioned in contexts where sensitive data is handled, such as online banking and e-learning.

1. SECURE HASHING TECHNIQUES
By
UdhayyaGethan.M
311511205309

2. SECURE HASHING
• What ?
• Why ?
• How ?

3. What is Hashing
• A hash function is any algorithm that maps data of
variable length of data to a fixed length.
• The values returned by the hash functions are called
as hash codes, hash sums, message digest or simply
hashes.
• Hashing mostly takes a string as an input and gives
the output or the hashed values as a numerical value
mostly as an hexadecimal number.

4. What is so special about Secure
Hashing
• Hash values produced by some hash techniques can
be re hashed.
• That means we can get the original data from the
hash values.
• But hash values of secure hash techniques cant be rehashed.
• That’s why it is called as one way hashing.

5. Message Digest Functions:
• Checksums  fingerprint of a message
• If message changes, checksum will not match
• Most checksums are good in detecting
accidental changes made to a message
• They are not designed to prevent an adversary
from intentionally changing a message resulting a
message with the same checksum
• Message digests are designed to protect against
this possibility

6. One-Way Hash Functions:
Example
• M = “Elvis”
• H(M) = (“E” + “L” + “V” + “I” + “S”) mod 26
• H(M) = (5 + 12 + 22 + 9 + 19) mod 26
• H(M) = 67 mod 26
• H(M) = 15

7. Collision:
Example
• x = “Viva”
• Y = “Vegas”
• H(x) = H(y) = 2

8. Criteria's for a hash function:
• Given M,
• it is easy to compute h
• Given any h,
• it is hard to find any M such that H(M) = h
• Given M1, it is difficult to find M2
• such that H(M1) = H(M2)
• Functions that satisfy these criteria are called
message digest
• They produce a fixed-length digest (fingerprint)

9. Secure Hashing Algorithm (SHA) :
• SHA-0
• SHA-1
• SHA-2
1993
1995
2002
• SHA-224, SHA-256, SHA-384, SHA-512
SHA-1
A message
composed
of b bits
9
160-bit
message
digest

10. Steps for hashing:
•
•
•
•
•
Padding
Dividing
Computing
Initialize
Looping

11. Example for Padding:

12. Example :
• M = 01100010 11001010 1001 (20 bits)
• Padding is done by appending to the input
– A single bit, 1
– 427 0s
– A 64-bit integer representing 20
• Pad(M) = 01100010 11001010 10011000 …
00010100

13. Example :
• Length of M = 500 bits
• Padding is done by appending to the input:
– A single bit, 1
– 459 0s
– A 64-bit integer representing 500
• Length of Pad(M) = 1024 bits

14. Comparison:
Output
size
(bits)
Internal Block
Max
Word
state size size message size Rounds Operations
(bits)
(bits) size (bits) (bits)
Collisions
found
SHA-0
160
160
512
264 − 1
32
80
+, and, or,
xor, rot
Yes
SHA-1
160
160
512
264 − 1
32
80
+, and, or,
xor, rot
None
(252 attack)
256/224
256
512
264 − 1
32
64
+, and, or,
xor, shr, rot
None
512/384
512
1024
2128 − 1
64
80
+, and, or,
xor, shr, rot
None
SHA-2

15. Some facts you must know:
• Sha-512 is illegal to use in some countries.
• Because it is tough even to the government to
crack a 512 bit encryption.
• Sha-0 and Sha-1 are very much prone to
collision of data's.
• Md5 hashing technique is no longer secure.
• Md5 has been compromised.
• It has a hash table about the size of 64Gb.

16. Applications of Secure Hashing:
•
•
•
•
•
Online Banking
Online Shopping
E-Learning
Web servers
………
In short, wherever sensitive data's are
handled and wherever you need to log yourself
in to access data secure hashing is used there.

17. Thank you