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Cryptographic Hash Function: MD5
1
1
Md. Shahidul Islam
CSE, KU
shahid.sm35@gmail.com
Outline
 Introduction
Features
Application
Algorithm
Hash analysis
Drawbacks
2
2
Introduction
 A cryptographic hash function is a kind of algorithm
that can be run on a piece of data, like an individual
file or a password, producing a value called a
checksum.
 MD5 (Message-Digest algorithm 5) is a widely used
cryptographic hash function designed by Ronald L.
Rivest in 1991.
 It is one in a series of message digest algorithms.
3
3
Features of a hash function
 Fixed Length Output (Hash Value)
 Efficiency in computing
 Collision Resistance, two different message should not have
the same hash value
 Deterministic so the same message always results in the same
hash
 Infeasible to generate a message from its hash value except
by trying all possible messages
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4
Application
 There are two types of application of hash function:
1. Password Storage
2. Data Integrity Check
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5
Application (Cont.)
 MD5 is used to store hash passwords and verify
when user login.
 An intruder can only see the hashes of passwords,
even if he accessed the password.
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6
Application (Cont.)
7
7
Application (Cont.)
 The integrity check helps the user to detect any
changes made to original file.
8
8
Algorithm
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9
Step 1: Append padded bits:
• The message is padded so that, length mod 512 = 448
• A single “1” bit is appended to the message, and then “0” bits are
appended so that the length in bits equals 448 modulo 512.
Message 1 0 0 0 0 0
(Message length + padded bits) % 512 = 448
Algorithm (Cont.)
10
10
Step 2: Append length:
• A 64 bit integer representation of message is appended to the result of
the previous step.
• The resulting message has a length that is an exact multiple of 512
bits.
Message 1 0 0 0 0 0 64bits
(Message length + padded bits + 64 bits ) % 512 = 0
Algorithm (Cont.)
11
Step 3: Initialize MD Buffer:
• A four-word buffer (A,B,C,D) is used to compute the message digest.
• These are initialized to the
following values in hexadecimal:
A: 01 23 45 67
B: 89 ab cd ef
C: fe dc ba 98
D: 76 54 32 10
Algorithm (Cont.)
12
Step 4: Process message in 16-word blocks:
• Four auxiliary functions that take as input three 32-bit
words and produce as output one 32-bit word.
F(X, Y, Z) = (X ˄ Y) ˅ (¬ X ˄ Z)
G(X, Y, Z) = (X ˄ Z) ˅ (Y ˄ ¬ Z)
H(X, Y, Z) = X  Y  Z
I(X, Y, Z) = Y  (X ˅ ¬Z)
Algorithm (Cont.)
13
Step 5: Output:
• The message digest produced as output is A, B, C, D.
• That is, output begins with the low-order byte of A,
and end with the high-order byte of D.
A1 A2 . . . . . . . . . . . . . . . . . . . . D3
128 bits = 32 hexadecimal digits
A1, A2 are bytes
Hash analysis
14
• A small change in original message and the output
digest is completely different
Hash analysis (Cont.)
15
• Arbitrary message length to fixed length digest
• For MD5 128 bits = 32bits hexadecimal
Drawbacks
 In 1993 a hash collision was found in MD5 compression
function.
 In 2009 a preimage attack against MD5 was published that
breaks MD5’s preimage resistance.
 In 2012, the most infamous attack happened by the Flame
Malware. The CMU Software Engineering Institute considers
MD5 "cryptographically broken and unsuitable for further
use".
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16
Drawbacks (Cont.)
 For cracking password crackers use rainbow table
 Salting process can make rainbow table ineffective
17
17
Thank You
18
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Cryptographic hash function md5

  • 1. Cryptographic Hash Function: MD5 1 1 Md. Shahidul Islam CSE, KU [email protected]
  • 3. Introduction  A cryptographic hash function is a kind of algorithm that can be run on a piece of data, like an individual file or a password, producing a value called a checksum.  MD5 (Message-Digest algorithm 5) is a widely used cryptographic hash function designed by Ronald L. Rivest in 1991.  It is one in a series of message digest algorithms. 3 3
  • 4. Features of a hash function  Fixed Length Output (Hash Value)  Efficiency in computing  Collision Resistance, two different message should not have the same hash value  Deterministic so the same message always results in the same hash  Infeasible to generate a message from its hash value except by trying all possible messages 4 4
  • 5. Application  There are two types of application of hash function: 1. Password Storage 2. Data Integrity Check 5 5
  • 6. Application (Cont.)  MD5 is used to store hash passwords and verify when user login.  An intruder can only see the hashes of passwords, even if he accessed the password. 6 6
  • 8. Application (Cont.)  The integrity check helps the user to detect any changes made to original file. 8 8
  • 9. Algorithm 9 9 Step 1: Append padded bits: • The message is padded so that, length mod 512 = 448 • A single “1” bit is appended to the message, and then “0” bits are appended so that the length in bits equals 448 modulo 512. Message 1 0 0 0 0 0 (Message length + padded bits) % 512 = 448
  • 10. Algorithm (Cont.) 10 10 Step 2: Append length: • A 64 bit integer representation of message is appended to the result of the previous step. • The resulting message has a length that is an exact multiple of 512 bits. Message 1 0 0 0 0 0 64bits (Message length + padded bits + 64 bits ) % 512 = 0
  • 11. Algorithm (Cont.) 11 Step 3: Initialize MD Buffer: • A four-word buffer (A,B,C,D) is used to compute the message digest. • These are initialized to the following values in hexadecimal: A: 01 23 45 67 B: 89 ab cd ef C: fe dc ba 98 D: 76 54 32 10
  • 12. Algorithm (Cont.) 12 Step 4: Process message in 16-word blocks: • Four auxiliary functions that take as input three 32-bit words and produce as output one 32-bit word. F(X, Y, Z) = (X ˄ Y) ˅ (¬ X ˄ Z) G(X, Y, Z) = (X ˄ Z) ˅ (Y ˄ ¬ Z) H(X, Y, Z) = X  Y  Z I(X, Y, Z) = Y  (X ˅ ¬Z)
  • 13. Algorithm (Cont.) 13 Step 5: Output: • The message digest produced as output is A, B, C, D. • That is, output begins with the low-order byte of A, and end with the high-order byte of D. A1 A2 . . . . . . . . . . . . . . . . . . . . D3 128 bits = 32 hexadecimal digits A1, A2 are bytes
  • 14. Hash analysis 14 • A small change in original message and the output digest is completely different
  • 15. Hash analysis (Cont.) 15 • Arbitrary message length to fixed length digest • For MD5 128 bits = 32bits hexadecimal
  • 16. Drawbacks  In 1993 a hash collision was found in MD5 compression function.  In 2009 a preimage attack against MD5 was published that breaks MD5’s preimage resistance.  In 2012, the most infamous attack happened by the Flame Malware. The CMU Software Engineering Institute considers MD5 "cryptographically broken and unsuitable for further use". 16 16
  • 17. Drawbacks (Cont.)  For cracking password crackers use rainbow table  Salting process can make rainbow table ineffective 17 17

Editor's Notes

  • #4: A checksum is a small-sized datum derived from a block of digital data for the purpose of detecting errors. - wikipedia
  • #8: Image source: Internet
  • #9: Image source: Internet
  • #17: A preimage attack on cryptographic hash functions tries to find a message that has a specific hash value.