Hashing Algorithm: MD5

IJSRD - International Journal for Scientific Research & Development| Vol. 1, Issue 9, 2013 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 1931
Hashing Algorithm: MD5
Shweta Mishra1
Shikha Mishra2
Nilesh Kumar3
1, 2, 3
Department of Computer Science & Engineering
1
Echelon Institute of Technology, Faridabad, India 2, 3
JB Knowledge Park, Faridabad, India
Abstract—a message digest is a cryptographic hash function
containing a string of digits created by a one-way hashing
formula. Message digests are designed to protect the
integrity of a piece of data or media to detect changes and
alterations to any part of a message. In this paper, we have
explained the hashing algorithm of MD5 and also proposed
how to use it for file transmission and for hashing any
string.
General Terms: Security, Algorithms, Auxiliary Functions
Key words: Hash function, MD.
I. INTRODUCTION
Message Digest is a type of cryptography utilizing hash
values that can warn the copyright owner of any
modifications applied to their work. Message digest hash
numbers represent specific files containing the protected
works. One message digest is assigned to particular data
content. It can reference a change made deliberately or
accidentally, but it prompts the owner to identify the
modification as well as the individual(s) making the change.
Message digests are algorithmic numbers. MD5 was the last
in a succession of cryptographic hash functions designed by
Ron Rivest in the early 1990s [1].
It is a widely-used well-known 128-bit iterated
hash function, used in various applications including
SSL/TLS, IPsec, and many other cryptographic protocols. It
is also commonly-used in implementations of time stamping
mechanisms, commitment schemes, and integrity-checking
applications for online software, distributed systems, and
random-number generation.
Message digest functions are used to produce
digital summaries of information called message digests.
Message digests are commonly 128 bits to 160 bits in length
and provide a digital identifier for each digital file or
document. Message digest functions are mathematical
functions that process information to produce a different
message digest for each unique document [2]. Identical
documents have the same message digest; but if even one of
the bits for the document changes, the message digest
changes.
Because message digests are much shorter than the
data from which the digests are generated and the digests
have a finite length, duplicate message digests called
collisions can exist for different data sets. However, good
message digest functions use one-way functions to ensure
that it is mathematically and computationally infeasible to
reverse the message digest process and discover the original
data. Finding collisions for good message digest functions is
also mathematically and computationally infeasible but
possible given enough time and computational effort.
However, even if an attacker discovers a collision, it is
highly improbable that the collision could be useful.
II. NETWORK SECURITY AND MESSAGE DIGEST
Security and privacy is a growing concern in the Internet
community, due to the Internet’s rapid growth and the desire
to conduct business over it safely. This desire has led to the
advent of several proposals for security standards, such as
secure IP, Secure HTTP (SHTTP), and the Secure Socket
Layer (SSL). Thus, the need to use encryption protocols
such as DES and RSA is increasing. One problem with
using cryptographic protocols is the fact that they are slow.
An important question then is whether security can be
provided at gigabit speeds.
The standard set of algorithms required to secure a
connection includes a bulk encryption algorithm such as
DES, a cryptographic message digest such as MD5, a key
exchange algorithm such as Diffie-Hellman to securely
distribute a private key, and some form of digital signature
algorithm to authenticate the parties, such as RSA. The
encryption and hash digest algorithms must be applied to
every packet going across a link to ensure confidentiality,
and therefore the performance of these algorithms directly
affects the achievable throughput of an application. MD5 is
a message digest algorithm used for authentication and
message integrity. MD5 is a “required option” for secure IP;
by required option we mean that an application’s use of
MD5 in IP is optional, but an implementation must support
use of that option. MD5 is also the default message digest
algorithm proposed for SHTTP; and is also used in SSL.
III. MD5 ALGORITHM
The MD5 algorithm is designed to be quite fast on 32-bit
machines. In addition, the MD5 algorithm does not require
any large substitution tables; the algorithm can be coded
quite compactly. The MD5 algorithm is an extension of the
MD4 message-digest algorithm MD5 is slightly slower than
MD4, but is more "conservative" in design.
MD5 algorithm takes as input a message of
arbitrary length and produces as output a 128 bit message
digest of the input. The authentication algorithm computes a
digest of the entire data of the message, used for
authentication. Typically, the message digest is registered
with a trusted third-party, or encrypted via other means. The
digest is used by the receiver to verify the contents of a
message. It can also be used to encrypt the contents of a
message, via a second pass over the data by another
algorithm. MD5 requires that both the sender and receiver
compute the digest of the entire body of a message [3] [4].
Suppose a b-bit message as input, and that we need
to find its message digest.

(IJSRD/Vol. 1/Issue 9/2013/0060)
Step. 1 : Append padded bits--
The message is padded so that its length is
congruent to 448, modulo 512. 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.
Step. 2 : Append length--
A 64 bit representation of b is appended to the
result of the previous step. The resulting message
has a length that is an exact multiple of 512 bits.
Step. 3 : Initialize MD Buffer--
A four-word buffer (A, B, C, D) is used to compute
the message digest. Here each of A, B, C, D is a 32
bit register. These registers are initialized to the
following values in hexadecimal:
Word A: 01 23 45 67
Word B: 89 ab cd ef
Word C: fe dc ba 98
word D: 76 54 32 10
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) = XY v not(X) Z
G(X,Y,Z) = XZ v Y not(Z)
H(X,Y,Z) = X xor Y xor Z
I(X,Y,Z) = Y xor (X v not(Z))
If the bits of X, Y, and Z are independent and
unbiased, the each bit of F(X,Y,Z), G(X,Y,Z),
H(X,Y,Z), and I(X,Y,Z) will be independent and
unbiased.
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[5].
IV. MD5 HELPER FUNCTIONS
The BufferA.
MD5 uses a buffer that is made up of four words, each 32
bits long. These words are called A, B, C and D. They are
initialized as:
Fig. 1: MD5 Functions
Word A: 01 23 45 67
Word B: 89 ab cd ef
Word C: fe dc ba 98
Word D: 76 54 32 10
The TableB.
MD5 uses a table K that has 64 elements. The table is
computed beforehand to increase the speed of the
computation.
Auxiliary Functions(F)C.
MD5 uses four auxiliary functions that each take as input
three 32-bit words and produce as output one 32-bit word.
They apply the logical operators and, or, not and xor to the
input bits.
V. MD5 IN FILE TRANSMISSION
MD5 digests have been widely used in the software world to
provide some assurance that a transferred file has arrived
intact. , file servers often provide a pre-computed MD5
checksum for the files, so that a user can compare the
checksum of the downloaded file to it. However, now that it
is easy to generate MD5 collisions, it is possible for the
person who created the file to create a second file with the
same checksum, so this technique cannot protect against
some forms of malicious tampering. Also, in some cases, the
checksum cannot be trusted in which MD5 can only provide
error-checking functionality.
Hashing algorithm is applied on the file that to be
transmitted. Hashing value is then generated. When the file
is sent to the user or receiver one of the two conditions
arises. If the hash value received and the hash value
calculated matches then the file is correctly received by the
user but if those two values don’t match then the received
file have some error. In this way MD5 is used for
authentication purpose.
Fig. 2: MD5 in file transmission

(IJSRD/Vol. 1/Issue 9/2013/0060)
VI. CONCLUSION
Thus we saw that how message digest 5 is used for
authenticating any file and how it is used for hashing any
string using some helper functions. In my future work I
would be implementing this file transmission by using two
different algorithms and would like to show which one is
better by comparing their speeds and complexity. We would
also like to show how the various attacks are applied on
MD5 and what are their effects.
REFERENCES
[1] http://theory.lcs.mit.edu/~rivest/
[2] Bruce Schneir “Applied Cryptography: Protocols,
Algorithms, and Source Code in C”; 18.5 MD5 (pp.
436-441)
[3] Ronald Rivest: The MD5 Message Digest Algorithm,
RFC1321, April 1992, ftp://ftp.rfc-
editor.org/innotes/rfc1321.txt
[4] R.L. Rivest. The MD5 Message-Digest Algorithm.
RFC1321, MIT Laboratory for Computer Science and
RSA Data Security, Inc., April 1992.
[5] Amphion. CS5315, High Performance Message Digest
5 Algorithm (MD5) Core. Datasheet, URL:
http://www.amphion.com/acrobat/DS5315.pdf, (visited
September 9, 2004).
[6] J. Black, M. Cochran, T. Highland: A Study of the
MD5 Attacks: Insights and Improvements, March 3,
2006

Hashing Algorithm: MD5

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