MD5 ALGORITHM

By A.SHAHGHOLI AND H.R.BARZEGAR

Shahgholi_a@hotmail.com, h.r.barzegar@gmail.com

OPENING MD5 algorithm can be used as a digitalsignature mechanism. This presentation will explore thetechnical aspects of the MD5 algorithm.

DESCRIPTION OF THE MD5 ALGORITHM• Takes as input a message of arbitrary length and produces as output a 128 bit “fingerprint” or “message digest” of the input.• It is conjectured that it is computationally

infeasible to produce two messages having the same message digest.• Intended where a large file must be “compressed” in a secure manner before being encrypted with a private key under a public-key cryptosystem such as PGP.

MD5 ENCRYPT

MD5 DECRYPT

HASHUNG ALGORITHM IN C#string input = "asd";

System.Security.Cryptography.MD5 alg = System.Security.Cryptography.MD5.Create();System.Text.UTF8Encoding enc = new System.Text.UTF8Encoding();

byte[] hash = alg.ComputeHash(enc.GetBytes(input));string output = Convert.ToBase64String(hash);

// outputs:   eBVpbsvxyW5olLd5RW0zDg==Console.WriteLine(output);

IT WILL USE MD5 HASHING ALGORITHM TO GENERATE A CHECKSUM FOR FILE “C:\\LOGING.LOG”.

package com.mkyong.test;   import java.io.FileInputStream; import java.security.MessageDigest; public class MD5CheckSumExample { public static void main(String[] args)throws

Exception { MessageDigest md =

MessageDigest.getInstance("MD5"); FileInputStream fis =newFileInputStream("c:\\loging.log");  

byte[] dataBytes = new byte[1024];   int nread = 0;

while ((nread = fis.read(dataBytes)) != -1) { md.update(dataBytes, 0, nread); }; byte[] mdbytes = md.digest(); //convert the byte to hex format method 1

StringBuffer sb = new StringBuffer(); for (int i = 0; i < mdbytes.length; i++) { sb.append(Integer.toString((mdbytes[i] & 0xff) +

0x100, 16).substring(1)); }   System.out.println("Digest(in hex format):: " +

sb.toString());  

//convert the byte to hex format method 2 StringBuffer hexString = new StringBuffer(); for (int i=0;i<mdbytes.length;i++)

{ String hex=Integer.toHexString(0xff &

mdbytes[i]); if(hex.length()==1) hexString.append('0');

hexString.append(hex); } System.out.println("Digest(in hex format):: " +

hexString.toString()); } }

OUTPUT

Digest(in hex format):: e72c504dc16c8fcd2fe8c74bb492affa

Digest(in hex format):: e72c504dc16c8fcd2fe8c74bb492affa

MD5 ALGORITHM Suppose a b-bit message as input, and that we need to find its message

digest.

MD5 ALGORITHM

Step 1 – append padded bits: – The message is padded so that its length is congruent to 448, modulo 512. • Means extended to just 64 bits shy of

being of 512 bits long. – 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.

MD5 ALGORITHM• Step 2 – append length:– A 64 bit representation of b is appended

tothe result of the previous step.– The resulting message has a length that

isan exact multiple of 512 bits.

MD5 ALGORITHM • Step 3 – Initialize MD Buffer• A four-word buffer (A,B,C,D) is used tocompute the message digest.– Here each of A,B,C,D, is a 32 bit register.

MD5 ALGORITHMStep 3 cont.• These registers are initialized to thefollowing values in hexadecimal:word A: 01 23 45 67word B: 89 ab cd efword C: fe dc ba 98word D: 76 54 32 10

MD5 ALGORITHM• Step 4 – Process message in 16-word

blocks.– Four auxiliary functions that take as

inputthree 32-bitwords and produce as output one 32-bit

word.F(X,Y,Z) = XY v not(X) ZG(X,Y,Z) = XZ v Y not(Z)H(X,Y,Z) = X xor Y xor ZI(X,Y,Z) = Y xor (X v not(Z))

MD5 ALGORITHM• Step 4 – Process message in 16-wordblocks cont.– if the bits of X, Y, and Z are independent

andunbiased, the each bit of F(X,Y,Z),

G(X,Y,Z),H(X,Y,Z), and I(X,Y,Z) will be independentand unbiased.

MD5 ALGORITHM• Step 5 – output– The message digest produced as output

isA, B, C, D.– That is, output begins with the low-orderbyteof A, and end with the high-order byte of

D.

MD5 PSEUDO CODE: //Note: All variables are unsigned 32 bits

and wrap modulo 2^32 when calculating var int[64] r, k  //r specifies the per-round shift amounts r[ 0..15] := {7, 12, 17, 22, 7, 12, 17, 22, 7,

12, 17, 22, 7, 12, 17, 22} r[16..31] := {5, 9, 14, 20, 5, 9, 14, 20, 5,

9, 14, 20, 5, 9, 14, 20} r[32..47] := {4, 11, 16, 23, 4, 11, 16, 23, 4,

11, 16, 23, 4, 11, 16, 23} r[48..63] := {6, 10, 15, 21, 6, 10, 15, 21, 6,

10, 15, 21, 6, 10, 15, 21} 

//Use binary integer part of the sines of integers (Radians) as constants:

for i from 0 to 63 k[i] := floor(abs(sin(i + 1)) × (2 pow 32))end for

 //Initialize variables: var int h0 := 0x67452301 var int h1 := 0xEFCDAB89 var int h2 := 0x98BADCFE var int h3 := 0x10325476 

//Pre-processing: append "1" bit to messageappend "0"

bits until message length in bits ≡ 448 (mod 512)append length to message

/* bit (not byte) length of unpadded message as 64-bit little-endian integer */

 //Process the message in successive 512-bit chunks:for each 512-bit chunk of message break chunk into sixteen 32-bit little-endian words w[j], 0 ≤ j ≤ 15

//Initialize hash value for this chunk: var int a := h0 var int b := h1 var int c := h2 var int d := h3

//Main loop: for i from 0 to 63 if 0 ≤ i ≤ 15 then f := (b and c) or ((not b) and d) g := i else if 16 ≤ i ≤ 31 f := (d and b) or ((not d) and c) g := (5×i + 1) mod 16 else if 32 ≤ i ≤ 47 f := b xor c xor d g := (3×i + 5) mod 16 else if 48 ≤ i ≤ 63 f := c xor (b or (not d)) g := (7×i) mod 16 temp := d d := c c := b b := b + leftrotate((a + f + k[i] + w[g]) , r[i]) a := temp end for

//Add this chunk's hash to result so far: h0 := h0 + a h1 := h1 + b h2 := h2 + c h3 := h3 + d end for  var char digest[16] := h0 append h1

append h2 append h3 //(expressed as little-endian)

 //leftrotate function definition leftrotate (x, c) return (x << c) or (x >> (32-c)); 

MD5 CODE WITH JAVA:

package javaapplicationMD5; import java.security.*; class Md5 { public static void main(String[] a) { try { MessageDigest md =

MessageDigest.getInstance("MD5"); System.out.println("Message digest object info: ");

System.out.println(" Algorithm = "+md.getAlgorithm());

System.out.println(" Provider = "+md.getProvider());

System.out.println(" toString = "+md.toString()); 

String input = ""; md.update(input.getBytes());

byte[] output = md.digest(); System.out.println(); System.out.println("MD5(\""+input+"\") ="); System.out.println(" "+bytesToHex(output)); 

input = "abc"; md.update(input.getBytes());

output = md.digest(); System.out.println(); System.out.println("MD5(\""+input+"\") ="); System.out.println(" "+bytesToHex(output));

input = "abcdefghijklmnopqrstuvwxyz"; md.update(input.getBytes());

output = md.digest(); System.out.println();

System.out.println("MD5(\""+input+"\") ="); System.out.println(" "+bytesToHex(output));  

} catch (Exception e) { System.out.println("Exception: "+e); } } public static String

bytesToHex(byte[] b) { char hexDigit[] = {'0', '1', '2', '3', '4',

'5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};

StringBuffer buf = new StringBuffer(); for (int j=0; j<b.length; j++)

{ buf.append(hexDigit[(b[j] >> 4) & 0x0f]);

buf.append(hexDigit[b[j] & 0x0f]); }

return buf.toString(); }}

SUMMARY• The MD5 algorithm is simple toimplement, and provides a “fingerprint”

ormessage digest of a message of arbitrarylength.• The difficulty of coming up with twomessages with the same message digestis on the order of 2^64 operations