Check Email Header for Genuineness

1. When you are suspicious about an email check the email header. most email providers give this facility under name "Show original " (gmail). in this view you can see the raw email message in its low level format

2. There are number of details in this header, but what we are interested in is the "received from " tag
there are multiple "received from " lines. which indicates the name and addresses of the mail servers through which the email passed before it reached your mailbox.

3. The last "received from " line indicates the actual origin of the mail.

consider the following email i got from moneycontrol

---------------------------------------------------------

Delivered-To: abhiapsunde@gmail.com
Received: by 10.150.50.4 with SMTP id x4cs102347ybx;
      Wed, 6 May 2009 22:30:39 -0700 (PDT)
Received: by 10.114.182.1 with SMTP id e1mr1990868waf.163.1241674239169;
      Wed, 06 May 2009 22:30:39 -0700 (PDT)
Return-Path: 
Received: from alertsmails11.moneycontrol.com (alertmails6.moneycontrol.com [124.153.78.87])
      by mx.google.com with ESMTP id q18si1743680pog.5.2009.05.06.22.30.37;
      Wed, 06 May 2009 22:30:38 -0700 (PDT)

-----------------------------------------------------

This header suggests that this email originates from alertmails6.moneycontrol.com
this is sub domain of legitimate sender moneycontrol.com and thus a genuine mail.

4.Thus if the server address in last "Received from" and the from address appearing in the mail is not same the mail is fake

RSA algorithm in C language ..

This is RSA algorithm for public key cryptography in C language

1. Prime numbers are generated using C pseudo-random generator

2. Exponentiation is replaced with simple multiplication so even larger numbers can be calculated to mod within limits of integer [ 2Byte in Turbo C/C++ compiler i used)
-------------------------------------
#include<conio.h>
#include<stdio.h>
#include<string.h>
#include<time.h>

int d,e,n;
int GenPrime(int seed);
int GenCoPrime(int num);
int IsPrime(int num);
int findD(int m,int e);
int GenKeys();
int mod(int,int,int);

int main()
{ int i,j;
char plain[50];
int cipher[50];
int len;
time_t t;
srand((unsigned) time(&t));

clrscr();
GenKeys();
printf("\nEnter some text...\n");
gets(plain);
len=strlen(plain);

printf("\n Cipher.........\n");
for(i=0;i<len;i++)
{
cipher[i]=mod(plain[i],e,n);
printf("%c",cipher[i]);
}

printf("\n decrypted.........\n");
for(i=0;i<len;i++)
{
j=mod(cipher[i],d,n);
printf("%c",j);
}


getch();

return 0;
}
int mod(int base,int expo,int div)
{
long rem=1;
int i;

for(i=0;i<expo;i++)
{
rem=(rem*base)%div;

}
return (int)rem;

}
int GenKeys()
{
int p,q,m;
int tt1;
p=GenPrime(11);
q=GenPrime(10);
n=p*q;
printf("\n P=%d , Q=%d , n=%d",p,q,n);
m=(p-1)*(q-1);
printf("\n m=%d ",m);
e=GenCoPrime(m);
printf("\n e=%d ",e);
d=findD(m,e);
printf("\n d=%d ",d);

printf("\n Private key = {%d, %d} ",d,n);
printf("\n Public key = {%d, %d} ",e,n);

return 1;
}
int GenPrime(int seed)
{
int i,tmp;

for(i=seed;;i++)
{
if(IsPrime(tmp=i+1))
{
if(rand()%2)
return tmp;
}

if(IsPrime(tmp=i+3))
{
if(rand()%2)
return tmp;
}

if(IsPrime(tmp=i+7))
{
if(rand()%2)
return tmp;
}

if(IsPrime(tmp=i+9))
{
if(rand()%2)
return tmp;
}
}

}

int IsPrime(int num)
{ int i;
if(num==2 | num==3 | num ==5 | num==7 )
return 1;
else
{
for(i=2;i<num;i++)
{
if(num%i==0)
return 0;
}
if(i==num)
return 1;
else
return 0;
}
}

int GenCoPrime(int num)
{
int i;
for(i=2;i<num;i++)
{
if(num%i != 0)
return i;
}
return 0;
}

int findD(int m,int e)
{
int i;
int d,tmp;
for(i=0;i<32767;i++)
{
tmp=1+(i*m);
if(tmp%e==0)
return tmp/e;
}
return 0;
}