to cool things off a bit :)
Comments Off
1. /etc/shadow
On linux system user information are stored in /etc/passwd. This file is world-readable (readable by any user of the computer system, even nobody) So it purchase microsoft project 2007 is not a good idea to keep user passwords in it, even encrypted password.
The need to store (encrypted) password introduces the shadow file, which is /etc/shadow. It contains the purchase microsoft project 2007 password which has been encrypted with the salt, which is also in the purchase microsoft project 2007 shadow file.
contain of shadow file could be as follow:
luana:$1$TaORQ38u$Mfaih1b244CcesjU7Sj2T1:13975:0:99999:7:::
here, luana is the username
$1$ indicates we’re using a salt (TaORQ38u) and md5sum is being used to encrypt the key, $ signifies the beginning of the encrypted password (Mfaih1b244CcesjU7Sj2T1) and ends before :
2. Salt
salt is a string, publicly available (if you can see encrypted passwords you can see the salt), used to purchase microsoft project 2007 help with the password encryption process. Since encryption is a on-to function (or a surjection - see http://mathworld.wolfram.com/Surjection.html) two of the purchase microsoft project 2007 same words will encrypt to the same ciphertext. This means on a purchase microsoft project 2007 system with very large amount of user there will be a purchase microsoft project 2007 chance someone will use some very bad passwords (like “password” etc) and it will shows as two identical ciphertext in the shadow file.
Salt is purchase microsoft project 2007 mostly unique to each user. It is often the encryption of the purchase microsoft project 2007 time the user is added to the system (thus relatively unique for each user). This salt is purchase microsoft project 2007 mixed with the user password before we start the encryption. This means for purchase microsoft project 2007 any given two users it is extremely unlikely that they are purchase microsoft project 2007 BOTH added to the system at the same time and use the purchase microsoft project 2007 same password.
Simply put, salts allow the purchase microsoft project 2007 system to afford users to use the same passwords without having two identical encrypted passwords in its password file.
3. Note about writing programs on linux that uses crypt()
crypt is standard to most c/c++ compilers on linux system. This means you don’t even have to do #include <> in your program to use these functions.
Example program:
#include <iostream>
int main()
{
std::cout<<crypt(”kccL;pw_d:”,”$1$TMVRB39B”);
return 0;
}
When compiled on linux system (with GNU cryptography library installed) you would run:
[lubox@neo 3]$ g++ hw3.cpp -o o -lcrypt
Notice the purchase microsoft project 2007 -lcrypt option at the end. This will tell the compiler that purchase microsoft project 2007 you are using crypt function.
The above program when run will yield output:
$1$TMVRB39B$PUaDAsZctLWtj0kteqvBe1
with the purchase microsoft project 2007 salt the same, and the password is encrypted into the preceding bold part.
4. …
