Introduction to Cryptography with Open-Source Software

Introduction to cryptography 11

Using one-way functions

When Alice first logs onto a system, she creates a password for hers e lf.

The system applies a suitable one- way function to her password, and stores

the r e sult in a password file. Now for every successive login

1. Alice sends the system her password;

2. the system applies the one-way function to her password and compares

the r e sult with the r e sult it calculated originally;

3. if the two agree, Alice is allowed into the system.

The possibility is open for a dictio nary attack; to g e t onto the system, a

hacker (say, Mallory) need o nly compile a list of lots of possible passwords,

and try each of them. To prevent this, most computer systems add salt; this

is a random string appended to the ...