CSCI6268L33 - Foundations of Network and Computer Security...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Foundations of Network and Foundations of Network and Computer Security Computer Security J J ohn Black Lecture #33 Nov 30 th 2009 CSCI 6268/TLEN 5550, Fall 2009
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The View from Here Today is Nov 30 th ; normal lecture No Class on Weds I’m out of town and couldn’t find a replacement We will have 4 more classes after today One will be a final review
Background image of page 2
Project #2 Postponing due date until Dec 11 th There won’t be a 4 th project due to various factors You should have received 2 test messages from me One with a valid sig, one with an invalid sig These are from jrblack@cs.colorado.edu in our cert table; do NOT use the CA as the sender
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Project #2 cont. Session key encrypted with aes128 as usual Just like project 0 Signature of first two chunks signed with openssl sha1 | openssl rsautl -sign -inkey . ./john-keys/john-priv.pem Remember to remove newlines
Background image of page 4
Password Crackers: example word digest alabaster xf5yh@ae1 Hj68aan4%41 7%^^1j2labdGH albacore alkaline wont4get Pasword file /etc/passwd jones:72hadGKHHA% smith:HWjh234h*@!!j! jackl:UwuhWuhf12132^ taylor: Hj68aan4%41 knuth:ih*22882h*F@*8haa wirth:8w92h28fh*(Hh98H rivest:&shsdg&&hsgDGH2
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Making Things Harder: Salt In reality, Unix systems always add a two- character “salt” before hashing your password There are 4096 possible salts One is randomly chosen, appended to your password, then the whole thing is hashed Password file contains the digest and the salt (in the clear) This prevents attacking all passwords in /etc/passwd in parallel
Background image of page 6
Password Crackers: with Salt word digest alabaster xf5yh@ae1 7%^^1j2labdGH albacore alkaline wont4get Pasword file /etc/passwd jones:72hadGKHHA% H7 smith:HWjh234h*@!!j! YY jackl:UwuhWuhf12132^ a$ taylor: Hj68aan4%41 y$ Ja knuth:ih*22882h*F@*8haa U% wirth:8w92h28fh*(Hh98H *1 Table for Salt Value: A6 no match
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Fighting the Salt: 4096 Tables Crackers build 4096 tables, one for each salt value Build massive databases, on-line, for each salt 100’s of GB was a lot of storage a few years ago, but not any longer! Indexed for fast look-up Most any common password is found quickly by such a program Used by miscreants, but also by sysadmins to find weak passwords on their system
Background image of page 8
Getting the /etc/passwd File Public file, but only if you have an acct There have been tricks for remotely fetching the /etc/passwd file using ftp and other vulnerabilities Often this is all an attacker is after Very likely to find weak passwords and get on the machine Of course if you are a local user, no problem Removing the /etc/passwd from global view creates too many problems
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Shadowed Passwords One common approach is to put just the password digests into /etc/shadow /etc/passwd still has username, userid, groupid, home dir, shell, etc., but the digests are missing /etc/shadow has only the username and digests (and
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 55

CSCI6268L33 - Foundations of Network and Computer Security...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online