k. stoeckigt ([email protected]) password interception in a ssl/tls channel brice canvel...

K. Stoeckigt ([email protected])

Password interception in a Password interception in a SSL/TLS channelSSL/TLS channel

Brice CanvelLASEC Memo

02/2003http://lasecwww.epfl.ch/memo_ssl.shtml


Password interception in aPassword interception in aSSL/TLS channelSSL/TLS channel

Summary/OverviewSummary/Overview

Combine two attacks, a man-in-the-middle-attack and a side-attack and take the opportunity to get someone’s email password.



• Memo is not uniform about the assumption the reader already knows about security and/or networking, computer science → Information gap– “SSL stands for Secure Sockets Layer and TLS stands for

Transport Layer Security. These are methods for hiding the information two parties send to each other,…”

– “Then, when using a block cipher in CBC mode, the concatenated string MES|MAC is padded with padding PAD such that MES|MAC|PAD|LEN is of…”

Critical CommentsCritical Comments



• The connection between the explanation of the Timing-Attack and the Dictionary and Brute Force method in comparison to the Attack in practice is not obvious– Neither timing data nor Dictionary and Brute Force method is

mentioned in the “final” explanation

• Attack is possible, but very complex– Man-in-the-middle attack; hacker must be able to intercept the

connection between Client and Server → this is not easy

Critical Comments (II)Critical Comments (II)



• No further explanation to the graph

(What is 0 – 800 ? What kind of diagram is it ?)

Critical Comments (III)Critical Comments (III)



Client, running MS Outlook Express 6.x

IMAP Mail Server

Hacker

The Attack in Practice The Attack in Practice • User checks email using a secure

connection (Outlook checks mail every 5 minutes → Hacker has a free sessions every 5 minutes)

• Hacker intercepts the connection (connection is redirected (DNS spoofing), man-in-the-middle-attack)

• Email client sends login/password to server

XXXX LOGIN “username” “password” <13><10><MAC><PAD><LEN>

• Hacker tries to decrypt authentication method using a multisession version of CBC-PAD (side-attack)



• It is just a Memo → many information are missing

• Attack is possible, but it costs a huge amount of effort to attack the system

• “Full report available soon” → not until June• Counteractive measures have been released

(for OpenSSL)

ConclusionConclusion


Password interception in aPassword interception in aSSL/TLS channel ?SSL/TLS channel ?

• What else do you need to know to determine if your system is vulnerable ?

• Do you think this vulnerability is also a MS-Problem ?

QuestionQuestion

k. stoeckigt ([email protected]) password interception in a ssl/tls channel brice canvel...

Documents