understanding
email encryption
Nicolas T. Courtois
- University College London
email Encryption
Conventional Encryption
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Nicolas T. Courtois
email Encryption
Secret-Key Encryption
Bob
Alice
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Nicolas T. Courtois
email Encryption
Secret-Key Encryption
Bob
Alice
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Nicolas T. Courtois
email Encryption
Example
Truecrypt hard drive encryption
Danger: shared key…
If only one computer is infected…
all security gone forever (past, future, all people)
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Nicolas T. Courtois
email Encryption
Asymmetric Techniques
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Nicolas T. Courtois
email Encryption
Vocabulary
Public-Key Cryptography ==
Asymmetric Cryptography
there is no secret in encryption,
there is one in decryption
•
•
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A Private Key =a.k.a.= Secret Key
A Public Key.
Nicolas T. Courtois
email Encryption
Public Key Cryptography
Public key:
can be distributed to
many parties.
Does not have to be
public
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email Encryption
Public Key Encryption - 3 Algorithms
r
m
m or invalid
Eve
encryption
algorithm
c
c
decryption
algorithm
past: setup phase
pk
(public key)
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Nicolas T. Courtois
key generation
algorithm
sk
(private key)
email Encryption
Setup / Establishing Trust
(PKI=Public Key Infrastructure)
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Nicolas T. Courtois
email Encryption
SKA PKA
What’s Wrong Here?
PKA
EPK(A)(m)
B
A
Key management?
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Nicolas T. Courtois
email Encryption
SKA PKA
Even More Wrong
PKCert
PKA
EPK(A)(m)
B
A
a dog?
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Nicolas T. Courtois
email Encryption
SKA PKA
Right Solution with PKI
PKA
PKCert
certA
h(rB), B, EPK(A)(rB, B)
B
A
authentication of the key by the means of a Digital Signature
signatures suddenly needed ALSO FOR ENCRYPTION
PGP will ask us to sign keys… proof of trust
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email Encryption
Digital Signatures
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email Encryption
[Manual and Digital] Signatures
Two main functions:
1. Identify the signer
2. Approbation of the document.
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email Encryption
Manual  Digital Signatures
Two main functions
1. Identify the signer
2. Approbation
…in electronic word:
1. Easy to copy !
2. Easy to alter the
document !
Consequence => A digital signature
does depend on the document.
(need to protect document integrity,
did not exist before !)
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Nicolas T. Courtois
email Encryption
Digital Signatures
m
signing
algorithm
yes/no
(m,)

verification
algorithm
forgery
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sk
pk
(private key)
(public key)
Nicolas T. Courtois
email Encryption
Requirements so far:
Three main functions:
1. Identify the signer
2. Approbation
3. Integrity of the message
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email Encryption
Integrity: Hash-then-Sign
m
A hash function (or hash algorithm) is a
reproducible method of turning data
(usually a message or a file) into a
number suitable to be handled by a
computer. These functions provide a way
of creating a small digital "fingerprint"
from any kind of data. The function chops
and mixes (i.e., substitutes or transposes)
the data to create the fingerprint, often
called a hash value. The hash value is
commonly represented as a short string
of random-looking letters and numbers
(Binary data written in hexadecimal
notation).
0- bits
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Nicolas T. Courtois
H(m)
H
Digital
Signature
e.g. RSAPSS
>=160 bits

098f6bcd46
21d373cade
4e832627b4
>=80 bits
email Encryption
Digital Signatures - Bonus
Another main function !
1. Identify the signer (certify origin, solved)
2. Approbation (hard to get !)
3. Integrity of the message (solved)
4. Automatic verification,
and another bonus:
Public Verifiability
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Nicolas T. Courtois
email Encryption
Vocabulary
frequently confused
crypto only
•crypto - a D.S.
Digital Signatures
•secure device
•qualified certif.

Advanced Electronic Signatures.

Electronic Signatures.
just some electronic tag/evidence…
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Nicolas T. Courtois
email Encryption
Electronic and Advanced Signatures
(in The European Directive)
1. Electronic Signature.
Definition [EU]: data in electronic form which are attached to, or logically associated
with, other electronic data and which serve as a method of authentication.
2. Advanced Electronic Signature.
2x link.
An electronic signature that:
•
is uniquely linked to a signatory and capable of identifying the signatory,
and created by means the signatory can maintain under his sole control,
•
and linked to the data being signed such that any change of the data is
detectable.
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Nicolas T. Courtois
email Encryption
Non Repudiation
1. Identify the signer
Non-repudiation (aka Imputability).
The signer is the ONLY and UNIQUE person
which can create the (signed) document.
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email Encryption
Protocols and Software Products:
Security of Email
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email Encryption
SMTP Protocol
THE original email protocol.
Emails: no encryption (in cleartext) and no authentication.
In addition everybody can send email
=> epidemics of spam!!!!
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email Encryption
Standards for Secure Email
Two main open standards:
•
PGP
–
–
–
•
[Phil Zimmerman, US activist, 1991],
much later became open standard GnuPG [RFC2440]
some PGP products are certified by US gov NIST
S/MIME [RSA Labs]
–
free implementation in Open SSL
same general method called hybrid encryption:
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Nicolas T. Courtois
email Encryption
Hybrid Encryption
random
key K
IV mi
mi
Data Encapsulation Module
K
block
cipher +
mode
block
cipher +
mode
Eve
ci
K
ci
Key Encapsulation Module
r
PK encryption
algorithm +
K “good” padding
encapsulated
key
PK decryption
algorithm +
verif. padding
past: setup phase
pk
(public key)
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key generation
algorithm
sk
(private key)
K
email Encryption
Background
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email Encryption
Why Encrypt Email?
Phil Zimmerman writes:
Why don't you always send your paper mail on
postcards? […]
You must be a subversive or a drug dealer if you hide
your mail inside envelopes. […]
Are you trying to hide something?
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email Encryption
PGP Revolution
Zimmerman in 1991 wrote the first email encryption program
which was adopted worldwide. He says:
:
Intelligence agencies have access to good
cryptographic technology.
So do the big arms and drug traffickers
[…]
But ordinary people and grassroots political
organisations didn’t have…
[…]
Until now.
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email Encryption
How to use PGP
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email Encryption
Software 1+2
Frequently there are two separate programs:
1. Key management and command line tool
–
–
PGP=paid,
GnuPG = free
2. Encryption/Decryption/Signature/Verification
programs or front-ends
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email Encryption
Example
1. Install GnuPG from gnupg.org
2. Instal Enigmail -- for Mozilla Thunderbird
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email Encryption
Software
1. Key management and command line:
•
–
–
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Example: GnuPG from gnupg.orgGnuPG (free GNU
version of PGP = RFC4880)
Almost invisible tool, works in the background…
Download from gnupg.org
•
•
Requires a compiler such as Visual Studio 8, use nmake or so..
Version 1.4.9. Easy to install:
http://www.mirrorservice.org/sites/ftp.gnupg.org/gcrypt/binary/g
nupg-w32cli-1.4.9.exe
•
•
Version 2.0. is provided by third party:
http://gpg4win.de/download.html
Nicolas T. Courtois
email Encryption
Example – 1.
After installation:
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email Encryption
Software 2.
2. Encryption/Decryption/Signature/Verification
• Frontends: http://gnupg.org/related_software/frontends.en.html
•
•
•
•
•
•
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Enigmail -- for Mozilla Thunderbird
Enigform ---- Mozilla Firefox
EudoraGPG --- for Eudora
ez-pine-gpg ---- pine
GPGOE ---- plugin for Outlook Express
Mac GNU Privacy Guard , GPGMail etc.. ---- for Apple
Nicolas T. Courtois
email Encryption
3. Encrypt plain text?
Text<->text programs -- cut and paste (works with gmail
and IM!)
GPG4Win – on Windows
allows to encrypt files/email/text easily
Mc OS X:
• GPGDropThing –
• FireGPG which is a Firefox plugin. How to use it?
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Nicolas T. Courtois
email Encryption
PGP with Gmail and Mac 0S
•
Step 1. Right click, select FireGPG->Encrypt
Then and the end there is a
COPY TO CLIPBOARD AND CLOSE option
•
then paste the encrypted
message in Gmail.
creates also
a button
to encrypt
attachments
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Nicolas T. Courtois
email Encryption
Example - Enigmail
2. Instal Enigmail -- for Mozilla Thunderbird
From here:
https://addons.mozilla.org/enUS/thunderbird/downloads/file/92940/enigmail-1.1.2-tb-win.xpi
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Nicolas T. Courtois
email Encryption
Enigmail -- for Mozilla Thunderbird
MUST BE ADDED MANUALLY HERE,
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Nicolas T. Courtois
email Encryption
Enigmail -- for Mozilla Thunderbird
Add it manually!
Start Thunderbird. In the menu bar of the main window you will see "Tools". Select this, and
then "Add-ons". This will bring up a new window listing all of your Thunderbird plug-ins.
In the lower left-hand corner of this new window you'll see a button marked "Install".
Click this button. Tell Thunderbird where you saved the Enigmail .XPI file.
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Nicolas T. Courtois
email Encryption
Example
Enigmail -- for Mozilla Thunderbird
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Nicolas T. Courtois
email Encryption
My Keys
…
…
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Nicolas T. Courtois
email Encryption
Their Properties
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Nicolas T. Courtois
email Encryption
Right Click on One Key
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email Encryption
Key Properties
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Nicolas T. Courtois
email Encryption
Steps
1.
2.
3.
4.
5.
Install GnuPG software
Generate a pair of keys.
Choose a strong password for storage of…
Sign your own and other people’s keys. Why?
Make your key known (publish or distribute).
6.
Install an encryption/decryption program or a plug-in for
Eudora/Thunderbird/etc.
Now:
7.
–
–
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Everybody can write a PRIVATE encrypted message to you,
only you can..
You can sign any message,
everybody can check it comes from you,
nobody can…
Nicolas T. Courtois
email Encryption
Key Management
Sign your own and other people’s keys.
Why?
How?
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email Encryption
Problems with PK crypto
and email encryption
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Nicolas T. Courtois
email Encryption
Revolutionary or Dangerous?
The US Customs started a criminal investigation of
Zimmermann, for allegedly violating
the Arms Export Control Act…
Dropped after 3 years of investigation
and a lot of public/press outrage…
Named one of the:
•
Top 10 Innovators in E-business (InfoWorld)
•
50 most influential people on the Internet (Newsweek)
•
Etc.
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Nicolas T. Courtois
email Encryption
•
•
* Problems with the PKI Systems
Cf. Ellison and Schneier: “Ten Risks of PKI: What You're Not Being
Told About Public Key Infrastructure”
http://www.schneier.com/paper-pki.pdf
Ben Laurie: Seven and a Half Non-risks of PKI.
http://www.apache-ssl.org/7.5things.txt
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Nicolas T. Courtois
email Encryption
Main Risks / Pitfalls
1.
2.
Bugs? Backdoors? Source code? People/country trusted?
Is it really the key of Bob?
•
3.
Was his real key lost or stolen (e.g. virus)?
•
4.
5.
size (1024 bit: expired 2010)
strength (RSA-PSS 2048 bits)
randomness (mouse keyboard…)
Was the message changed at signing time?
•
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Revocation Lists: lists of blacklisted keys stored on an Internet
server
Was my key of good quality?
•
•
•
6.
7.
Certificates: trusting third parties in foreign countries
Real-time substitution
Did parties perform all the checks?
Shall I save the message?
Nicolas T. Courtois
email Encryption
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Nicolas T. Courtois
**Attack Tree
for PGP
© Bruce
Schneier
email Encryption
PKI Comparison
•
PGP
–
web of trust, totally decentralized system
•
•
•
•
users can chose how much they trust each key
is trust transitive? not really
in particular, can also implement normal hierarchical PKI.
S/MIME [RSA Labs]
–
uses the same standard PKI as SSL: X.509 certificates.
In both cases organisations can implement their own closed PKI.
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Nicolas T. Courtois
email Encryption
Happy with Secure Email?
Problems:
BUT:
• almost never used,
–
•
if signatures were the default behaviour, we would
maybe have less spam?
need to enrol in advance before email is sent…
–
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very few people have keys,
Nicolas T. Courtois
email Encryption
Email Storage
Questions:
•
should received and decrypted email be stored
encrypted?
•
why when sending a message we sometimes need to add
ourselves to the recipient list?
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Nicolas T. Courtois
email Encryption
Happy with Secure Email?
Problems kind of solved:
•
confidentiality
•
authenticity
Unsolved problems:
•
privacy of the recipient
•
privacy of the sender
•
hiding the existence of the message (=> Steganography).
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