- Two early secure email systems were PEM (Private Enhanced Mail) and PGP (Pretty Good Privacy). PGP became the de facto standard. - PGP uses algorithms like IDEA for encryption, RSA for key exchange and signatures, and MD5 for hashing. Version 2.6.3i from the 1990s is often used to explain basic PGP operations. - PGP can encrypt files locally using a passphrase to derive an IDEA encryption key via MD5 hashing. It can also encrypt emails using a randomly generated IDEA session key which is encrypted with the recipient's RSA public key.

1. Secure Mail Applications
Presented by:-
Ashok Panwar
Technical Officer in ECIL (NPCIL)
Tarapur, Mumbai
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2. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 2
From both, PGP has been the one that became an standard for
secure e-mail clients on closed environments.
Therefore we'll see only some of the generic aspects of PEM and we
will analyze PGP in deeply.
The secure e-mail
In the beginning of the 90´s two systems or applications of secure
email appear:
 PEM: Private Enhanced Mail
 PGP: Pretty Good Privacy
On open systems as in the case of the Internet, the secure email is
achieved through the plataform S/MIME which means Secure
Multipurpose Internet Mail Extensions.

3. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 3
• It is a proposal of the IETF Internet Engineering Task Force in
1985. The technic document is published in 1993.
• The technic specifications are in RFCs Request For Comments
numbers 1421, 1422, 1423 and 1424.
• It used to link to protocol SMTP Simple Mail Internet Protocol.
• Encryption of the information: DES in CBC mode.
• Generation and key management: RSA from 508 to 1024 bits.
Structure of certificates as per the X.509 rule.
• Session key: DES in CBC mode, Triple DES-EDE.
• Digital signature: RSA, MD2, MD5.
Private Enhanced Mail PEM

4. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 4
 It is compatible with other engineering models like, for
example, X.400.
 PEM is implemented at the application level:
It is independent from the protocols of the OSI levels
or from lower TCP/IP levels.
It is independent from the operating systems or from
the computer.
 It can be implemented as an independent module that
works with the common email client for the user.
PEM Implementation

5. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 5
 Security services contemplated:
Source authentication.
Confidentiality.
Integrity of the message.
Non repudiation of the source when key management
with asymmetric key algorithm is used.
 Security services not contemplated:
Access control.
Confidentiality in the traffic of the messages.
Non repudiation of the message by the receiver.
Security services in PEM

6. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 6
 TIS/PEM
UNIX Plataforms UNIX. Trusted
Information System. Source code
available for citizens or companies from
USA or Canada. It uses a hierarchy of
multilple certification.
 RIPEM
It implements part of the PEM protocols
without certificates for keys
authentication. Free for non commercial
applications. Export forbidden out of the
United States. There are versions
utilized all over the world.
Format and implementation of PEM
Header of the E-mail Service
(Headers of RFC822)
Encapsuled header
Fields related to authentication,
integrity and confidentiality
Encapsuled text
User's message with some optional
fields
Blank line

7. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 7
 Philip Zimmermann publishes the version 1.0 of PGP in 1991
with minimum requirements of hardware and software.
 In 1992 appears version 2.0 on which programmers from all
over the world participate. Its code it's written out of USA to
avoid the restrictive laws regarding cryptography software and
its legal problems.
 In 1993 version 2.3a appears that is very popular on FTP sites
and valid for several platforms of operating systems.
 In 1994 the Massachusetts Institute of Technology MIT
participates on the project and versions 2.4, 2.5 and 2.6 appear.
 Version 2.6.3i is popularized globally.
Pretty Good Privacy (PGP)

8. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 8
Though there is more than a software offer for secure mail
besides the PGP program, this became an standard in fact.
Although the last versions of the program oriented to
Windows environments present high capability, the basic
operations continue being the same as in knowing version
2.6.3i.
The new PGP versions on the Windows environment change
very fast therefore it is very difficult to have up-to-date
notes permanently. That's why the version 2.6.3i will be
used as a simple version for explanation of the cipher and
signing operations with PGP and, subsequently, we'll go
through the characteristics of versions 6.5.1 and 8.0, one of
the lasts.
Explanatory note about PGP versions
The philosophy of new versions is exactly the same...

9. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 9
 If you don´t know PGP or you have never worked with this
environment, I recommend you to download from the Web
page of the Thematic Netowork CriptoRed the file of PGP
2.6.3i Guide on html format indicated. (SW in Spanish).
 This application will be useful to lern quickly the
commands and utilities of this PGP version, very similar to
the current ones. PGP 2.6.3i has a size less than a 1,4 MB
diskette, though all its operations are in command mode.
PGP Guide 2.6.3i



10. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 10
 PGP, on version 2.6.3i (international) became in the
middle of 90´s on a standard. In fact, many users “are still
faithful” to this version.
 It encrypts all different type of data on MS-DOS and
UNIX environments. Its main orientation is the encryption
of the data and the digital signature on electronic mail.
 The basic algorithms that it uses are:
 IDEA to encrypt with secret key system.
 RSA for key agreement and digital signature.
 MD5 for obtaining the hash function of the digital
signature to recover asymmetric private keys and local
encryption.
Characteristics of PGP 2.6.3i

11. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 11
Compression ZIP • The plaintext and the signature are compressed in order
to be stored or transmitted.
Generation of Keys RSA, MD5 • It generates a public and a private key, finding two prime
numbers very high. The private value is kept encrypted
with IDEA using as the key an MD5 hash of the secret
pass sentence.
Conventional Cipher IDEA • It encrypts the message with a random session key of
128 bits (unique) generated on the sender randomly.
Key Agreement IDEA, RSA • It encrypts the IDEA session key with the public key of
the receiver with RSA and add it to the cryptogram.
Digital Signature MD5, RSA • Hash function MD5 generates a hash of 128 bits, that
represents the complete plaintext, and that is encrypted
with RSA with the private key of the sender. It is added to
the sent message.
E-mail Compatibility Base-64 • It permits to transmit the message to every type of e-mail
applications. It converts the octets into printable
characters.
Segmentation • It divides the final cryptogram into blocks less than
50.000 bytes so that they are transmitted correctly on the
Internet and also recovered right.
Algorithms used in PGP 2.6.3i

12. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 12
 This operation is useful to maintain protected
files, for instance on the hard drive.
 The access to the plaintext will only be possible if
a key or passphrase that is the passphrase used for
encrypting is known.
 Remember that if after encrypting the file you
physically delete the plaintext -operation that
makes a recording of random ones and zeros on
the storage zone of the disk. it will be impossible
to recover it if you forget the passphrase or secret
key.
Characteristics of local encryption

13. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 13
Steps:
1. PGP requests a passphrase: this must be long
enough to avoid combination attacks.
2. The hash algorithm MD5 is applied to that
passphrase, generating so a 128 bits key.
3. With that key, PGP encrypts the document with
algorithm IDEA and makes its extension .pgp.
4. As an option, it permits then to make a physical
erase of the plainfile.
Steps of local encryption with IDEA

14. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 14
Plain Text
PASSWORD
Local Key
with 128 bits
Encrypted
Text
The password is a passphrase. It is
recommended that it has spaces, signs
and punctuation characters
The document is compressed with
ZIP algorithm
The encrypted file
can be saved, for
example, on the
disk.
Optional erase of
the plaintext
Every new cipher requires a password. This can be equal or different.
Remember that with equal password (passphrase), we'll have equal hash.
Scheme of local encryption with IDEA

15. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 15
 PGP operations to encrypt, decrypt, sign and the
subsequent checking of the digital signature, use the
algorithms of the hash functions, with public key and
secret key seen in previous chapters of this book.
 In order to send and receive secure mail, it is necessary to
count at least with the following keys:
Public key of the receiver.
Pair of asymmetric keys of sender.
Generation of keys with RSA
Operations with asymmetric keys

16. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 16
Steps:
1. PGP generates a random number of 128 bits that will be the
session key.
2. The message is encrypted with such key using IDEA.
3. The session key is encrypted with the RSA public key of the
receiver and is added to the cryptogram.
4. The identifier ID of the public key of the receiver is added to
the session key encrypted on step 3 as an indicative of the
receiver's identity.
Encryption steps with destination public key
Remember that the e-mail usually is not a real time communication so,
though a key is sent to decrypt the cryptogram on the receiver's side, it is not a
session key in the same terms on which it is used, for instance, on an SSL
communication.

17. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 17
Plain
Text
Destination's
public key
EncryptedTe
xt
Encryptedse
ssion key
Session
Key
It is seeked on the sender's
public key ring
The document is compressed
before with the ZIP algorithm
We need a session
key ...
Because of compatibility
on e-mail client systems,
an armour (Base 64) is
added before transmitting
it
Encryption with destination public key

18. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 18
Steps:
1. PGP seeks on the head of the cryptogram the
identifier ID of the user (receiver) that has been
added on the encrypted session key.
2. The private key of the identifier ID is searched on
the private key ring of the receiver.
3. The private key in plain is accessed, decrypting it
with IDEA when the owner ID introduces its
passphrase and the MD5 hash brings the decryption
key.
4. With the private key the session key is decrypted.
5. With the session key the cryptogram is decrypted.
Decryption steps with destination private key

19. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 19
It is searched on the private
key ring of the receiver
Encrypted
Text
Encrypted
session
key
receiver private
key encrypted
PASSWORD
Decrypted
private key
Session
key
Plain
TextThe armour is finally removed and it is decompressed
Decryption with destination private key

20. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 20
Plain
Text
Digital
signature
block
Plain
Text
IDEA Encrypt-
ed Private key
PASSWORD
Decrypted
private key
A plain text will be encrypted
We need our private
key...
It can be sent encrypted
if needed as well
Digital signature RSA

21. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 21
Public key of the
sender
Digital
signature block
PlainText
received
EQUALS ?
Correct
signature
Incorrect
signature
The sender public key is seeked to
decrypt signature
The hash function of the message is calculated on
destination and then we start comparing
Yes
No
RSA digital signature checking
h(M) sent
h(M)
calculated

22. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 22
NAME OF THE FILE
IDENTIFIER OF PUBLIC KEY OF RECEIVER
SESSION KEY
SEAL OF TIME
IDENTIFIER OF PUBLIC KEY OF SENDER
HASH OF THE MESSAGE
TEXT OF THE USER
COMPONENTS
OF SIGNATURE
COMPONENTS
OF MESSAGE
TWO FIRST OCTETS OF THE HASH
SEAL OF TIME
COMPONENTS OF
SESSION KEY
ZIP
E(eB)
R64
Order of operations
Format of a PGP message addressed to B

23. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 23
 Generation of keys
RSA: 1.024 - 4.096 bits
Diffie & Hellman: 1.024 - 4.096 bits
 Digital signature
DSS (Digital Signature Standard): 1.024 bits
 Encryption
AES, CAST, IDEA, TripleDES, Twofish
 Hash
SHA-1 (160 bits) and MD5 (128 bits)
Algorithms on new PGP versions

24. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 24
From version 5.0 to the current ones (versions 8.0 and next) the local
encryption schemes, asymmetric cipher and digital signature have changed
very little though they present bigger capabilities. Nevertheless, remember
that some capabilities will only be activated on commercial versions.
Some versions of PGP in Windows
PGP 6.5.1 PGP 7.0.3 PGP 8.0

25. Presented by:- Ashok Panwar
Technical Officer in ECIL
Page 25
Secure mail through S/MIME
 S/MIME: Secure Multipurpose Internet Mail Extensions
 Unlike the standard PGP, that is based on the trust among users,
S/MIME uses digital certificates X.509 brought by a Certification
Authority that the e-mail clients must recognized as such.
 It will add encryption and signature services on the e-mail clients
(Outlook Express, Netscape Messenger, ...) in MIME format.
 It creates such an envelope on which the data are embedded
encrypted and/or signed.
 It uses platforms of standards PKCS, Public-Key Cryptography
Standards.


26. Any Questions ???
Thanks !!!
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