USB BASED SECURE E-MAIL

David C. Wyld (Eds) : ICCSEA, SPPR, CSIA, WimoA - 2013
pp. 183–192, 2013. © CS & IT-CSCP 2013 DOI : 10.5121/csit.2013.3519
USB BASED SECURE E-MAIL
Rakesh Shukla1
, Garima Kuchhal2
, R.Phani Bhushan3
,
S. Venkataraman4
, Geeta Varadan5
ADRIN, Department of Space, Govt of India, Secunderabad, Andhra Pradesh
1
rakesh@adrin.res.in 2
garima.kuchhal@adrin.res.in
3
phani@adrin.res.in 4
kalka@adrin.res.in 5
geeta@adrin.res.in
ABSTRACT
E-mail Security[1] has been a growing concern over the past few years. The average individual,
who uses e-mail, naively believes that their e-mail is private and secure. The electronic world is
filled with snoopers who can access all types of data over the network. As the world goes
digital, with more and rawer information about individuals available electronically, the need
for security increases. Ubiquity and speed of email have made it increasingly effective. So
providing reliance over this medium has become an inevitable requirement. There are other
systems that provide specific security and are strongly tied to the mail servers and browsers [4].
To overcome this problem we propose HID Device based Secure E-mail which is immune to
root kits, botnets, man in the middle attack, phishing.
KEYWORDS
Encryption, Decryption, POP3, SMTP, Symmetric key, block cipher, key, variable key, USB,
XML Encryption
1. INTRODUCTION
USB Based E-mail Security Software deals in providing email security using SSL along with
security plug-in with symmetric key encryption and PKI Based Asymmetric key encryption
(public key and private key stored in the USB) between client and web server, and secure variable
key block cipher with base-64 encoding, between web server and email server. SSL certificates
are self signed generated using OpenSSL with SSL protocol (port 8443).
The USB based Secure E-mail Access System consists of an USB device which is ergonomically
designed hardware based on the USB interface [13]. The device has a finger print scanner
(biometric) for user authentication. The device has flash memory to store the reference fingerprint
database. It prevents the misuse of the user fingerprint database and also any mechanical opening
of the device. It turns its self destruction mode ON after three wrong authentication attempts (here
finger print scan). It destroys the fingerprint information; device memory etc. on the device by
writing unwanted information or garbage over the memory area. Every device has its own 16 digit
Unique ID (UID). After customization the device is set to read-only mode so that nothing can be
written on it. The crucial part of complete
System is that after booting the system through USB, it disintegrates the hard disk of the host
system. This makes the web browsing totally secure without leaving the traces of the work done
on the host system.

184 Computer Science & Information Technology (CS & IT)
Without the USB device [14], the Secure Speaking E-mail Software cannot be accessed. The
mandatory biometric authentication is made available through USB only. Cryptography key pairs
also reside in the USB device without which the software will not function.
2. GOAL
To provide E-mail Security [7,8] application through USB device. The basic features like
Confidentiality, Integrity, Authentication, Non-Repudiation and Availability have to be taken
under the security head.
3. SOFTWARE COMPONENTS
The secure email security solution uses POP3 [5,6] for retrieving the emails and SMTP [3] for
sending the emails. The Software works in a 3 tier architecture mode:
1. Web browser as client (HID Device)
2. Web Server as middle tier
3. E-mail Server as third tier
4. SOFTWARE FEATURES
4.1. Single Hop Email
The emails, which are sent under this category, can only be read. Such emails cannot be
forwarded further and gets deleted after a certain span of time. Such mails cannot be saved. The
contents cannot be copied. Copy and paste and other such keys are disabled in case of single hop
emails. Even the print screen facility is also disabled for such emails. We tried to get the print
screen figure of this facility to show how it works but could not as the print screen facility was
not working in this case.
Fig. 1. Flow diagram

Computer Science & Information Technology (CS & IT) 185
4.2. Speech Mode
The Emails, which are marked as speaking mails, will be read aloud when opened at the client
side. This facility can be used for persons who are blind. The output speech of such emails can be
taken onto a headset (a Bluetooth or a normal headset). The emails which are read are not visible
and only the voice can be heard. Two accents for voiceare available, namely British and
American English. These accents can be selected before the start of the software. The security is
fully taken care in this mode. In speech mode the security is taken care with the speech content
being decrypted at client side.
Permission can be set to make the contents viewable in case of speaking emails.
4.3. Spam filter
It takes care of the Spam and unsolicited mails. The facility of content filtering is incorporated to
remove any unwanted contents like attachments with extension exe, com, pif etc. Contents with
attachments like exe/zip/com/pif etc. can be stripped right before entering the user inbox.
4.4. Attachments
For sending the attachments there is no limit on the size and the number of attachments. But the
same can be set, by the administrator based on the policy of the organization/clients.
4.5. Vacation Mail
The facility of vacation message is provided for taking care of the client’s emails when he/she is
on leave. If a particular client is on vacation then he can set default reply to all mails and same
reply will be sent to all mails received.
4.6. Acknowledgement
To confirm the receipt of the e-mail, sender is prompted with an option of acknowledging the sent
mails.
Fig. 2. Single Hop Email

4.7. Auditing/logging
It is done at the administrator level by recording each and every minutest detail of the operations
done by each client. Such log files can be mined for retrieving important information.
5. SECURITY ASPECT
Strong user authentication is the paramount requirement for web computing that restrict illegal
access of web server. The proposed Secure Web server Application framework provides identity
management, multi factor client authentication, user privacy, session key establishment between
the users and the web server through Authentication Server. Since a web server is generally
vulnerable to several hacking attacks which means, it is more efficient to split the authentication
process of the client between the web server and an Authentication Server.
Fig. 3. Sequence/Data Flow diagram

The security of the software is taken care with SSL and security plug-in between the client and
the web server. SSL, Secure Socket Layer protocol works on the default port of 443 and provides
end to end security between any client and web server. It uses 128 bit key for internal encryption.
The protocol works on the transport layer and hence is application independent. SSL takes care of
the basic security considerations of integrity, privacy, confidentiality and non-repudiation. Apart
from this security plug-in form the second layer of security. The security plug-in form the end to
end security using an indigenous symmetric key block cipher algorithm. Third and last layer
consists of the security in the form of symmetric block cipher (with key size 448 bits) in a CBC
mode with changed IV (initialization vector) with Base-64 encoding. Present framework
strengthens security without compromising usability and ubiquity. The solution approaches
classical forms of shared-secret as username, password, hashing with see. It also implements
multifactor authentication.
Multifactor authentication refers to a compound implementation of two or more classes of
human-authentication factors:
• Something known to only the user—Knowledge-based (password).
• Something held by only the user—Possession-based (USB Dongle)
.
• Something inherent to only the user—Biological or behavior biometric traits (fingerprint).
Apart from SSL an additional layer of security is incorporated in the application. All the mails
communicated/transferred are encrypted at the web browser level (in USB [14]) and further
decrypted in the web browser only. This step strengthens the security independent of the web
server. Here whatever mail is transferred on the network channel is itself encrypted apart from
SSL. Security is ensured between each mail communication (mail sender and mail receiver). A
Symmetric key is generated at each transaction between server and client. The data is encrypted
with the symmetric key and cipher text is transmitted. The symmetric key is encrypted by
RSA key to enhance the security measures. Asymmetric Key pairs are hard coded on the
USB device at the time of its customization.

Mail from Client is
Decrypted (Secure
USB)
Cipher Text
(Encrypted with
Symm. Key)
XML Document (Encrypted data &
encrypted key)
Decrypt sym. key
with RSA Key
E-mail Server
(POP3/IMAP3)
Web Server
SECURESOCKETLAYERSECURESOCKETLAYER
Email from Client
(Secure USB)
Cipher Text
(Encrypted with
Symm. Key)
XML Document (Encrypted data &
encrypted key)
Web SERVER
Encrypt with RSA
Key
Symmetric Key
Generation
E-mail SERVER
(SMTP)
Fig. 4. Encryption of the mail at the client and send to the
web server along with decryption of the mail received.

5.1. XML Signatures
XML is used for communication between client and server. Since the whole communication is
secure, the need is of trustable and secure XML messages for transactions. One key to enables
USB BASED SECURITY
PLUGINS
Fig. 5. Security Aspects
<mail>
<encdata>
3A:A4:EF:23:E9:C7:AD:93:4D:9F:5A:C4:E7:B3:AF:C0:2
B:92:B3:0D:9D:D3:38:8E:30:D0:67:06:A7:F3:96:32:32:31:FE:66:F1:
A8:40:64:C6:4D:56:B4:D7:F5:1F:20:77:C9:AC:7E:69:76:39:E4:15:1B
:D1:6C:0A:12:F0:92:D6:00:E7:98:34:B0:2E:13:0D:06:FF:80:2C:9F:C
7:F1
</encdata>
<keydata>
51:47:7B:AA:C2:6E:E1:79:19:60:2F:12:3E:4F:63:43:55:9E
:AD:4A:EE:97:39:64:2D:F3:20:1A:CD:60:B4:FE:FB:FA:18:54:E9:2B
:E4:D3:6F:B9:94:1E:99:F0:AF:F0:A3:10:73:81:E7:49:75:0A:21:F9:E
E:3A:BB:65:06:13:A2:6E:BD:85:E5:EB:48:0F:49:D1:3F:D7:CE:1F:5
F:DF:2F:55:72:37:C2:99:4A:BE:F6:29:DC:86:ED:B7:FB:BD:27:71:6
7:50:22:69:47:80:08:9D:4C:98:65:0D:47:91:F7:15:E9:8A:A5:EC:97:1
0:28:A7:71:1B:75:B6:5D:33
</keydata>
</mail>
Fig. 6 Cipher Text through XML Encryption

secure transactions is the concept of a digital signature, ensuring the integrity and authenticity of
origin for documents. XML signatures are digital signatures which add authentication, data
integrity, and support for non-repudiation to the data that they sign. They address the special
issues and requirements that XML presents for signing operations and uses.
XML syntax for capturing the result, simplifying its integration into XML applications. XML
Encryption provides end-to-end security and is the natural way to handle complex requirements
for security in data interchange applications. It addresses following areas: - Encrypting part of the
data being exchanged and securing the sessions. Figure 6 shows a typical Cipher Text through
XML encryption.
6. SECURITY ANALYSIS
6.1. User privacy
The framework never transmits emails in plaintext form[8]. All the messages are transmitted over
the public channel in encrypted form.
6.2. Multi Factor Authentication:
User requires both simple credentials (user id and password) and hardware tokens (USB Device)
in order to gain access. The combination of the "known", "held" and "biometric factors" [9]
makes up the multifactor authentication method, and significantly improves the authentication
strength, as it curtails the threat of stolen digital identities.
6.3. Transaction key management:
A session is established between the user and the server after authentication process. The
transaction key is different in every client-server communication throughout the session.
6.4. Man in the middle attack:
The client private keys are not known to anybody else as they are present in the USB device only.
Similarly ID and PW are with the client only. Three wrong finger print scan will destroy the
device (Tamper proof).
6.5. Impersonation attack:
The framework never transmits user ID and PW directly through the public channel. Instead, ID
and PW are transmitted in encrypted form. The hash value of unique id of the Secure USB
Dongle is transmitted through out the communication (encrypted form). Also the framework
stores the h(PW) and h(UID) at the server. And also the Secure USB device has tamper protection
through biometric authentication (finger print scan).
6.6.Password guessing attack:
The framework allows user to have only strong passwords. Weak passwords or easily guessable
passwords are not allowed. Passwords should be minimum of 12 characters, must have at least
one number, one special character, no blank space and first character should not be an alphabet.
Moreover three wrong password attempts will block the Secure USB device for next 24hrs.

6.7. Insider attack:
Insider attack is the most hazardous threat to any inter-networking system. In the application the
password is never used openly, instead, it is digest h(PW). Moreover, attackers need the user
private key, and the USB Device [15] to get access to the web server. Only a genuine user can
provide private key, password and secure USB device (with biometric authentication)
simultaneously.
6.8. Fiestel Cipher:
The block cipher uses the operations, which are performed on both the halves of the data (i.e. 32
bits each) in each round. This enhances the cryptographic strength (additional operation is linear
XOR).
6.9. Brute Force Attack:
It is quite invulnerable as the key length can go up to 448 bits [2]. To add to this the sub key
process is very length with 521 executions required for a single key test.
6.10. Cryptanalysis:
Some tests have been done to cryptanalyse the algorithm but till now no practical weaknesses
have been found [10].
7. CONCLUSIONS
The application was developed with objective of providing E-mail security [11] in a restricted
secure environment. The application uses POP3, SMTP and has been tested to work for IMAP3
[6], POP3S, SMTPS and IMAP3S. The Standard HID provides Limited network accessibility
without any need of antivirus. On the top of it no trace of user actions either on host system or the
USB device are left. This further strengthens the security and maintains the privacy of the
user/client. Last but not the least ultimate goal is carrying the Secure E-mail access device along
with.
REFERENCES
[1] How to: Perform Actions When an E-Mail Message Is Received [http://msdn.microsoft.com/en-
us/library/ms268998(VS.80).aspx ].
[2] Bruce Schneier, “Applied Cryptography—Second Edition,” pg. 8.
[3] Postel, J.,"Simple Mail Transfer Protocol", STD 10, RFC 821, USC/Information Sciences Institute,
August 1982. [http://www.faqs.org/rfcs/rfc821.html]
[4] Crocker, D., "Standard for the Format of ARPA-Internet Text Messages", STD 11, RFC 822,
University of Delaware, August 1982. [http://www.faqs.org/rfcs/rfc822.html]
[5] Dover Beach Consulting, Inc. "Post Office Protocol - Version 3", RFC 1725, Carnegie Mellon,
November 1994. [http://www.faqs.org/rfcs/rfc1725.html]
[6] M. Crispin, University of Washington "Internet Message Access Protocol – Version 4", RFC 1730,
December 1994. [http://www.faqs.org/rfcs/rfc1730.html]
[7] Douglas R. Stinson,”Cryptography Theory and Practice”.
[8] Bruce Schneier, David Banisar,“ The Electronic Privacy Papers: Documents on the Battle for
Privacy”.
[9] Bruce Schneier,“ E-mail Security: How to Keep Your Electronic Messages Private”.
[10] Bruce Schneier,“ E-mail Security”.

[11] Bradley F Shimmin,“Effective E-mail Clearly Explained: File Transfer, Security, and
Interoperability”.
[12] [http://news.cnet.com/IBM-brains-capture-a-PCs-soul/2100-1041_3-5830870.html]
[13] Boot from a USB Drive Even if your BIOS Won’t Let You (How-To Geek)
[14] [http://www.pendrivelinux.com/2007/11/21/use-a-floppy-to-boot-usb-pendrive-linux/ boot floppy for
live USB]
[15] [http://www.pendrivelinux.com/usb-minime-2008-install-from-windows]
Authors
Rakesh Shukla is working in the Systems Engineering Group, ADRIN, Dept. of Space, as
Sci./Engg. “SE” and involved in developing applications on network and data security.
He can be contacted at rakesh@adrin.res.in
Garima Kuchhal is presently working in Systems Engineering Group, ADRIN,
Department of Space, as Sci/Engr. ‘SC’ and involved in development of secure web
based applications. She can be contacted at garimakuchhal07@gmail.com
Mr. R.Phani Bhushan is working as Section Head, Data Security Section under the
Systems Engineering Group, ADRIN, Dept. of Space. He is involved in developing
applications on Mobile Ph ones based on GSM/GPRS technology besides leading a group
involved in development activities in both host based and network based security. He can
be contacted at phani@ adrin.res.in
Dr. S. Venkataraman, is the Group Director and heading the Systems Engineering
Group. He can be contacted at kalka@ adrin.res.in
Mrs. Geeta Varadan is Director, ADRIN, Dept. of Space. She can be contacted at geeta@
adrin.res.in

USB BASED SECURE E-MAIL

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USB BASED SECURE E-MAIL