Description
1 Project description
The objective of this project is to implement the various components of a security-enhanced EMAIL system
similar to PGP (Pretty Good Privacy) and GnuPG which is based on the OpenPGP standard. The cryptographic libraries from the OpenSSL (http://www.openssl.org) will be used.
1.1 Encrypted Email
The task is: Given an email message from User A to User B, message digest algorithm, encryption algorithm and the public/private key pairs of users, generate a security-enhanced output message that will
handle: (a) Confidentiality ONLY, (b) Authentication/Integrity ONLY and (c) Authentication/Integrity and
Confidentiality.
We will assume that for a given set of users, the corresponding public/private key pair is locally available.
In reality, the public key information for each user is available from some keyserver and the private key is
held securely by each user.
For this project, we will assume that Triple-key 3DES, AES, and Blowfish are available. We will assume
that only ECB mode is used – hence no need for Initialization Vector, Counter, etc.
The encryption steps are explained in detail in Stallings’ textbook. In order to achieve the different levels of
security/privacy, the following mechanisms are used:
Confidentiality ONLY (CONF):
Sender: The email message is encrypted with a randomly generated secret message key (or session
key) using a symmetric block cipher algorithm. The message key is encrypted using the receiver’s
public key and pre-pended to the message. The [encrypted key, message] is then written into a file
that can be sent using traditional email.
In essence, given input text M from user A to user B, the transmitted message C is:
C =
h
EKUb
(Ks, IVs) k E
des3
Ks
(M)
i
where Ks is the session key (and any needed initialization vector, IVs) and EKUb
is receiver’s public
key.
Receiver: The receiver uses its private key to decrypt the secret message key from the message file.
This secret key is then fed to the decryption algorithm on the remainder of the message file to extract
the plain-text message.
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Authentication/Integrity ONLY (AUIN):
Sender: A message digest or hash of the given plain-text message is generated. The digest/hash is
then encrypted using the sender’s private key. The [encrypted hash, message] is then written into a
file that can be sent using traditional email.
In essence, given input text M from user A to user B, the transmitted message C is:
C =
h
EKRa
Hsha1
(M)
k M
i
where EKRa
is sender’s private key.
Receiver: The receiver reads the encrypted hash from the message file and decrypts using the sender’s
public key to generate the hash. The digest/hash of the remainder of the message file is computed and
compared to the decrypted hash. If they match, success is declared.
Confidentiality and Authentication/Integrity (COAI):
Sender: A message digest or hash of the given plain-text message is generated. The digest/hash is
then encrypted using the sender’s private key. The [encrypted hash, message] is then encrypted with
a randomly generated secret message key (or session key) using a symmetric block cipher algorithm.
The message key is encrypted using the receiver’s public key and pre-pended to the message. The
[encrypted key, encrypted hash, message] is then written into a file that can be sent using traditional
email.
In essence, given input text M from user A to user B, the transmitted message C is:
C =
h
EKUb
(Ks, IVs) k E
des3
Ks
EKRa
Hsha1
(M)
k M
i
where Ks is the session key (and any needed initialization vector, IVs), EKRa
is sender’s private key
and EKUb
is receiver’s public key.
Receiver: The receiver performs the reverse operation to verify the sender, integrity and to extract the
plain-text message.
1.2 User Interface
The following are the necessary commands:
. ./proj2 CreateKeys UserNameListFile
The UserNameListFile will contain a set of users, one per line. For each user, randomly generate an
RSA key pair and store private key and public key in user priv.txt and user pub.txt respectively.
. ./proj2 CreateMail SecType Sender Receiver EmailInputFile EmailOutputFile DigestAlg EncryAlg
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SecType: CONF, AUIN, COAI are three possible string values for the three cases listed earlier.
Sender/Receiver are sender and recipient of this message.
EmailInputFile contains the input plain-text file (in ASCII format)
EmailOutputFile contains the output of the encryption algorithms (in binary format)
DigestAlg: One of: sha1, sha256
EncryAlg: bf-ecb, des3, aes-128-ecb
. ./proj2 ReadMail SecType Sender Receiver SecureInputFile PlainTextOutputFile DigestAlg EncryAlg
Similar to above.
1.3 Output File Format:
CONF: Line 1: Encrypted Secret Key
Line 2 onwards: Encrypted Data
AUIN: Line 1: Encrypted Hash/Digest
Line 2 onwards: Plaintext Data
COAI: Line 1: Encrypted Secret Key
Line 2: Encrypted [Hash/Digest+MessageData]
2 Starting Point
2.1 System Calls
At the least, the following system calls will be required . On Linux, man command or info command will
provide you with relevant information. You can run ’man evp’, ’man rsa’, ’man pem’ for lots of additional
information. You should know or learn how to read function interface descriptions from man pages and use
them correctly.
Note: By default, the crypto functions produce binary output. You must choose base64 encoded output
format.
3 Sample Session
Assume that you have created the files lab2.c and the corresponding executables in your LAB2 directory.
% cd LAB2
% make proj2
…
% pico Usernames.txt
… file will contain a set of 10-15 users
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% ./proj2 CreateKeys Usernames.txt
% ls -l *_priv.txt *_pub.txt
% pico Mail-sample.txt
… file will contain input text message.
% ./proj2 CreateMail COAI alice bob Mail-sample.txt Mail-out.txt sha1 bf-ecb
.. Encrypted File is created.
% ./proj2 CreateMail COAI alice bob Mail-out.txt Mail-decrypt.txt sha1 bf-ecb
.. Decryption operation
% diff Mail-sample.txt Mail-decrypt.txt
.. Any differences?
4 What to Submit
Name your project directory as LAB2 (Note: ALL UPPERCASE)
Once you are ready to submit, change directory to the directory above LAB2, and tar all files in the directory
with the command:
tar czf Lab2-RollNo.tgz LAB2
Then, submit it online on Moodle.
The directory should contain the following files:
. Source Files
. Makefile
Typing command ‘make’ at the UNIX command prompt, should generate all the required executables.
. A Script file obtained by running UNIX command script which will record the way you have finally
tested your program.
. a README file containing instructions to compile, run and test your program. The README should
document known error cases and weaknesses with the program.
. a COMMENTS file which describes your experience with the project, suggestions for change, and
anything else you may wish to say regarding this project. This is your opportunity for feedback, and
will be very helpful.
5 Help
1. WARNING ABOUT ACADEMIC DISHONESTY: Do not share or discuss your work with anyone
else. The work YOU submit SHOULD be the result of YOUR efforts. Any violation of this policy
will result in an automatic ZERO on the project, a potential F in the course, and other academic action.
2. Ask questions EARLY. Do not wait until the week before. This project is quite time-consuming.
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3. Implement the solutions, step by step. Trying to write the entire program in one shot, and compiling
the program will lead to frustration, more than anything else.
For example, implement the message digest first, then try encryption with secret key, then try encryption with public/private key, etc.
4. You can always verify the intermediate outputs using the openssl command line interface that was
demonstrated in class.
6 Grading
. CONF: 30 points
. AUIN: 30 points
. COAI: 40 points
No README/COMMENTS: -5 points; No Script File: -10 points; Incomplete Compilation: -10 points
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