Schmidt-Samoa Cryptography

Short Description

This is a program that can fully encrypt and decrypt messages according to a public/private key pair. There are three executable components:

1. A key pair can be generated using the keygen program
2. A message can be encrypted using the encrypt program and the generated public key file
3. An encrypted message can be decrypted to the original message using the decrypt program and the previously generated private key file

GNU Multi-Precision Library

To safely encrypt messages, the sizes of the integers used exceeds 64 bits of precision, the maximum for default C types. As a result, the GNU Multi-Precision Library (GMP for short) is utilized. Due to added complexity, comments describing operations in plain C are often incorporated next to the used GMP functions. The library for GMP can be found here: GMP Library

How to Build

To build, you must have the Makefile. This operates by collecting the C files, generating the object files, and linking them into the binary executable. You must have all of the .c and .h files from this repository to build. Once you have all the appropriate files, you can build each executable independantly or all together at once. To build all the files:

make

or

make all

To make each executable independantly:

make keygen
make encrypt
make decrypt

To see the command line arguments for each executable, run the following commands or see below.

./keygen -h
./encrypt -h
./decrypt -h 

Keygen Command Line Arguments

• -b bits: Makes public key greater than or equal to bits number of bits (Default: 256 bits)
• -i iters: Specifies iters number of iterations for Miller-Rabin primality test (Default: 50 iterations)
• -n pbfile: Specifies pbfile to store public key (Default: ss.pub)
• -d pvfile: Specifies pvfile to store private keys (Default: ss.priv)
• -s seed: Specifies seed for random state initializations, used for testing purposes only (Default: current UNIX epoch time)
• -v: Enables verbose program output
• -h: Prints help usage

Decrypt/Encrypt Command Line Arguments

Encrypt and decrypt share the same command line arguments detailed below:

• -i infile: Specifies input file as infile. (Default: stdin)
• -o outfile: Specifies outputfile as outfile. (Default: stdout)
• -n keyfile: Specifies public key file in case of encrypt and private key file in case of decrypt. (Default: ss.pub (encrypt) or ss.priv (decrypt))
• -v: Enables verbose program output
• -h: Prints help usage

To Run

The following is an example of how to encrypt a message in input.txt and output that encrypted message to encrypted_message.txt. It will then decrypt that encrypted message into output.txt. Other inputs will be default.

First, generate the keys:

./keygen

A 256 bit public/private key pair was created and put into ss.pub and ss.priv.

Then, encrypt the message in input.txt:

./encrypt -i input.txt -o encrypted_message.txt

Now an encrypted message is located in encrypted_message.txt.

Finally, decrypt that encrypted message and place the output into output.txt:

./decrypt -i encrypted_message.txt -o output.txt

Now the message in input.txt and output.txt are the same.