rsa/crypto

Cryptographic algorithm using public key cryptosystem 🎉

Table of contents

• General Info
• Setup
• How to run
• Acknowledgements

General Information

RSA is an asymmetric cryptographic algorithm where each user has two keys

• private
• public

It uses data from the theory of numbers and in combination with the particularly large keys achieves encryption in a balance arithmetic that makes decryption by factorization impossible.

bn_sample_12.c

1. Create a private key¹

	Description
p	Prime
q	Prime
e	number
n	p * q
e,n	Public key
d	Private key

2. Message encryption

bn_sample_34.c

1. Message decryption
2. Message signing

bn_sample_5.c

1. Signature Verification

Setup

Large numbers bn² (multiprecision integer arithmetics) library provided by the openssl ³ For more information, you can check bn.

Check the virtual Ubuntu SEED machine 16.04.

1. Download SEEDUbuntu-v 16.04 from site

https://seedsecuritylabs.org/lab_env.html

2. Download and install VM engine from site

https://www.virtualbox.org/wiki/Downloads

3. Build a new VM os importing SEEDUbuntu

   • Select OS Type Linux ⁴ version Ubuntu

4. PRE-build VM hard disk from SEED file

• From the unzipped folder, select xxxx.vmdk where xxx is the SEED_name_version

5. Setting->General->Advanced

   • Shared Clipboard : Bidirectional
   • Drag'n'Drop : Bidirectional
   • Controller : VBoxVGA
   • Processor : 1+

6. Open terminal

$ sudo apt update
$ sudo apt install build-essential checkinstall zlib1g-dev -y
$ cd /usr/local/src/
$ wget https://www.openssl.org/source/openssl-1.0.2o.tar.gz
$ tar -xf openssl-1.0.2o.tar.gz
$ cd openssl-1.0.2o
$ ./config --prefix=/usr/local/ssl --openssldir=/usr/local/ssl shared zlib
$ make
$ make test
$ make install

7. Configure libraries

$ cd /etc/ld.so.conf.d/
$ vim openssl-1.0.2o.conf

8. Paste

$ /usr/local/ssl/lib

9. Reload link

$ sudo ldconfig -v

You can edit with atom or any other editor OpenSSL is installed in the '/usr/local/ssl' directory.

How to run

Any .c file can be executed as

gcc XXXXX -o XXXXXX.c -lcrypto

where XXXXX filename

Acknowledgments

• Assignment for cryptography

Footnotes

1. For simplicity, we use numbers 128 bits. Must be 512. ↩

2. BIGNUM can represent every great number, see https://www.openssl.org/docs/man1.0.2/man3/bn.html ↩

3. https://www.openssl.org ↩

4. Make sure install version ubuntu x32 architecture compatible with SEEDUbuntu. ↩