Encrypt-Decrypt-with-OpenSSL-RSA

What is OpenSSL ?

OpenSSL is opensource library that provide secure communication over networks using TLS (Transfer Secure Layer) and SSL (Secure Socket Layer). It supports many cryptographic algorithm AES, DSA, RSA, SHA1, SHA2, MD5.. More information about OpenSSL

What is RSA ?

RSA is algorithm using for encrypting and decrypting data. It is in the class of asymmetric cryptographic algorithm (public key cryptography). Asymmetric cryptographic algorithm has two different keys. They are public key and private key. Public key is given everyone. Private key is secret. Data is encrypted by public key then decrypted by private key. More information about RSA Algorithm

Steps of RSA Algorithm

1 - Define two different prime numbers. ( p and q)
2 - Calculate modulus for private key and public key. n = p * q
3 - Caluclate totient. Q(n) = (p -1) * (q -1)
4 - Define public key exponent (e). e must be in 1 < e < Q(n). e and Q(n) are relatively prime.
5 - Define private key exponent (d). It must be secret. d*e = 1 + kQ(n). d must be in 1 < d < Q(n)

Encrypt Message

c = m^e mod (n)

Decrypt Message

m = c^d mod (n)

Sample

1 - p = 3 and q = 11
2 - modulus n = 3 * 11 = 33
3 - totient Q(n) = (3 - 1) * (11 - 1) = 20
4 - 1 < e < 20 and e = 7
5 - de mod Q(n) = 1 and 7d mod 20 = 1, d = 3

Message can be 4. m = 4
Encrypt message: c = 4^7 mod (33) = 16384 mod (33) and c = 16. Encrypted message is 16
Decrypt message: m = 16^3 mod (33) = 4096 mod (33) and m = 4. Decrypted message is 4

Project Code

This project encrypts and decrypts message in a simple way. Let's examine openssl_rsa.h file.

create_RSA function creates public_key.pem and private_key.pem file. Public_key.pem file is used to encrypt message. Private_key.pem file is used to decrypt message.

public_encrypt function encrypts message using public_key.pem file

private_decrypt function decrypts encrypted message using private_key.pem

create_encrypted_file function creates encryted file as .bin file.

Compilation Process

For compile the entire project

 make

For clean the project directory

 make clean

For clean the project directory and remove generated files during execution

 make deep_clean

Docker build and run

For docker build to create an image named opensslapp

docker build --tag opensslapp .

For run image as container

docker run -i -t --rm opensslapp