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file encryption

Requirements​

  • OpenSSL
  • Linux remote servers

Symmetric Encryption​

Uses single shared key for encryption/decryption

  • Server A: Encrypts
  • Server B: Decrypts

Step 1: Generate Key (Server A)​

openssl rand -out secret.key 32
  • Generate a random key for encryption
  • The key should be 256 bits (32 bytes) which is the standard size for AES-256 encryption

Step 2: Create File (Server A)​

echo "This is a simple line of code" > text.txt

Step 3: Encrypt File (Server A)​

openssl enc -aes-256-cbc -pbkdf2 -in text.txt -out text_encrypted.dat -pass file:./secret.key
  • Use the above secret.key to encrypt the text.txt

Step 4: Transfer to Server B​

scp text_encrypted.dat secret.key [email protected]:/home/abc/
  • Use SCP (assuming Server B IP: 52.221.181.100, username: abc)
tip

Use SSH/SCP for secure transfer, avoid manual passwords

Step 5: Decrypt File (Server B)​

openssl enc -d -aes-256-cbc -pbkdf2 -in text_encrypted.dat -out text_decrypted.txt -pass file:./secret.key
  • Use the secret key to decrypt the file

Drawbacks​

While symmetric encryption is fast and efficient, it does have some drawbacks, especially when it comes to key distribution and security

  • Key sharing insecure in large systems
  • Intercepted key compromises all data

Asymmetric Encryption​

Uses public/private key pairs for secure communication

  • Server: Generates keys, shares public key
  • User: Generates keys, shares public key
  • Encrypt with recipient's public key; decrypt with own private key

User to Server

Step 1: Generate Keys​

Server

openssl genpkey -algorithm RSA -aes256 -out server_private_key.pem
openssl rsa -pubout -in server_private_key.pem -out server_public_key.pem

User

openssl genpkey -algorithm RSA -aes256 -out user_private_key.pem
openssl rsa -pubout -in user_private_key.pem -out user_public_key.pem

Step 2: Exchange Public Keys​

User to Server (Server IP: 52.221.181.100, username: abc)

scp user_public_key.pem [email protected]:/home/abc/

Server to User

scp server_public_key.pem user@UserIP:/path/to/user/  # Adjust UserIP/path

Step 3: User Encrypts File​

echo "Is this correct?" > user_text.txt
openssl pkeyutl -encrypt -inkey server_public_key.pem -pubin -in user_text.txt -out user_text_encrypted.dat

Step 4: User Transfers to Server​

scp user_text_encrypted.dat [email protected]:/home/abc/

Step 5: Server Decrypts​

openssl pkeyutl -decrypt -inkey server_private_key.pem -in user_text_encrypted.dat -out user_text_decrypted.txt
  • Use server_private_key.pem to decrypt the file

Step 6: Server Encrypts Response​

echo "This is correct!" > server_text.txt
openssl pkeyutl -encrypt -inkey user_public_key.pem -pubin -in server_text.txt -out server_text_encrypted.dat

Step 7: Server Transfers to User​

scp server_text_encrypted.dat user@UserIP:/path/to/user/  # Adjust UserIP/path

Step 8: User Decrypts​

openssl pkeyutl -decrypt -inkey user_private_key.pem -in server_text_encrypted.dat -out server_text_decrypted.txt
  • Use user_private_key.pem to decrypt the file
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