Cryptography

Keywords

Ciphertext - Represent the plaintext encrypted

Cipher - A method of encrypting or decrypting data. Modern ciphers are cryptographic, but there are many non cryptographic ciphers like Caesar.

Plaintext - It’s a text or file not encrypted

Encryption - Processing for encrypting data into ciphertext, using a cipher.

Encoding - NOT a form of encryption, just a form of data representation like base64. Immediately reversible.

Key - Information for encrypting and decoding the encrypted data

Passphrase - Separate to the key, a passphrase is similar to a password and used to protect a key.

Asymmetric encryption - Uses different keys to encrypt and decrypt.

Symmetric encryption - Uses the same key to encrypt and decrypt

Standards PCI-DSS specify how your data need to be encrypted in the storage (in rest) and while they are being transmitted.

https://listings.pcisecuritystandards.org/documents/PCI_DSS_for_Large_Organizations_v1.pdf

Types of encryption

Symmetric encryption, we have one key for encrypting and decrypting. DES (Data Encryption Standard), not used, 3DES or AES (Advanced Encryption Standard) are algorithms of symmetric encryption.

Asymmetric encryption, it’s a pair of keys. One to encrypt (private key) and the other one to decrypt (public key). RSA or Elliptic Curve Cryptography

RSA

RSA is an asymmetric key

SSH

It’s possible to crack the password with john:

python3 ssh2john.py ~/idrsa.id_rsa > ~/idrsa_cracked
./john --wordlist ../../rockyou.txt ~/idrsa_cracked

Diffie-Hellman

When two people which to communicate securely in the public channel, they need to exchange their key and to have an common key. For doing that, we use the Diffie-Hellman:

https://ee.stanford.edu/~hellman/publications/24.pdf

https://www.youtube.com/watch?v=NmM9HA2MQGI