HTTP

HTTP is what the internet runs on.

HTTP is unencrypted, which allows people to intercept packets and read them. This is a Man in the middle attack (MITM).

Symmetric Encryption

• Symmetric Encryption involves using the same key to both encrypt and decrypt the data.
• One caveat means that this must be shared somehow previously.
• This is much faster than Asymmetrical Encryption, and is commonly implemented with AES.

Asymmetric Encryption

• Asymmetric Encryption relies on two keys, a public and private key to encrypt and decrypt data.
• Data encrypted with the public key can only be decrypted by the private key.
• A common algorithm is RSA, which uses two random prime numbers for the public and private key:

int x = 61, int y = 53;
int n = x * y;
// n = 3233.

// compute the totient, phi
int phi = (x-1)*(y-1);
// phi = 3120.

int e = findCoprime(phi);
// find an 'e' which is > 1 and is a co-prime of phi.
// e = 17 satisfies the current values.

// Using the extended euclidean algorithm, find 'd' which satisfies
// this equation:
d = (1 mod (phi))/e;
// d = 2753 for the example values.

public_key = (e=17, n=3233);
private_key = (d=2753, n=3233);

// Given the plaintext P=123, the ciphertext C is :
C = (123^17) % 3233 = 855;
// To decrypt the cypher text C:
P = (855^2753) % 3233 = 123;

TLS

• TLS stands for Transport Layer Security, which is a security protocol that runs over HTTP to achievee secure communication online.

SSL Certificate

• A trusted entity that signs digital certificates, (SSL Certificates) that are used to verify authenticity online.

TLS Handshake

• The client sends a client hello—a string of random bytes—to the server.
• The server responds with a server hello—another string of random bytes—as well as its SSL certificate, which contains its public key.
• The client verifies that the certificate was issued by a certificate authority and sends premaster secret—yet another string of random bytes, this time encrypted with the server's public key—to the server.
• The client and the server use the client hello, the server hello, and the premaster secret to then generate the same symmetric-encryption session keys, to be used to encrypt and decrypt all data communicated during the remainder of the connection.

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