Diffie-Hellman or RSA? — TechKnowSurge

About this interactive

Public key cryptography solves a real problem: two parties who want to communicate securely but have never met, like your browser and a website you have never visited, have no pre-shared key. The lesson walked through the two most popular answers, Diffie-Hellman and RSA, named after the people who created them. Diffie-Hellman is a key exchange. Each side has a private key and they agree on some shared values in the open. Each side combines its private key with the shared values to make a public key, and they swap public keys. Each side then combines the other's public key with its own private key, and the math makes both arrive at the same result. That is two private keys, two public keys and a shared value, and nothing was ever encrypted along the way. The result is a shared key that can then be used for encryption. RSA uses one key pair: a public key anyone can have and a private key nobody else should. Whatever one key encrypts, only the other can decrypt. Encrypt a message with a server's public key and only that server can read it. If the server encrypts with its private key and you can decrypt with its public key, you know the message came from that server. That is why RSA can do encryption, identity checks, digital signatures and non-repudiation, not just key exchange. Both are asymmetric, both have keys that are safe to make public, both turn up inside protocols such as TLS, SSH and IPsec, and both are slow compared with symmetric encryption. That last point is why they are usually used just to get two sides to a shared key, so a symmetric cipher can carry the bulk of the data.

What you'll learn

Distinguish Diffie-Hellman from RSA by key structure: two private keys, two public keys and shared values against one public and private key pair
Distinguish their uses: Diffie-Hellman only exchanges a key, while RSA can encrypt, verify identity and support digital signatures
Recognize what the two share as public key cryptography: secure communication with no pre-shared key, usually to set up a symmetric key

Aligned to

ISC2 CC

5.1 Understand data security

CompTIA Security+

1.4 Explain the importance of using appropriate cryptographic solutions.

Cisco CCST Cybersecurity

1.4 Explain encryption methods and applications

Key terms

Diffie-Hellman: A key exchange algorithm that allows two parties to independently generate a shared secret over an insecure channel using two private keys, two public keys, and a shared value, without ever transmitting the secret itself.
RSA: An asymmetric encryption algorithm based on the difficulty of factoring large prime numbers, widely used for secure data transmission.
Public Key Cryptography: A cryptographic system that uses a mathematically linked public and private key pair to encrypt data and verify identity.
Public Key: A cryptographic key that can be shared openly and is used to encrypt data or verify digital signatures.
Private Key: A secret cryptographic key used in asymmetric encryption to decrypt data or create digital signatures.
Key Exchange: A method used to securely share cryptographic keys between parties over an insecure channel.
Pre-Shared Key: A shared secret passphrase used for authentication in wireless networks and VPNs without requiring a dedicated authentication server. In WPA-Personal mode, the PSK is used to derive the Pairwise Master Key (PMK) for encrypting the wireless session.

Topics

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