The key exchange algorithm is a method by which two or more parties can securely share a secret key used to encrypt and decrypt encrypted messages. This takes place over an open network, such as the internet, in a way that outsiders are unable to obtain information about the shared key.

The background of key exchange algorithms consists of mathematical problems that are easily solvable in one direction but practically impossible to reverse without a specific secret key. Thanks to this feature, parties can create a common secret key that only they know, even though communication takes place publicly.

Diffie-Hellman (DH) is the first published public key cryptography algorithm, enabling secure key exchange between two parties without the key itself passing through the communication channel. DH is based on the discrete logarithm problem and is widely used in many security protocols, such as TLS and VPN. The algorithm is vulnerable to "man-in-the-middle" attacks unless the identity of the parties can be reliably verified.

ECDH is a variant of the Diffie-Hellman key exchange that uses elliptic curve cryptography (ECC). It provides the same level of security as traditional DH with smaller key sizes, making it more efficient and faster. ECDH is a popular choice for mobile devices and IoT environments where device computational power and memory are limited.

RSA key exchange uses the RSA encryption algorithm to securely transfer the key between parties. One party generates a random encryption key, encrypts it with the other party's public RSA key, and then sends it to the other party, who can decrypt it with their private key. Although RSA key exchange is secure, it is typically slower than Diffie-Hellman based methods and is less commonly used for key exchange due to its high computational complexity.

## What is the Key Exchange Algorithm?

The key exchange algorithm is a method by which two or more parties can securely share a secret key used to encrypt and decrypt encrypted messages. This takes place over an open network, such as the internet, in a way that outsiders are unable to obtain information about the shared key.

### Operating principle

The background of key exchange algorithms consists of mathematical problems that are easily solvable in one direction but practically impossible to reverse without a specific secret key. Thanks to this feature, parties can create a common secret key that only they know, even though communication takes place publicly.

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## Common algorithms

### Diffie-Hellman key exchange (DH)

Diffie-Hellman (DH) is the first published public key cryptography algorithm, enabling secure key exchange between two parties without the key itself passing through the communication channel. DH is based on the discrete logarithm problem and is widely used in many security protocols, such as TLS and VPN. The algorithm is vulnerable to "man-in-the-middle" attacks unless the identity of the parties can be reliably verified.

### ECDH (Elliptic Curve Diffie-Hellman)

ECDH is a variant of the Diffie-Hellman key exchange that uses elliptic curve cryptography (ECC). It provides the same level of security as traditional DH with smaller key sizes, making it more efficient and faster. ECDH is a popular choice for mobile devices and IoT environments where device computational power and memory are limited.

### RSA key exchange

RSA key exchange uses the RSA encryption algorithm to securely transfer the key between parties. One party generates a random encryption key, encrypts it with the other party's public RSA key, and then sends it to the other party, who can decrypt it with their private key. Although RSA key exchange is secure, it is typically slower than Diffie-Hellman based methods and is less commonly used for key exchange due to its high computational complexity.


Key exchange algorithms

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MD5 hash - a broken classic

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Key exchange algorithms

What is the Key Exchange Algorithm?

Operating principle

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