Nøkkelveksling

Nøkkelveksling, often translated as key exchange, is a cryptographic method used by two parties to establish a shared secret key over an insecure communication channel. This shared secret can then be used for symmetric encryption, providing confidentiality and integrity for subsequent communications. Without a secure way to agree on a key, two parties cannot engage in secure communication using symmetric algorithms, as they would have no common secret to use for encryption and decryption.

The most well-known algorithm for nøkkelveksling is the Diffie-Hellman key exchange. In this method, both parties agree on public parameters: a prime number p and a generator g. Each party then chooses a private secret number, say a and b, respectively. They compute public values A = g^a mod p and B = g^b mod p, and exchange these public values. Party 1 can then compute the shared secret S = B^a mod p, and Party 2 can compute S = A^b mod p. Both calculations result in the same shared secret S, which can then be used for encryption.

Another approach to nøkkelveksling involves public-key cryptography. In this scenario, one party might have a public key that others can use to encrypt messages intended for them, and a corresponding private key that only they possess to decrypt these messages. To establish a shared secret, one party could encrypt a randomly generated secret key using the other party's public key. The intended recipient then uses their private key to decrypt this secret key, thus establishing a shared secret without prior direct communication of the key itself.

Nøkkelveksling is a fundamental building block in many secure communication protocols, including Transport Layer Security (TLS), which secures web browsing. It is essential for establishing the secure foundations upon which modern encrypted communications are built.