Asymmetric encryption, also known as public-key cryptography, is a type of encryption that uses a pair of keys to encrypt and decrypt data. The pair of keys includes a public key, which can be shared with anyone, and a private key, which is kept secret by the owner. In asymmetric encryption, the sender uses the recipient’s public key to encrypt the data. The recipient then uses their private key to decrypt the data. This approach allows for secure communication between two parties without the need for both parties to have the same secret key. RSA is one of the most commonly used asymmetric encryption algorithms. It is based on the mathematical problem of factoring large numbers, which is believed to be hard to solve. RSA stands for Rivest-Shamir-Adleman, the names of the three inventors of the algorithm. RSA can be used for both encryption and digital signatures. To generate an RSA key pair, the following steps are performed:

Choose two large prime numbers, p and q, and compute their product, n = pq. This is called the modulus.

Choose a small number, e, that is relatively prime to (p-1)(q-1). This is called the public exponent.

Compute a number, d, that satisfies the equation ed ≡ 1 (mod (p-1)(q-1)). This is called the private exponent.

The public key is (n, e) and the private key is (n, d).

To encrypt a message, m, with the public key (n, e), the following formula is used:

c = m^e mod n

To decrypt a ciphertext, c, with the private key (n, d), the following formula is used:

m = c^d mod n

References :=

[Implementing and Operating Cisco Security Core Technologies (SCOR) v1.0], Module 3: VPN Technologies, Lesson 3.1: Site-to-Site VPNs, Topic 3.1.2: IPsec VPNs

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