What is Cryptography? – Cryptography Explained – AWS

Asymmetric (or public-key)cryptography consists of a broad set of algorithms. These are based on mathematical problems that are relatively easy to perform in one direction, but which cannot be easily reversed.

One famous example of this type of problem is the factoring problem: for carefully chosen prime numbers p and q, we can compute the product N=p*q quickly. However, given only N, it is very hard to recover p and q.

A common public-key cryptographic algorithm based on the factoring problem is the Rivest-Shamir-Adleman (RSA) function. When combined with an appropriate padding scheme, RSA can be used for multiple purposes, including asymmetric encryption.

An encryption scheme is calledasymmetricif it uses one keythe public keyto encrypt data, and a different but mathematically related keythe private keyto decrypt data.

It must be computationally infeasible to determine the private key if the only thing one knows is the public key. Therefore, the public key can be distributed broadly while the private key is kept secret and secure. Together the keys are referred to as akey pair.

One popular asymmetric encryption scheme is RSA-OAEP, which is a combination of the RSA function with the Optimal Asymmetric Encryption Padding (OAEP) padding scheme. RSA-OAEP is typically only used to encrypt small amounts of data because it is slow and has ciphertexts which are much larger than the plaintext.

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What is Cryptography? - Cryptography Explained - AWS