The simplest form of encryption is called symmetric key encryption. When we want to encrypt a file, we use a key and we send that encrypted file to someone, than they have to have the same key to open a file. Basically, the receiver of the encrypted file has to enter the same key you have to enter to encrypt the file. The key must be identical with this kind of file encryption. This simple form of encryption is also known as secret, or private, key encryption. This kind of file encryption is very good for encrypting a large amount of data, and it is also very fast. There are algorithms that are considered to be symmetric algorithms and they use symmetric key encryption.
However, symmetric key encryption has some disadvantages. For instance, if you send someone encrypted message via email, they have to have a key to decrypt it. Key exchange is a problem, how you send a key securely to a receiver without someone intercepting it? The other problem is, if you want your encrypted file to be opened by few people and you share the same key that is not very secure, because the key could be leaked out much easier when large group of people use the same key. The solution of using different key password for each receiver is not very practical, too.
Asymmetric key encryption uses two keys, one is called the private key, other is called the public key. We keep the private key secretly for ourselves only, and public key is accessible to anyone. This form of file encryption is also known as "public key" cryptography. Those two keys are not the same key, they are mathematically related but they are not the same. Anyone with your public key can encrypt a message to you - but only you can encrypt it with the private key. To exchange two way encrypted messages two sets of public/private key pairs are needed. Public key encryption solves the problem of key exchange, meaning the only keys handed out are public. Public key encryption is often used in digital certificates and signatures. However, the disadvantages of public key encryption is that it is very slow and it does not encrypt large amounts of data very well.
Hybrid encryption is a combination of symmetric and asymmetric key encryption. In this method we take the recipients public key and encrypt the symmetric or secret key only, which is a very small amount of data. The recipient must have a private key to decrypt a file, using the private key the recipient gets the synthetic key to open, or read a large amount of data, which would not be feasible to encrypt with classic asymmetric key encryption. Hybrid encryption overcomes the shortcomings of other two forms of encryption by combining them both.
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