AES encryption, what are public and private keys?

Question

As others have said, AES is a symmetric algorithm (private-key cryptography). This involves a single key which is a shared secret between the sender and recipient. An analogy is a locked mailbox without a mail slot. Anybody who wants to leave or read a message needs to have a key to the mailbox.

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Public-key cryptography involves two related keys for each recipient involved - a private key which is a secret known only by the recipient, and a related public key which is known by all senders.

The sender encrypts the message using the recipient's public key. That message can only be decrypted by a recipient with a private key matching the public key.

An analogy for public-key encryption is a locked mailbox with a mail slot. The mail slot is exposed and accessible to the public. Its location (the street address) is the public key. Anyone knowing the street address can go to the door and drop a written message through the slot. But only the person who possesses the private key can open the mailbox and read the message.

AES is a symmetric algorithm, so it does not have public and private keys - only a shared secret.

In the simplest form:

AES is a symetric algorithm, it uses the same key for encryption and decryption.So tat whoever has the key can read your message.

The private and public key is for Asymetric alogorithms like RSA, normally people use public key to encrypt and private key to decrypt( only HMAC or MAC will use private key to encrypt, and public key to decrypt).The public key is known to everyone, the private key is only known to yourself, so no one can read the message sent to you.

I do not know how the .net framework specifically works (the question should probably have been tagged .net) but by your question it sounds like it implements public/private key crypto, just using AES for its symmetric component.

The usual mode of doing public key encryption is to

• Generate a symmetric key
• Encrypt the data with this key, using a symmetric algorithm like AES.
• Encrypt the symmetric key with the public key, using a asymmetric algo like RSA.
• Bundle the encrypted sym key with the encrypted data

The reason symmetric algos are preferred for the data itself is that asymmetric ones are very slow.

Given that they couldn't test security (all they really had was the absense of breaks, for several og the candidates), the reason for choosing Rijndael for AES was (mostly) performance related.