**Asymmetric Encryption** also known as public key encryption is a type of encryption that uses two different keys for encryption and decryption. One key to encrypt the plaintext, and one key to decrypt the cyphertext. The encryption key(**Public Key**) is published so that anyone can encrypt a message. The decryption key(**Private Key**) is kept private, so that only the receiver/owner is able to decrypt the message.

The sender encrypts the message using his/her private key, then the message can be decrypted only using that sender’s public key, authenticating the sender. (Certificates)

The sender encrypts the message using receiver’s public key, then the message can be decrypted only using receiver’s private key. Only receiver can decrypt and read the message.

**Example A**, Bob makes public key A and private key A, and Cathrin makes public key B and private key B. Bob and Cathrin exchange their public keys. Now Bob can send an encrypted message to Cathrin by using Cathrin’s public key B. Cathrin uses her private key B to decrypt and read the message. If Cathrin wants to send an encrypted message to Bob, she uses Bob’s public key A to encrypt the message, which Bob can then decrypt with his private key A.

**Example B**, Bob makes public key A and private key A, and Cathrin makes public key B and private key B. Bob and Cathrin exchange their public keys. Now Bob can send a message to Cathrin by using his private key A to sign/encrypt his message. Cathrin uses Bob’s public key A to decrypt and read the message, she knows that the sender definitely is Bob. If Cathrin wants to send a signed/encrypted message to Bob, she uses her private key B to sign/encrypt the message, which Bob can then decrypt with Cathrin’s public key B. (Certificates)

**Popular Public Key Encryption Algorithms**

**RSA**

Designers: **Ron Rivest, Adi Shamir, Leonard Adleman**

Published:** 1978**

Certification:** PKCS#1, ANSI X9.31, IEEE 1363**

Key sizes: **1,024 – 4,096 bit **

**PGP**

Designers: **Phil Zimmermann**

Published:** 1991**

Key sizes: **1024 bit signature key, 4096 bit encryption key **

**DSA**

Designers: **NIST**

Published:** 1991**

Key sizes: **512 – 3072 bit **

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