What is the combination of a public key and a private key known as?

One of the weaknesses some point out about symmetric key encryption is that two users attempting to communicate with each other need a secure way to do so; otherwise, an attacker can easily pluck the necessary data from the stream. In November 1976, a paper published in the journal IEEE Transactions on Information Theory, titled "New Directions in Cryptography," addressed this problem and offered up a solution: public-key encryption.

Also known as asymmetric-key encryption, public-key encryption uses two different keys at once -- a combination of a private key and a public key. The private key is known only to your computer, while the public key is given by your computer to any computer that wants to communicate securely with it. To decode an encrypted message, a computer must use the public key, provided by the originating computer, and its own private key. Although a message sent from one computer to another won't be secure since the public key used for encryption is published and available to anyone, anyone who picks it up can't read it without the private key. The key pair is based on prime numbers (numbers that only have divisors of itself and one, such as 2, 3, 5, 7, 11 and so on) of long length. This makes the system extremely secure, because there is essentially an infinite number of prime numbers available, meaning there are nearly infinite possibilities for keys. One very popular public-key encryption program is Pretty Good Privacy (PGP), which allows you to encrypt almost anything.

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The sending computer encrypts the document with a symmetric key, then encrypts the symmetric key with the public key of the receiving computer. The receiving computer uses its private key to decode the symmetric key. It then uses the symmetric key to decode the document.

To implement public-key encryption on a large scale, such as a secure Web server might need, requires a different approach. This is where digital certificates come in. A digital certificate is basically a unique piece of code or a large number that says that the Web server is trusted by an independent source known as a certificate authority. The certificate authority acts as a middleman that both computers trust. It confirms that each computer is in fact who it says it is, and then provides the public keys of each computer to the other.

Private Key and Public Key form the encryption that’s used to encode information in an SSL certificate. As such, they help encrypt and protect users’ data and information.

These keys are created using RSA, DSA, ECC (Elliptic Curve Cryptography) algorithms. The strength and security of both public and private keys are decided by the key size, i.e., the bit-length. Currently, the strongest industry standard is a 2048-bit RSA key.

But how do public key and private key differ from each other? Which one should you prefer? In this article, we’ll help you understand both Private Key and Public Key with relevant examples.

What is Private Key?

Private Key is the secret key used to encrypt and decrypt messages between communicators. It’s a form of symmetric encryption, i.e., the same key is utilized for both encryption and decryption purposes.

The biggest drawback here is the potential loss of the private key. If it’s lost, the system is rendered void. To mitigate that drawback, PKI (public key infrastructure) is used. This is essentially a combination of both private and public key, so a loss in private key doesn’t affect the system.

Example: A encrypts sensitive information into ciphertext using the private key and shares it with B. In order to access the information, B must decrypt the ciphertext into plain text using their copy of the private key.

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What is Public Key?

Public Key functions on the basis of asymmetric encryption. An asymmetric encryption functions on the basis of both public and private key.

The messenger encrypts the message using the public key, and the receiver can access the message after decrypting it with their private key. Security is ensured because only the person with the relevant private key can decode the message. As such, even if third-party access the information, the data remains confidential.

The public key is made available through the public accessible directory.

Example: A encrypts sensitive information using B’s public key and sends it across. B can only access that information and decrypt it using their corresponding private key.

Private Key and Public Key: The Differences

Private KeyPublic KeySymmetric encryption.Asymmetric encryption.Remains in the confidential use of two individuals.Available to everyone through the publicly accessible directory.The possibility of key getting lost, which will render the system void.Key is publicly held so no possibility of loss.

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