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The difference between public key and private key cryptography

10 Aug, 2021 Eduardo Ricou
The difference between public key and private key cryptography

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The key element of any blockchain project is the cryptography used to protect data. Without it, no transactions are protected. The cryptocurrencies we all know are built on so-called public key cryptography. In this article, we'll look at the difference between public key cryptography and private key cryptography, discuss each system's advantages and disadvantages, and answer other questions on this topic.

What are public and private key cryptography?

There are two basic concepts in cryptography: encryption and decryption. Encryption is the transformation of the original message into an unreadable, i.e., encrypted one. Decryption is the conversion of an encrypted message back to its original form. An algorithm and key are used for both encryption and decryption, and there are two methods of encryption and decryption: symmetric and asymmetric encryption. Symmetric encryption, also called private key encryption, has been known to humanity for a very long time. On the other hand, asymmetric encryption, also called public key encryption, appeared only in the 1970s and became really widespread as the Internet developed.

Bitcoin public and private key examples

What is private key encryption?

Private key encryption is a very popular, simple and effective encryption system. It allows both encryption and decryption to be performed using the same key. Since anyone who has the key can decrypt information encrypted in this way, this key must be kept secret and accessible only to the sender and the recipient of the information. This is why it's called a private key, and the encryption system itself is called private key encryption.

What is public key encryption?

This encryption system is much more complex, using the private key only to decrypt the message. To encrypt the same message, a separate public key derived from the public key is used. If a person knows the private key, they can calculate the public key. However, knowing only the public key isn't enough to calculate the private key. That's why the public key doesn't need to be kept secret since knowing it doesn't allow encrypted information to be decrypted.

How does public and private key encryption work?

In private key cryptography, the sender encrypts the message using the private key and sends it to the recipient. For the recipient to decrypt the message, they'll need the sender to provide the same private key through a well-secured channel, thus reducing the security of such cryptographic systems.

Private key cryptography

In public key cryptography, the message sender encrypts the message with the public key and sends it to a recipient. The message recipient receives it and decrypts it with the private key that only he or she has. Since only the recipient needs a private key in this encryption system, it doesn't have to be sent, thus increasing its security. In public key cryptography, only the recipient — not even the sender — can decrypt the message.

Public key cryptography

The advantages and disadvantages of public key cryptography

Let's see the advantages and disadvantages of these encryption systems by comparing them.

Comparison of private and public key cryptography

<.td>

Private key cryptography

Public key cryptography

Encryption-decryption speed

Faster

Slower

Required computing power

Less

More

Need to send a private key via a secure channel

Yes

No

Key length

Shorter

Longer

Parties who need to know the private key

Recipients and senders

Recipients only

Complexity of key management in a large network

High

Low

Able to be used to generate an electronic digital signature

No

Yes

In this comparison, we see that although private key encryption is much simpler and faster, it's not a suitable option for blockchain networks.

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