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Table of contents
1.
Introduction
2.
What Is A Cryptographic Key
3.
Why is Key Updating Done in Cryptography
4.
Key Updating Process
4.1.
Diffie-Hellman Key Exchange Algorithm
4.2.
Key Derivation Function Method 
5.
Frequently Asked Questions 
5.1.
Explain the significance of a cryptographic key.
5.2.
How does Diffie-Hellman KAS work?
5.3.
Why should we update the keys on a regular basis?
5.4.
What is the main disadvantage of the Diffie-Hellman KAS Method?
5.5.
What is the encrypted data called in cryptography?
6.
Conclusion
Last Updated: Mar 27, 2024

What Are Key Updating In Cryptography?

Author Geetika Dua
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Introduction

Do you know what cryptography is? Do you have a keen interest in exploring different aspects of key updating cryptography? Don’t worry! We got you covered. 

introduction

In this blog, let us explore the concept of key updating in cryptography. Keep Reading!

What Is A Cryptographic Key

A cryptographic key is defined as the string that is used as the basis of the encryption algorithm. It alters the accurate information and converts it into an encrypted form. Only and only the person who has access to the decrypted key can unlock the data and understand this; this is highly important for the security of cryptography.

Jumping on to the technical terms of cryptography, the Original data is called the plaintext, and the final data after encryption is referred to as ciphertext.

We can write the formula for this conversion as

PlainText+ key = CipherText

Cryptographic Key
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Why is Key Updating Done in Cryptography

Another question that may arise in your mind is the need to update the key after a process concludes constantly. Why is key updating done? What is the need to do key updating?

There is a need to do so because of security reasons. Previously used keys can be less secure. Therefore they can be determined by unauthorized users easily. It is advisable to update the keys on a regular basis to ensure perfect forward secrecy.

Key Updating Process

Let us now look at the process of updating the keys in cryptography.

How to update the keys?

Diffie-Hellman Key Exchange Algorithm

A famous method to solve this problem is the use of Diffie-Hellman. We make and update the key regularly. There exists no relationship between the old and new keys.

The Diffie-Hellman Method requires extensive operations like exponentiations. Exponentiation is the mathematical process of raising one quantity to the power of another. Therefore, we apply more accessible methods of updating the key.

The basic idea or process is as follows-

  • The sender selects new public and private keys when User X sends a message to User Y (or vice versa).
     
  • It sends the new public key and a message encrypted under the old Diffie-Hellman key. The  Diffie-Hellman key used by the recipient is computed from the new public key and the recipient’s old private key.
     
  • If User X and User Y used a Diffie-Hellman to compute a new key every time a message is sent, they would each have to perform two exponentiations per message sent.

    • Imagine there are two discrete keys, A and B.
       
    • Each of them will first compute their public key. After exchanging public keys, they calculate the shared private key.

Key Derivation Function Method 

The second primary type of key updating or key ratcheting incorporated into Signal uses a key derivation function denoted by KDF. The function KDF has two inputs and two outputs. The two inputs are

 1. A constant value C, and

 2. A KDF(Key Derivation Function) key
 

An output key, denoted by OKi+1. We represent this process by notating KDF(C, Ki) = (Ki+1, OKi+1). KDF is used to construct a KDF chain iteratively. This requires an initial KDF key K0. Then a sequence of output keys is produced as follows: 

KDF(C, K0) = (K1, OK1) 

KDF(C, K1) = (K2, OK2) 

KDF(C, K2) = (K3, OK3)

Generally, a key derivation function (KDF) takes an input, runs it through a particular function, and outputs secure keying material. The input may be a password or other weak keying material.

Frequently Asked Questions 

Explain the significance of a cryptographic key.

A cryptographic key is defined as the string that is used as the basis of the encryption algorithm. It alters the accurate information and converts it into an encrypted form. 

How does Diffie-Hellman KAS work?

The Diffie-Hellman Method requires extensive operations like exponentiations. We make and update the key regularly. There exists no relationship between the old and new keys.

Why should we update the keys on a regular basis?

There is a need to do so because of security reasons. Previously used keys can be less secure. Therefore they can be determined by unauthorized users easily.

What is the main disadvantage of the Diffie-Hellman KAS Method?

The Diffie-Hellman Method requires extensive operations like exponentiations. Therefore, we apply more accessible methods of updating the key.

What is the encrypted data called in cryptography?

The encrypted data is called the CipherText. Only the person with access to the decryption key can decode and understand the plain text.

Conclusion

This blog studied the concept of keys and updating them in cryptography. We hope you got clarity on this topic. Want to know more about this topic? Have a look at our other blogs.

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