Hybrid Encryption and Decryption Explained: Securing Data with AES-256 and RSA (Step-by-Step Guide)

 

Introduction

Hybrid Encryption Explained: Securing Data with AES-256 and RSA (Step-by-Step Guide)

In the previous post we have seen Advanced Encryption Standards 256. AES256 is a symmetric algorithm used for encryption and decryption based on a shared secret key. Besides secret key, there are other parameters that need to be set for specifying the key bits, the padding bits and the mode of encryption/decryption.

Let’s now dive deeper into the security. So here we are going to discuss the hybrid encryption and decryption process to enhance the security a step further. This process utilizes both Symmetric Key algorithm and Asymmetric Key algorithm and hence the term hybrid. The idea behind the hybrid encryption and decryption is that we use symmetric algorithm to encrypt the data using a secret key. Now, this key needs to be shared with the receiver in order for him to decrypt the data. So, instead of sharing the key in plain text format, this key itself is encrypted using the asymmetric algorithm with the public key of the receiver. Now, no one other than the intended receiver will be able to decrypt the encrypted secret key using his own private key, as his own public key is used to encrypt the secret key.

Why only Symmetric Algorithm AES256 to encrypt the data and RSA to encrypt the shared Key?

To combine the bulk speed of symmetric encryption with the secure key exchange of asymmetric encryption.

Symmetric Algorithm:

This is the simplest and best-known encryption technique which uses a shared secret key for both encryption and decryption. Since the idea behind the symmetric algorithm is less complex, it executes faster, and is the preferred technique for the transmission of bulk data.

The Plain Text is encrypted using the key and the same key is used for decryption of Cipher Text to retrieve the Plain Text. The key is shared by some external medium. Most common symmetric algorithms are DES, AES-128, AES-192 and AES-256.

The sharing of key by external medium can be considered as one of the main disadvantage of Symmetric Algorithm. If this external medium has been tampered, then the key gets compromised and the whole idea of security is lost.

Asymmetric Algorithm:

This encryption algorithm is relatively complex as compared to Symmetric Algorithm and is considered to be more secure than Symmetric Algorithm as it uses to two different keys for encryption and decryption. The encryption is done by Public Key and decryption is done by the corresponding Private Key.

It is also referred to as Public Key Cryptography. The Public Key used for encryption is known to all and the Private Key used for decryption is kept confidential. The encryption and decryption are done by the Public Key and Private Key of the same user.

RSA (Ron Rivest, Adi Shamir, Leonard Adleman), the acronym of the surname, is widely used asymmetric algorithm.

Digital Certificate are used to discover public keys. There are different tools and techniques to generate public key and private key.

Note that Key Size in Symmetric Algorithm is very small as compared to the Key Size in Asymmetric Algorithm. Hence, asymmetric algorithm is much slower than symmetric algorithm.

Hybrid Encryption Process

Symmetric Encryption

For encryption of the data, AES-256 is used which uses a 256 bits Key and 128 bits block with CBC (Cipher Block Chaining) Mode and PKCS7 (Public Key Cryptography Standard 7) padding.

 

Asymmetric Encryption

Asymmetric encryption algorithm RSA, is used for the encryption of the Key (used in symmetric encryption AES-256). This Symmetric Key is encrypted using the public key of the recipient.

The encrypted data from Symmetric Encryption and encrypted key from Asymmetric Encryption are then shared with the third party.

 

Hybrid Asymmetric Encryption Process

Hybrid Decryption Process

Asymmetric Decryption

Asymmetric algorithm RSA is used for decryption of the encrypted secret key. The receiver of the encrypted data and encrypted secret key will first have to decrypt the secret key using his own private key (contained in Private.pfx certificate file). The key is now in plain text and can be used to decrypt the data using symmetric decryption.

Hybrid Asymmetric Decryption Process

Symmetric Decryption

Using the (plain text) key from asymmetric decryption, the receiver will now decrypt the encrypted data via AES256 decryption.

Hybrid Decryption using Key and IV

A complete breakdown of all the acronyms used in the blog post and cryptography analysis, along with their full forms and brief roles:

Acronym	Full Form	Description / Context
AES	Advanced Encryption Standard	A widely adopted symmetric block cipher algorithm. AES-256 uses a 256-bit key length for maximum security.
RSA	Rivest-Shamir-Adleman	An asymmetric encryption algorithm named after its inventors: Ron Rivest, Adi Shamir, and Leonard Adleman.
DES	Data Encryption Standard	An older symmetric encryption standard introduced in the 1970s, now obsolete and replaced by AES.
CBC	Cipher Block Chaining	A mode of operation for block ciphers where each block of plaintext is XORed with the previous ciphertext block before being encrypted.
PKCS (PKCS#7)	Public Key Cryptography Standards	A set of security standards defined by RSA Laboratories. PKCS#7 specifies data syntax and padding rules to align data blocks in block ciphers.
IV	Initialization Vector	A random, non-secret data block used alongside a secret key in modes like CBC. It ensures identical plaintexts yield completely different ciphertexts when encrypted twice.
PFX	Personal Information Exchange	A standard file format extension (.pfx, precursor to .p12) used to bundle private keys along with their associated public key certificates into a single password-protected file.

Note: 

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