Research Article

# Improved Encrypted-Signals-Based Reversible Data Hiding Using Code Division Multiplexing and Value Expansion

## Algorithm 1

 Preprocess and signal encryption phase Input:An original image with a size of , the number of spreading sequences , the expanded parameter , and public key . Output:The encrypted unit . Step  1:Obtain the separated signals from the original pixel , , which can be calculated in Section 3.1. Define the embedded vector , and each pixel unit is represented as . Step  2:Modify to be by formula (14) for preventing overflow. Step  3:Encrypt by and generate an encrypted unit . Data embedding phase Input:The encrypted unit , the number of spreading sequences , the expanded parameter , public key , and secret bits. Output:Marked unit . Step  1:Divide secret bits into two parts and , where contains secret bits and contains the remaining bits. Step  2:Transform secret bits , in to using formula (9), and then obtain the compound sequence for each unit . Step  3:Encrypt by and denote it as . Step  4:Embed into using CDM. By formula (10), obtain a new vector . Step  5:Encode secret bits in to . is the decimal of for each unit . Step  6:Encrypt by and denote it as . Step  7:Embed into using VE. By formula (15), obtain a new signal . Then, generate a marked unit . Data extraction and image recovery phase Input:The marked unit , the number of spreading sequences , the expanded parameter , and private key . Output:Secret bits and the original image. Step  1:Decrypt using to generate . Step  2:Extract secret bits from by formulas (9) and (12). Step  3:Obtain by extracting LSBs of . Step  4:Calculate by formula (16) and recover by formula (17). Step  5:Recover the original image by calculating .

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