Decrypt complete document in Salesforce

In my previous post I have written how to Encrypt a document, so here it is how to decrypt a document.

There are two ways to do it:

1. Without storing the decrypted document on cloud
2. Store it in decrypted form as an attachment.

Below are the codes for both of the things:

APEX:

//Using future method here to avoid CPU time limit exception

// Below method do not store anything on cloud and sends email with decrypted document to an 

// email Id

@future
public static void sendDecryptedAtt(String accId,Blob key, String emailId)
{

    List<Attachment> attList=[Select id,name,body from Attachment where parentId=:accId limit 1];


    if(attList.size() > 0){
        Blob decrypted = Crypto.decryptWithManagedIV('AES256', key, attList[0].body);
 
        String blobString=decrypted.toString();

        Blob doc=EncodingUtil.base64decode(blobString);
        String fileName=accAtt.name;

        sendEmail(doc,emailId,fileName);

        createAtt(doc, fileName, accId);
    }    
}

// below method sends email to the given email address
Public Static Void sendEmail(Blob attachmentFile, String emailId,String fileName)
{
    Messaging.EmailFileAttachment efa = new Messaging.EmailFileAttachment();
    efa.setFileName(fileName);
    efa.setBody(attachmentFile);

    Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
    email.setSubject('Decrypted File: '+ fileName);
    String[] emails=new List<String> {emailId};
    email.setToAddresses( emails);
    email.setPlainTextBody('Hi,\n\nPlease find attached decrypted document.\n\nThanks');

    email.setFileAttachments(new Messaging.EmailFileAttachment[] {efa});

    // Sends the email
    Messaging.SendEmailResult [] r = Messaging.sendEmail(new Messaging.SingleEmailMessage[ {email});
}

//Below method creates an attachment in the Salesforce with decrypted content

Public Static Void createAtt(Blob attachmentFile, String fileName, String accId)){

    Attachment att=new Attachment();

    att.name = 'Decrypted_'+fileName;
    att.body = attachmentFile;
    att.parentId = accId;

    insert att; 

}

Above code works for all kind of documents. Encryption technique is present in my previous posts.