Privacy on Public Blockchain

We selected AES-256 as encryption algorithm because it's standard de-facto and well tested in multiple scenario.

By the way a good encryption algorithm can be useless if the implemented protocol has flaws.

In brief, AES-256 needs a strong key and a chaining method,the chaining method needs an init vector that should be random and never reused.

So we developed a function to encrypt data with a password/key. Here the code in Javascript/Nodejs for the encryption:

//function to encrypt a message by AES 256
async function encrypt_aes256(data,password){
    // pull the required libraries
    const {
        scryptSync,
        randomFillSync,
        createCipheriv
      } = await import('crypto');      
    // generate a random salt
    const saltbuffer = Buffer.alloc(16);
    const salt =randomFillSync(saltbuffer).toString('hex');
    // expand/derive password using a brute force attack algorithm
    const keybin = scryptSync(password, salt, 64);
    const key=keybin.toString('hex').substr(0,32);
    // generate a randmom init vector
    const ivbuffer = Buffer.alloc(8);
    const iv =randomFillSync(ivbuffer).toString('hex');
    // encrypt "data" by aes-256-cbc
    const cipher = createCipheriv('aes-256-cbc', key, iv);
    let encryptedData = cipher.update(data, "utf-8", "hex");
    encryptedData += cipher.final("hex");
    // return salt+iv+encrypted data in hex decimal string
    let r=salt+"#"+iv+"#"+encryptedData;
    return(r);
}

And Here the code in Javascript/Nodejs for the decryption:

// function to decrypt an ecrypted structure by Aes 256
async function decrypt_aes256(encrypteddata,password){
    // pull the required libraries
    const {
        scryptSync,
        createDecipheriv
      } = await import('crypto');
    // get fields from the encrypted data 
    const salt=encrypteddata.substr(0,32);
    const iv=encrypteddata.substr(33,16);
    const encryptedData=encrypteddata.substr(50);
    // expand key using the same salt of the origin
    const keybin = scryptSync(password, salt, 64);
    const key=keybin.toString('hex').substr(0,32);
    // decrypt data and convert to utf8 bytes
    const decipher = createDecipheriv('aes-256-cbc', key, iv);
    let clearData = decipher.update(encryptedData,"hex","utf-8");
    try{
        clearData += decipher.final("utf8");
    } catch(error){
        return(null);
    }
    // return decrypted data
    return(clearData);
}