Creating Cipher with IV inconsistent behaviour

[jithinsk]

• Version: 13.0.1
• Platform: Linux WORKPC 4.15.0-72-generic fs: fix fd leak on early readstream destroy node#81-Ubuntu SMP Tue Nov 26 12:20:02 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
• Subsystem: crypto

I have been trying to encrypt and decrypt text using crypto package. I was able to implement it successfully. Below is my code for the same:

const algorithm = 'aes-128-cfb';
const iv = crypto.randomBytes(16);
const key = 'dq14Bopnw1A1FaUi';

//Concatenating iv before cipher.update
function encrypt(text) {
    let cipher = crypto.createCipheriv(algorithm, key, iv);
    text = Buffer.concat([Buffer.from(iv), Buffer.from(text)]);
    let encrypted = cipher.update(text);
    encrypted = Buffer.concat([encrypted, cipher.final()]);
    return encrypted.toString('base64');
}

//Decrypting text
function decrypt(base64Encoded) {
    let decodedData = Buffer.from(base64Encoded, "base64").toString('hex');
    let decodedIV = new Buffer.from(decodedData.substring(0, 32), 'hex');
    let decipher = crypto.createDecipheriv(algorithm, key, decodedIV);
    let decrypted = decipher.update(decodedData.substring(32), 'hex', 'utf8') + decipher.final('utf8');
    return decrypted;
}

In the encrypt function, I am concatenating the IV and text initially, then only updating the cipher.

On further research I came up with the following function to do the same.

//Concatenating iv after cipher.update
function encrypt(text) {
    let cipher = crypto.createCipheriv(algorithm, key, iv);
    let encrypted = cipher.update(Buffer.from(text));
    encrypted = Buffer.concat([Buffer.from(iv), encrypted, cipher.final()]);
    return encrypted.toString('base64');
}

In the encrypt function, I am concatenating the IV and text at last, only after updating the cipher with text.

Output of both encrypt functions can be decrypted using the same decrypt function. Is this expected?

[bnoordhuis]

See https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher_Feedback_(CFB) - aes-128-cfb is a self-synchronizing cipher.

If you want that a cipher that also preserves message integrity, turn to something like aes-256-gcm. Consult https://en.wikipedia.org/wiki/Authenticated_encryption for more info.

[PoojaDurgad]

ping- @jithinsk

[gireeshpunathil]

answered, closing. feel free to re-open if it is outstanding