Index out of range: index should be less than 36: 36 about encrypt

[leocavalcante]

When not padded, inputs should be multiples of the block size. Can you share your input or an input that reproduces the error?

[Jethro87]

Hi @leocavalcante 👋

Sure thing. I'm trying to encrypt a String of 'String'.

var encrypted = crypto.encrypt('String');
print(encrypted.base16);

I get this error: flutter: Another exception was thrown: RangeError (index): Index out of range: index should be less than 6: 6

On a higher level, what I'm trying to do is be able to encrypt/decrypt in my Flutter app (using encrypt) and my web app (using aesjs). Aesjs (using Aes.ctr), does not require padding as per their example below:

var key = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ];

// Convert text to bytes
var text = 'Text may be any length you wish, no padding is required.';
var textBytes = aesjs.utils.utf8.toBytes(text);

// The counter is optional, and if omitted will begin at 1
var aesCtr = new aesjs.ModeOfOperation.ctr(key, new aesjs.Counter(5));
var encryptedBytes = aesCtr.encrypt(textBytes);

// To print or store the binary data, you may convert it to hex
var encryptedHex = aesjs.utils.hex.fromBytes(encryptedBytes);
console.log(encryptedHex);
// "a338eda3874ed884b6199150d36f49988c90f5c47fe7792b0cf8c7f77eeffd87
//  ea145b73e82aefcf2076f881c88879e4e25b1d7b24ba2788"

// When ready to decrypt the hex string, convert it back to bytes
var encryptedBytes = aesjs.utils.hex.toBytes(encryptedHex);

// The counter mode of operation maintains internal state, so to
// decrypt a new instance must be instantiated.
var aesCtr = new aesjs.ModeOfOperation.ctr(key, new aesjs.Counter(5));
var decryptedBytes = aesCtr.decrypt(encryptedBytes);

// Convert our bytes back into text
var decryptedText = aesjs.utils.utf8.fromBytes(decryptedBytes);
console.log(decryptedText);
// "Text may be any length you wish, no padding is required."

If I encrypt the string 'String' in aesjs and print the base16 result, I get this:

0d957ea17dad

If I encrypt the string 'String' in encrypt without setting padding: null, I get this:

0d957ea17dad88c50c817dac320c1bbc

But if I set padding: null, I get this error: flutter: Another exception was thrown: RangeError (index): Index out of range: index should be less than 6: 6

Would you mind elaborating on your point, with respect to what I'm trying to do as per above? I'm quite new to encryption. Thanks for your time.

[Jethro87]

I managed to figure this out. Ended up using CBC instead of CTR, with padding. Closing this issue.