How to convert padbytes function to coldfusion - node.js

Question

I have the following code in node and I am trying to convert to ColdFusion:
// a correct implementation of PKCS7. The rijndael js has a PKCS7 padding already implemented
// however, it incorrectly pads expecting the phrase to be multiples of 32 bytes when it should pad based on multiples
// 16 bytes. Also, every javascript implementation of PKCS7 assumes utf-8 char encoding. C# however is unicode or utf-16.
// This means that chars need to be treated in our code as 2 byte chars and not 1 byte chars.
function padBytes(string){
const strArray = [...new Buffer(string, 'ucs2')];
const need = 16 - ((strArray.length) % 16);
for(let i = 0; i < need; i++) {
strArray.push(need);
}
return Buffer.from(strArray);
}
I'm trying to understand exactly what this function is doing to convert it. As I think I understand it, it's converting the string to UTF-16 (UCS2) and then adding padding to each character. However, I don't understand why the need variable is the value it is, nor how exactly to achieve that in CF.
I also don't understand why it's only pushing the same value into the array over and over again. For starters, in my example script the string is 2018-06-14T15:44:10Z testaccount. The string array length is 64. I'm not sure how to achieve even that in CF.
I've tried character encoding, converting to binary and stuff to UTF-16 and just don't understand well enough the js function to replicate it in ColdFusion. I feel I'm missing something with the encoding.
EDIT:
The selected answer solves this problem, but because I was eventually trying to use the input data for encryption, the easier method was to not use this function at all but do the following:
<cfset stringToEncrypt = charsetDecode(input,"utf-16le") />
<cfset variables.result = EncryptBinary(stringToEncrypt, theKey, theAlgorithm, theIV) />

Answer 1

Update:
We followed up in chat and turns out the value is ultimately used with encrypt(). Since encrypt() already handles padding (automatically), no need for the custom padBytes() function. However, it did require switching to the less commonly used encryptBinary() function to maintain the UTF-16 encoding. The regular encrypt() function only handles UTF-8, which produces totally different results.
Trycf.com Example:
// Result with sample key/iv: P22lWwtD8pDrNdQGRb2T/w==
result = encrypt("abc", theKey, theAlgorithm, theEncoding, theIV);
// Result Result with sample key/iv: LJCROj8trkXVq1Q8SQNrbA==
input = charsetDecode("abc", "utf-16le");
result= binaryEncode(encryptBinary(input, theKey, theAlgorithm, theIV), "base64);
it's converting the string to utf-16
(ucs2) and then adding padding to each character.
... I feel I'm missing something with the encoding.
Yes, the first part seems to be decoding the string as UTF-16 (or UCS2 which are slightly different). As to what you're missing, you're not the only one. I couldn't get it to work either until I found this comment which explained "UTF-16" prepends a BOM. To omit the BOM, use either "UTF-16BE" or "UTF-16LE" depending on the endianess needed.
why it's only pushing the same value into the array over and over again.
Because that's the definition of PCKS7 padding. Instead of padding with something like nulls or zeroes, it calculates how many bytes padding are needed. Then uses that number as the padding value. For example, say a string needs an extra three bytes padding. PCKS7 appends the value 3 - three times: "string" + "3" + "3" + "3".
The rest of the code is similar in CF. Unfortunately, the results of charsetDecode() aren't mutable. You must build a separate array to hold the padding, then combine the two.
Note, this example combines the arrays using CF2016 specific syntax, but it could also be done with a simple loop instead
Function:
function padBytes(string text){
var combined = [];
var padding = [];
// decode as utf-16
var decoded = charsetDecode(arguments.text,"utf-16le");
// how many padding bytes are needed?
var need = 16 - (arrayLen(decoded) % 16);
// fill array with any padding bytes
for(var i = 0; i < need; i++) {
padding.append(need);
}
// concatenate the two arrays
// CF2016+ specific syntax. For earlier versions, use a loop
combined = combined.append(decoded, true);
combined = combined.append(padding, true);
return combined;
}
Usage:
result = padBytes("2018-06-14T15:44:10Z testaccount");
writeDump(binaryEncode( javacast("byte[]", result), "base64"));