CryptoJS example

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<script>

var CS_256_SHA_AES_CTR = 1;

// Note that CryptoJS uses MSB first for word arrays.
// converts J/S Array (not [] array) into
// CryptoJS WordArray.
function makeWA(input) {

    var l = input.byteLength;

    if (l !== input.length) {
        throw new Error("only 8 byte arrays are allowed!");
    }

    var data = [];
    var acc = 0;
    var j = 0;
    var i = 0;
    while (i<l) {

        var r = i % 4;
        acc = acc | (input[i] << 8*(3-r));
        i++;
        if (r === 3 || i === l) {
            data[j++] = acc;
            acc = 0;
        }
    }

    return new CryptoJS.lib.WordArray.init(data, l);
}

// this function takes in WordArray and returns
// back a Uint8Array
function unmakeWA(res) {
    var l = res.sigBytes;
    var data = new Uint8Array(l);
    for (var i=0,j=-1; i<l; i++) {
        var r = i%4;
        if (r === 0) { j++; }
        var word = res.words[j] >> ((3-r)*8);
        data[i] = word;
    }
    return data;
}

// I assume that srpKey is Uint8Array
// input is also a Uin8Array, containing IV followed by the data.
function decrypt(input, srpKey, cipherSuite) {
    if (cipherSuite != CS_256_SHA_AES_CTR) {
        throw new Error("Unsupported cipher suite : " + cipherSuite);
    }
    var aesKey = CryptoJS.SHA256(makeWA(srpKey));
    // so that we know the size of the elements,
    // let's convert this to 8-byte array if it's not
    if (input.byteLength !== input.length) {
        input = new Uint8Array(input.buffer);
    }
    // we know that AES always has 128 bit block size, so that's
    // how much we need for IV (128/8 = 16)
    var iv = makeWA(input.subarray(0, 16));
    input = input.subarray(16);

    // console.log("decrypting bytes:"+JSON.stringify(input));
    // console.log("decrypting words:"+JSON.stringify(makeWA(input).words));
    // console.log("decrypting "+makeWA(input).sigBytes+" bytes");

    return CryptoJS.AES.decrypt({ciphertext:makeWA(input)}, aesKey, { iv: iv, mode: CryptoJS.mode.CTR, padding: CryptoJS.pad.NoPadding} ).toString(CryptoJS.enc.Utf8);
}

// input is string
// output is Uint8Array
function encrypt(input, srpKey, cipherSuite) {
    if (cipherSuite != CS_256_SHA_AES_CTR) {
        throw new Error("Unsupported cipher suite : " + cipherSuite);
    }
    var aesKey = CryptoJS.SHA256(makeWA(srpKey));
    // aesKey = new CryptoJS.lib.WordArray.init([0x2b7e1516, 0x28aed2a6, 0xabf71588, 0x09cf4f3c ]);
    // generate IV (again, 16 bytes)
    var iv = CryptoJS.lib.WordArray.random(16);
    // var iv = new CryptoJS.lib.WordArray.init([0,0,0,0]);
    // var iv = new CryptoJS.lib.WordArray.init([0xf0f1f2f3, 0xf4f5f6f7, 0xf8f9fafb, 0xfcfdfeff]);
    // input = new CryptoJS.lib.WordArray.init([0x6bc1bee2, 0x2e409f96, 0xe93d7e11, 0x7393172a ])
    var res = CryptoJS.AES.encrypt(input, aesKey, { iv : iv, mode : CryptoJS.mode.CTR, padding: CryptoJS.pad.NoPadding} ).ciphertext;
    // console.log("test decrypt:"+CryptoJS.AES.decrypt({ciphertext:res}, aesKey, {iv:iv, mode : CryptoJS.mode.CTR, padding: CryptoJS.pad.NoPadding}).toString(CryptoJS.enc.Utf8));
    // convert CryptoJS word array to J/S, but we also need to include IV.
    // IV is 4 words.
    // console.log("encrypted words:"+JSON.stringify(res.words));
    res.words.unshift(iv.words[0], iv.words[1], iv.words[2], iv.words[3]);
    res.sigBytes += 16;
    // res = new Uint32Array(res.words);
    // return new Uint8Array(res.buffer);
    // console.log("returning "+data.length+" bytes (cipher text is "+(data.length-16)+")");
    // return new Uint8Array(data);
    return unmakeWA(res);
}

// test

var srpKey = new Uint8Array([1,2,3,4]);
var testData = "brown fox jumped over things";
console.log("plaintext:"+testData);
var coded = encrypt(testData, srpKey, CS_256_SHA_AES_CTR);
console.log("encoded: "+CryptoJS.enc.Base64.stringify(makeWA(coded)));
var decoded = decrypt(coded, srpKey, CS_256_SHA_AES_CTR);
console.log("decoded  :"+decoded);

function base64test(val) {
    console.log(decrypt(unmakeWA(CryptoJS.enc.Base64.parse(val)), srpKey, CS_256_SHA_AES_CTR));
}

</script>

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