awaforge

ctr

Apache-2.0Release 1L3

AES-CTR (SP 800-38A §6.5) — stream mode, no padding, encrypt/decrypt involution.

Module ctr | Source packages/front/fw/src/crypto/mode/ctr.js | Deps bitArray, aes | Worker-safe yes

CTR = stream cipher derived from a block cipher. Unauthenticated: use GCM for AEAD. Nonce reuse is catastrophic: 2 messages under an identical (key, IV) → keystream recovery.

Resolve

const ctr = runtime.resolve('ctr');
// Returns: { encrypt }

API

Method Signature Returns
encrypt(prf, dataBa, ivBa, prefix) ({encrypt}, bitArray, bitArray, string) => bitArray | false data XOR keystream (involution → encrypt = decrypt)

Examples

const { aes, ctr, bitArray } = fw.runtime.resolveAll(['aes', 'ctr', 'bitArray']);

const cipher = aes.fn(keyWords);
const ivBa  = bitArray.ui8_to_ba(nonce16);

const ct = ctr.encrypt(cipher, ptBa, ivBa, '');
const pt = ctr.encrypt(cipher, ct, ivBa, '');   // involution

Worker Usage

const worker = fw.createWorker(
    function ({ libs, args }) {
        const cipher = libs.aes.fn(args[0]);
        self.postMessage(libs.ctr.encrypt(cipher, args[1], args[2], ''));
    },
    { dependencies: ['aes', 'ctr'], args: [keyWords, dataBa, ivBa] }
);

Notes

  • Stream cipher: encrypt(encrypt(pt)) = pt (involution).
  • No padding: arbitrary-length payload (incl. non-byte/non-block-aligned via bitArray.clamp).
  • Nonce uniqueness: the caller's responsibility. For AEAD with a nonce-tracker, use GCM.

See also