awaforge

pad

Apache-2.0Release 1L3

PKCS#7 padding (RFC 5652 §6.3) — pad/strip for block modes without built-in padding (CBC, ECB).

Module pad | Source packages/front/fw/src/crypto/utils/pad.js | Deps none | Worker-safe yes

Resolve

const pad = runtime.resolve('pad');
// Returns: { pad, strip, fast: { pad, strip } }

API

Method Signature Returns
pad(data) (Uint8Array | number[]) => Uint8Array | false PKCS#7 padded, false if input invalid
strip(data) (Uint8Array | number[]) => Uint8Array | false Unpad, false if invalid (length, padding bytes)
fast.pad(data) (Uint8Array) => Uint8Array | false Like pad but without element-by-element validation
fast.strip(data) (Uint8Array) => Uint8Array | false Like strip, trusted Uint8Array input only

Note: block size is fixed at 16 (AES). No blockSize parameter. pad never throws — returns false + console.warn on invalid input.

Examples

const { pad } = fw.runtime.resolveAll(['pad']);

const padded = pad.pad(new Uint8Array([1, 2, 3]));
// Uint8Array [1, 2, 3, 13, 13, ..., 13]  (13 bytes of PKCS#7 padding)
const back   = pad.strip(padded);   // Uint8Array [1, 2, 3]

// Fast variant (trusted Uint8Array input, no element-level validation)
const padded2 = pad.fast.pad(new Uint8Array([1, 2, 3]));
const back2   = pad.fast.strip(padded2);   // Uint8Array [1, 2, 3]

Worker Usage

const worker = fw.createWorker(
    function ({ libs, args }) { self.postMessage(libs.pad.pad(args[0])); },
    { dependencies: ['pad'], args: [new Uint8Array([1,2,3])] }
);

Notes

  • Idempotence: if the input already ends with a valid PKCS#7 block, pad appends a full extra 16-byte block — intentional behaviour per RFC 5652 §6.3.
  • strip constant-time: verifies the padLen padding bytes via XOR-accumulation (branchless mask (i >= BLOCK - padLen) ? 1 : 0) — no early-exit on an invalid byte.
  • Padding oracle: even with CT strip, authenticate the ciphertext before decryption (encrypt-then-MAC or use AEAD). Returning false remains observable if total timing is measured.
  • fast.pad/strip: bypasses the _isByteArray validation — use only with Uint8Array inputs of controlled origin.

See also