Appends PKCS#7 padding to data.
If the input is already aligned, a full block of padding is added.
@eryx/crypto/hazmat/pkcs7 Module
PKCS#7 padding helpers for block ciphers.
This library is intended to pair with the raw block-cipher APIs in
@eryx/crypto/hazmat/*. It pads arbitrary-length data up to a block
boundary and validates/removes PKCS#7 padding explicitly.
local aes = require("@eryx/crypto/hazmat/aes")
local pkcs7 = require("@eryx/crypto/hazmat/pkcs7")
local key = buffer.create(16)
local iv = buffer.create(16)
local padded = pkcs7.pad(buffer.fromstring("hello"), 16)
local encrypt = aes.new(key, "cbc", "encrypt", iv)
local ct = buffer.concat({ encrypt:update(padded), encrypt:final() })
local decrypt = aes.new(key, "cbc", "decrypt", iv)
local pt = pkcs7.unpad(buffer.concat({ decrypt:update(ct), decrypt:final() }), 16)
Summary
Functions
API Reference
Functions
pkcs7.pad
pkcs7.pad(data: buffer, blockSize: number) → buffer
Parameters
data: buffer
Raw input bytes.
blockSize: number
Block size in bytes, typically 8 or 16.
Returns
buffer
New buffer containing the padded data.
pkcs7.unpad
Validates and removes PKCS#7 padding from data.
The input length must be non-zero and a multiple of blockSize.
Padding validation runs in constant time with respect to the buffer
contents: every candidate padding byte is examined regardless of the
encoded length, and a single generic error is raised on any failure, so an
attacker cannot learn which byte was wrong from timing or error text. Note
that this does not remove the padding oracle entirely — a caller can still
observe success versus failure, and the returned length reveals padLen.
To defend against padding-oracle attacks, pair this with authenticated
encryption (see @eryx/crypto/secretbox) or verify a MAC before unpadding.
pkcs7.unpad(data: buffer, blockSize: number) → buffer
Parameters
data: buffer
Padded input bytes.
blockSize: number
Block size in bytes, typically 8 or 16.
Returns
buffer
New buffer containing the unpadded data.