Block Unpadding

Category: Utility · Node Type ID: padding-block-unpad

Removes cryptographic block padding (PKCS#7, ANSI X9.23, ISO/IEC 9797-1 Method 2/3, None)

Overview

Validates and strips cryptographic block padding from a block-aligned byte array according to the selected Padding Standard (PKCS7, ISO7816, ISO97971M3, ANSIX923, or None) and Block Size (Bytes) (8, 16, or 32).

If the input byte length is not a positive multiple of the block size or if the trailing bytes violate the structure of the selected padding rule, execution halts with an error. Note that Zero and NIST80038B padding are not reversible without external length knowledge and are therefore excluded from automatic unpadding.

When to Use

Stripping and verifying block padding after decrypting with a cipher node configured with Padding = None.
Testing padding-oracle / malformed-padding error handling in custom workflows.

Parameter Configuration

Parameter (ID)	Type & Default	Visibility Condition	Description & Options
Padding Standard `paddingType`	`select` Default: `None`	Always visible	Selects the reversible padding standard to verify and remove (`PKCS7`, `ISO7816`, `ISO97971M3`, `ANSIX923`, or `None`). See Padding Schemes. `None`: None `ISO7816`: ISO/IEC 9797-1 Method 2 (ISO/IEC 7816-4) `ISO97971M3`: ISO/IEC 9797-1 Method 3 `PKCS7`: PKCS#7 (RFC 5652) `ANSIX923`: ANSI X9.23
Block Size (Bytes) `blockSize`	`select` Default: `16`	Always visible	Block size in bytes (`8`, `16`, or `32`) that the input buffer must be aligned to. `8`: 8 Bytes (64 bits - DES/3DES) `16`: 16 Bytes (128 bits - AES/SEED/ARIA/Camellia/SM4) `32`: 32 Bytes (256 bits)
Unify Errors `errorUnify`	`boolean` Default: `false` Supports Variable Reference (`$var`: `bool`)	Always visible	Replaces built-in errors with a custom error code/message when enabled.
Unified Error Code `errorUnifyCode`	`text` Default: `""` (empty) Supports Variable Reference (`$var`: `string`)	When `errorUnify` is `true`	Custom error code when Unify Errors is enabled.
Unified Error Message `errorUnifyMessage`	`text` Default: `""` (empty) Supports Variable Reference (`$var`: `string`)	When `errorUnify` is `true`	Custom error message when Unify Errors is enabled.

Port I/O Specification

See Ports & Connections for general wiring rules, data type colors, and dynamic port creation.

Input Ports

Port Nature: Fixed Input Ports (1 total).

Port Name	Port ID	Data Type	Required	Visibility Condition	Description
`Padded Data`	`data`	`Bytes`	Required	Always visible	Unpadded original byte array (`Uint8Array`).

Output Ports

Port Nature: Fixed Output Ports (1 total).

Port Name	Port ID	Data Type	Visibility Condition	Description
`Data`	`result`	`Bytes`	Always visible

Error Cases

When any of the following conditions occurs at runtime, this node transitions to an ERROR state and downstream nodes connected to its outputs do not execute. Enabling Unify Errors (errorUnify) replaces all error codes below with your configured unified error code and message.

Error Code	Default Engine Message	Trigger Condition
`INVALID_PADDING`	Invalid padding	Raised when the decrypted or input block's trailing bytes violate the structure of the selected padding standard.

Examples

Unpadding Decrypted Block Data

Strip PKCS#7 padding from a 16-byte decrypted block.

Connect the output of a raw decrypt node (Padding = None) to Padded Data on Block Unpadder.
Set Padding Standard to PKCS#7 and Block Size to 16 to recover the original unpadded bytes on Unpadded Data.