# Pointer Authentication ## Overview Pointer Authentication is a hardware feature available for Arm devices to protect against ROP attacks. A **Pointer Authentication Code** (PAC) is generated from the value of a given pointer, and must be used to verify pointers before using them. This protection requires **hardware support**, as the assembly instructions (such as [`paciasp`](https://developer.arm.com/documentation/ddi0602/2024-03/Base-Instructions/PACIA--PACIA1716--PACIASP--PACIAZ--PACIZA--Pointer-Authentication-Code-for-Instruction-address--using-key-A-) and [`retaa`](https://developer.arm.com/documentation/ddi0602/2025-12/Base-Instructions/RETAA--RETAB--Return-from-subroutine--with-pointer-authentication-)) that are required for this must exist on the processor, and **compiler support**. PAC has two keys, called Key A and Key B. The instruction `paciasp` will sign the Link Register (`lr`) using Key A and the SP register, and is often used at function entry (to store the return pointer). `pacibsp` will do the same, but with Key B. At function exit, when LR is popped off the stack, we use the `retaa` instruction instead. This instruction authenticates the address in LR using Key A and SP and branches to the authenticated address. `retab` is used for Key B instead. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://ir0nstone.gitbook.io/notes/binexp/stack/pointer-authentication.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.