# Authentication key (Ki) The Ki is a secret key that is used to authenticate the subscriber on the network. It is stored securely in the SIM card's memory and is never transmitted over the network. When the subscriber tries to access the network, the SIM card uses the Ki to generate a response that is sent to the network for authentication. In addition to these key components, SIM cards may also include other features such as security mechanisms to protect against unauthorized access, storage for contacts and text messages, and even a small amount of memory for storing music or other media. --- # 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://sim-cards.learn-telecom.com/gsm-identifiers/authentication-key-ki.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.