# Symmetric Cryptography Symmetric ciphers are algorithms that use the same key both to encrypt and decrypt data. The goal is to use short secret keys to securely and efficiently send long messages. We can split symmetric-key ciphers into two types, block ciphers and stream ciphers. Block ciphers break up a plaintext into fixed-length blocks, and send each block through an encryption function together with a secret key. Stream ciphers meanwhile encrypt one byte of plaintext at a time, by XORing a pseudo-random keystream with the data. Block ciphers only specify how to encrypt and decrypt individual blocks, and a mode of operation must be used to apply the cipher to longer messages. --- # 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://www.ctfrecipes.com/cryptography/symmetric-cryptography.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.