aes_xctr(9)

💖 aes_xctr(9) 💖

okay bestie, so this is a page from the Kernel API Manual and it's literally all about aes_xctr — AES-XCTR en/decryption ✨ buckle up, it's giving cryptography but make it cute.

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🌸 NAME 🌸

aes_xctr — AES-XCTR en/decryption 🎀

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🦋 SYNOPSIS 🦋

void aes_xctr (u8 *dst , const u8 *src , size_t len , u64 *ctr , const
u8 iv[static AES_BLOCK_SIZE] , aes_encrypt_arg key );

like, that's the whole signature, no cap 💅

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🍓 ARGUMENTS 🍓

• dst — the destination buffer, bestie. it can be in-place or out-of-place, both are fine. for any other overlaps tho? the behavior is unspecified 😭 so like… don't.
• src — the source data, the actual bytes we're working with 🌈
• len — number of bytes to en/decrypt 🧚
• ctr — the block counter, and it's in host endianness (iykyk). for the first call, set it to:

1

and heads up — it gets incremented by ceil(len / AES_BLOCK_SIZE) 📈

• iv — the initialization vector 🎀
• key — the key, but not just any key — it's already prepared using aes_preparekey or aes_prepareenckey 👑

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👑 DESCRIPTION 👑

so this implements AES in XOR Counter mode, as specified in the paper "Length-preserving encryption with HCTR2" over at https://eprint.iacr.org/2021/1441.pdf 💖

lowkey important: this exists only for use by the implementation of modes built on top of XCTR. callers are expected to know how to use XCTR mode appropriately — including choosing (key, IV) pairs appropriately to avoid keystream reuse. like, that part is not optional, fr fr 🙈

it also supports incremental en/decryption ✨ the length of each non-final chunk must be a multiple of AES_BLOCK_SIZE, and the updated ctr must be passed in each time. no skipping, bestie 💅

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🔥 CONTEXT 🔥

Any context. literally any. slay 🫶

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⭐ SEE ALSO ⭐

• Kernel file ./include/crypto/aes-ctr.h
• aes_ctr(9) 🦋

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and that's the whole page, bestie — brought to you by the fine folks over at ./include/crypto, dated October 2026. periodt 💜✨🎀