hmac_sha256(9)

💅 hmac_sha256 — the kernel API manual, bestie edition 🎀

Okay so real talk: this is hmac_sha256(9), and it lives in the Kernel API Manual. She's a one-shot girlie — you give her a key you already prepped and a blob of data, and she hands you back the HMAC-SHA256. No drama, no state, no nothing. ✨

---

🌸 NAME 🌸

hmac_sha256 — compute HMAC-SHA256 in one shot, using a prepared key

---

🦋 SYNOPSIS 🦋

void hmac_sha256 (const struct hmac_sha256_key *key , const u8 *data ,
size_t data_len , u8 out[static SHA256_DIGEST_SIZE] );

---

💖 ARGUMENTS 💖

• key — the prepared HMAC key. Like, prepared prepared. It's a const struct hmac_sha256_key * and it must already be ready to go — no raw-key chaos here.
• data — the message data. Your actual payload, an array of u8, hearts to it.
• data_len — the data length in bytes, size_t style, because the kernel is nothing if not precise.
• out — (output) the resulting HMAC-SHA256 value. It's u8 out[static SHA256_DIGEST_SIZE] — the digest lands here and it's iconic. 👑

---

🧚 DESCRIPTION 🧚

So here's the vibe check: if you're only using the key once, consider using hmac_sha256_usingrawkey instead. That's it, that's the whole note — she's telling you there's a shorter path if your key isn't sticking around for round two. 💅

---

🔥 CONTEXT 🔥

Any context. Literally any. No locks, no sleep rules, no "only from process context" gatekeeping. Slay. 🫶

---

🌈 SEE ALSO 🌈

Whole fam, all of them, no cap:

• Kernel file ./include/crypto/sha2.h
• struct sha224_ctx(9), sha224_init(9), sha224_update(9), sha224_final(9), sha224(9)
• struct hmac_sha224_key(9), struct hmac_sha224_ctx(9), hmac_sha224_preparekey(9), hmac_sha224_init(9), hmac_sha224_init_usingrawkey(9), hmac_sha224_update(9), hmac_sha224_final(9), hmac_sha224(9), hmac_sha224_usingrawkey(9)
• struct sha256_ctx(9), sha256_init(9), sha256_update(9), sha256_final(9), sha256(9), sha256_finup_2x(9), sha256_finup_2x_is_optimized(9)
• struct hmac_sha256_key(9), struct hmac_sha256_ctx(9), hmac_sha256_preparekey(9), hmac_sha256_init(9), hmac_sha256_init_usingrawkey(9), hmac_sha256_update(9), hmac_sha256_final(9), hmac_sha256_usingrawkey(9)
• struct sha384_ctx(9), sha384_init(9), sha384_update(9), sha384_final(9), sha384(9)
• struct hmac_sha384_key(9), struct hmac_sha384_ctx(9), hmac_sha384_preparekey(9), hmac_sha384_init(9), hmac_sha384_init_usingrawkey(9), hmac_sha384_update(9), hmac_sha384_final(9), hmac_sha384(9), hmac_sha384_usingrawkey(9)
• struct sha512_ctx(9), sha512_init(9), sha512_update(9), sha512_final(9), sha512(9)
• struct hmac_sha512_key(9), struct hmac_sha512_ctx(9), hmac_sha512_preparekey(9), hmac_sha512_init(9), hmac_sha512_init_usingrawkey(9), hmac_sha512_update(9), hmac_sha512_final(9), hmac_sha512(9), hmac_sha512_usingrawkey(9)

---

That's the whole page, bestie — no crumbs left behind. 🍓

Signed off from the ./include/crypto directory, dated October 2026 — hmac_sha256(9) ate and left absolutely zero notes. 💜