KCAPI_AKCIPHER_SETKE(3)

💖 NAME 💖

kcapi_akcipher_setkey — bestie, this is the one that sets the private key for the cipher handle 🔑

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✨ SYNOPSIS ✨

int kcapi_akcipher_setkey(struct kcapi_handle * handle,
                          const uint8_t * key, uint32_t keylen);

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🎀 ARGUMENTS 🎀

• handle — [in] the cipher handle, aka the little guy you're doing all this for 🫶
• key — [in] the key buffer, and it's gotta be in DER format or it's not the vibe
• keylen — [in] how long that key buffer is, in bytes

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🌸 DESCRIPTION 🌸

Okay so basically: you call this and the caller sets the key for all the cipher operations that come next. That's it, that's the whole job. ✨

The key must be in DER format, and it has to look exactly like this:

SEQUENCE { version INTEGER, n INTEGER ({ rsa_get_n }), e INTEGER ({ rsa_get_e }), d INTEGER ({ rsa_get_d }), prime1 INTEGER, prime2 INTEGER, exponent1 INTEGER, exponent2 INTEGER, coefficient INTEGER }

Not me being dramatic but 💀 if it's not in this DER shape it's giving "nope".

Once the caller has handed the key over, the caller may securely destroy the key — because at that point it's being maintained by the kernel, so it's not your problem anymore. Lowkey iconic. 👑

As for what comes back: upon success, the return value is the maximum size for the asymmetric operation (like, say, the modulus size 🌈). And if something went wrong? You get a negative errno-style error code. No cap. 😭

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🦋 AUTHOR 🦋

Stephan Mueller <smueller@chronox.de> — Author. 🫶

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💅 COPYRIGHT 💅

libkcapi Manual 1.5.0 July 2025 — that's the version and the date, bestie, and that's the whole page, fr fr 🌸💖✨