KCAPI_KPP_DH_SETPARA(3)

💖 KCAPI_KPP_DH_SETPARA 💖

okay bestie, welcome to kcapi_kpp_dh_setparam_pkcs3 — yes the page title is KCAPI_KPP_DH_SETPARA and the function is kcapi_kpp_dh_setparam_pkcs3, that's just how libkcapi names things, we move 💅 — it lives in section 3 of the manual and it's all about handing the kernel your Diffie-Hellman PG parameters. sit down, hydrate, let's go 🌸

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✨ NAME ✨

kcapi_kpp_dh_setparam_pkcs3 — set the PG parameters using PKCS3 format 🎀

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✨ SYNOPSIS ✨

int kcapi_kpp_dh_setparam_pkcs3(struct kcapi_handle * handle,
                                const uint8_t * pkcs3,
                                uint32_t pkcs3len);

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✨ ARGUMENTS ✨

• handle — [in] your cipher handle, the little main character 🫶
• pkcs3 — [in] the parameter buffer, and it has to be in DER format
• pkcs3len — [in] the length of the key buffer

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✨ DESCRIPTION ✨

so with this function, the caller sets the PG parameters for all the cipher operations that come after it. literally setting the vibe for everything downstream ✨

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

SEQUENCE { prime INTEGER ({ dh_get_p }), base INTEGER ({ dh_get_g }) }

The following command generates such a parameter set where the output…

🌈 FILE CONTENT IS HAS THE CORRECT DER STRUCTURE 🌈

openssl dhparam -outform DER -out dhparam.der 2048

(and yes bestie, that heading is verbatim, we don't edit the ancestors' grammar, we respect them 🙈)

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ngl, this next part matters: this function defines that the subsequent key generation and shared secret operation performs an FFC Diffie-Hellman operation. so like, you're not just passing bytes, you're committing to FFC DH, no take-backs 🔥

After the caller provided the key, the caller may destroy the parameter as it is now maintained by the kernel. the kernel has custody now, you can let it go 💜

and as for what you get back — return upon success the value of the maximum size for the KPP operation is returned (e.g. the prime size); a negative errno-style error code if an error occurred. so success = a number, sadness = a negative errno 💀

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✨ AUTHOR ✨

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

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✨ COPYRIGHT ✨

this one's the official libkcapi page, so go be normal about licensing and check the actual copyright terms, bestie 🎀

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okay that's the whole page!! sending you off with the official energy: libkcapi Manual 1.5.0, July 2025 🦋 go forth and Diffie-Hellman responsibly, ily, periodt 💖✨