KCAPI_AKCIPHER_DECRY(3)

✨ KCAPI_AKCIPHER_DECRY(3) ✨

okay bestie, welcome to the libkcapi manual, section 3 🎀 this one's about kcapi_akcipher_decrypt — the glow-up machine that turns your ciphertext back into readable plaintext. no cap. 💅

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🌸 NAME 🌸

kcapi_akcipher_decrypt — decrypt data 🦋

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⭐ SYNOPSIS ⭐

ssize_t kcapi_akcipher_decrypt(struct kcapi_handle * handle,
                               const uint8_t * in, size_t inlen,
                               uint8_t * out, size_t outlen,
                               int access);

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💖 ARGUMENTS 💖

• handle — [in] your cipher handle. the main character of this whole operation 👑
• in — [in] the ciphertext data buffer. this is the mystery box you're opening 🙈
• inlen — [in] how long that in buffer is, in bytes.
• out — [out] the plaintext data buffer. this is where the reveal lands ✨
• outlen — [in] how long the out buffer is.
• access — [in] which kernel access type you want:
  • KCAPI_ACCESS_HEURISTIC — use the internal heuristic to figure out the fastest kernel access 🔥
  • KCAPI_ACCESS_VMSPLICE — use vmsplice access
  • KCAPI_ACCESS_SENDMSG — use sendmsg access

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🌈 DESCRIPTION 🌈

it is perfectly legal to use the same buffer for both the plaintext and ciphertext pointers. like, go off. what that means is: after the decryption operation finishes, the ciphertext gets overwritten with the plaintext. one buffer, two eras. 💀

now, the memory should be aligned at the page boundary using posix_memalign(sysconf(_SC_PAGESIZE)). if it is not aligned at the page boundary, the vmsplice call may not send all the data to the kernel. so like… align it, bestie, it's giving self-care 🧚

if the output size is insufficiently large, -EINVAL is returned. the output buffer must be at least as large as the modulus of the key being used. no shortcuts, that's the rule 😭

on success you get back the number of bytes returned by the decryption operation; if something went wrong you get a negative errno-style error code instead. slay when it works, weep when it doesn't 🫶

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💜 AUTHOR 💜

Stephan Mueller <smueller@chronox.de> Author.

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👑 COPYRIGHT 👑

that's the whole page, bestie — periodt. 💖

this was libkcapi Manual 1.5.0, dated July 2025, and yes the title up top says KCAPI_AKCIPHER_DECRY(3). go decrypt something iconic ✨🦋🌸