---
name: "kcapi_aead_decrypt"
section: "3"
platform: "linux"
package: "libkcapi-dev"
version: "1.4.0-1+b2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/kcapi_aead_decrypt"
---

# kcapi\_aead\_decrypt(3)

synchronously decrypt AEAD data (one shot)

## NAME

kcapi\_aead\_decrypt - synchronously decrypt AEAD data (one shot)

## SYNOPSIS

**ssize\_t kcapi\_aead\_decrypt(struct kcapi\_handle \*** *handle***, const uint8\_t \*** *in***, size\_t** *inlen***, const uint8\_t \*** *iv***, uint8\_t \*** *out***, size\_t** *outlen***, int** *access***);**

## ARGUMENTS

*handle*

\[in\] cipher handle

*in*

\[in\] ciphertext data buffer

*inlen*

\[in\] length of in buffer

*iv*

\[in\] IV to be used for cipher operation

*out*

\[out\] plaintext data buffer

*outlen*

\[in\] length of out buffer

*access*

\[in\] kernel access type (KCAPI\_ACCESS\_HEURISTIC - use internal heuristic for fastest kernel access; KCAPI\_ACCESS\_VMSPLICE use vmsplice access; KCAPI\_ACCESS\_SENDMSG sendmsg access)

## DESCRIPTION

The AEAD cipher operation requires the furnishing of the associated authentication data. In case such data is not required, it can be set to NULL and length value must be set to zero.

It is perfectly legal to use the same buffer as the plaintext and ciphertext pointers. That would mean that after the encryption operation, the ciphertext is overwritten with the plaintext.

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 data to the kernel.

The IV buffer must be exactly **kcapi\_cipher\_ivsize** bytes in size.

To catch authentication errors (i.e. integrity violations) during the decryption operation, the return value of this call should be checked. If this function returns -EBADMSG, an authentication error was detected.

## IMPORTANT NOTE

The kernel will only process sysconf(\_SC\_PAGESIZE) \* ALG\_MAX\_PAGES at one time. Longer input data cannot be handled by the kernel.

*return* number of bytes decrypted upon success; a negative errno-style error code if an error occurred

## AUTHOR

**Stephan Mueller** \<smueller@chronox.de\>

Author.

## COPYRIGHT