---
name: "kcapi_cipher_dec_sm4_cbc"
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_cipher_dec_sm4_cbc"
---

# kcapi\_cipher\_dec\_sm4\_cbc(3)

Convenience function for SM4 CBC decryption

## NAME

kcapi\_cipher\_dec\_sm4\_cbc - Convenience function for SM4 CBC decryption

## SYNOPSIS

**ssize\_t kcapi\_cipher\_dec\_sm4\_cbc(const uint8\_t \*** *key***, uint32\_t** *keylen***, const uint8\_t \*** *in***, size\_t** *inlen***, const uint8\_t \*** *iv***, uint8\_t \*** *out***, size\_t** *outlen***);**

## ARGUMENTS

*key*

\[in\] key buffer

*keylen*

\[in\] length of key buffer

*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

## DESCRIPTION

The convenience function performs an SM4 CBC decryption operation using the provided key, the given input buffer and the given IV. The output is stored in the out buffer.

Note, SM4 CBC requires an input data that is a multiple of 16 bytes. If you have data that is not guaranteed to be multiples of 16 bytes, either add zero bytes at the end of the buffer to pad it up to a multiple of 16 bytes. Otherwise, the CTR mode encryption operation may be usable.

The output buffer must be at least as large as the input buffer.

The IV must be exactly 16 bytes in size.

The SM4 key is fixed 16 bytes long.

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

## AUTHOR

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

Author.

## COPYRIGHT