CMAC_CTX(3)

CMAC_CTX(3) | OpenSSL | CMAC_CTX(3)

# NAME

CMAC_CTX, CMAC_CTX_new, CMAC_CTX_cleanup, CMAC_CTX_free, CMAC_CTX_get0_cipher_ctx, CMAC_CTX_copy, CMAC_Init, CMAC_Update, CMAC_Final, CMAC_resume - create cipher-based message authentication codes

# SYNOPSIS

     #include <openssl/cmac.h>

The following functions have been deprecated since OpenSSL 3.0, and can be disabled entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7).

     typedef struct CMAC_CTX_st CMAC_CTX;
     CMAC_CTX *CMAC_CTX_new(void);
     void CMAC_CTX_cleanup(CMAC_CTX *ctx);
     void CMAC_CTX_free(CMAC_CTX *ctx);
     EVP_CIPHER_CTX *CMAC_CTX_get0_cipher_ctx(CMAC_CTX *ctx);
     int CMAC_CTX_copy(CMAC_CTX *out, const CMAC_CTX *in);
     int CMAC_Init(CMAC_CTX *ctx, const void *key, size_t keylen,
                   const EVP_CIPHER *cipher, ENGINE *impl);
     int CMAC_Update(CMAC_CTX *ctx, const void *data, size_t dlen);
     int CMAC_Final(CMAC_CTX *ctx, unsigned char *out, size_t *poutlen);
     int CMAC_resume(CMAC_CTX *ctx);

# DESCRIPTION

The low-level MAC functions documented on this page are deprecated. Applications should use the new EVP_MAC(3) interface. Specifically, utilize the following functions for MAC operations:

EVP_MAC_CTX_new(3) to create a new MAC context.
EVP_MAC_CTX_free(3) to free the MAC context.
EVP_MAC_init(3) to initialize the MAC context.
EVP_MAC_update(3) to update the MAC with data.
EVP_MAC_final(3) to finalize the MAC and retrieve the output.

Alternatively, for a single-step MAC computation, use the EVP_Q_mac(3) function.

The CMAC_CTX type is a structure used for the provision of CMAC (Cipher-based Message Authentication Code) operations.

CMAC_CTX_new() creates a new CMAC_CTX structure and returns a pointer to it.

CMAC_CTX_cleanup() resets the CMAC_CTX structure, clearing any internal data but not freeing the structure itself.

CMAC_CTX_free() frees the CMAC_CTX structure and any associated resources. If the argument is NULL, no action is taken.

CMAC_CTX_get0_cipher_ctx() returns a pointer to the internal EVP_CIPHER_CTX structure within the CMAC_CTX.

CMAC_CTX_copy() copies the state from one CMAC_CTX structure to another.

CMAC_Init() initializes the CMAC_CTX structure for a new CMAC calculation with the specified key, key length, and cipher type. Optionally, an ENGINE can be provided.

CMAC_Update() processes data to be included in the CMAC calculation. This function can be called multiple times to update the context with additional data.

CMAC_Final() finalizes the CMAC calculation and retrieves the resulting MAC value. The output is stored in the provided buffer, and the length is stored in the variable pointed to by poutlen. To determine the required buffer size, call with out set to NULL, which stores only the length in poutlen. Allocate a buffer of this size and call CMAC_Final() again with the allocated buffer to retrieve the MAC.

CMAC_resume() resumes a previously finalized CMAC calculation, allowing additional data to be processed and a new MAC to be generated.

# RETURN VALUES

CMAC_CTX_new() returns a pointer to a new CMAC_CTX structure or NULL if an error occurs.

CMAC_CTX_get0_cipher_ctx() returns a pointer to the internal EVP_CIPHER_CTX structure, or NULL if an error occurs.

CMAC_CTX_copy(), CMAC_Init(), CMAC_Update(), CMAC_Final() and CMAC_resume() return 1 for success or 0 if an error occurs.

# HISTORY

All functions described here were deprecated in OpenSSL 3.0. For replacements, see EVP_MAC_CTX_new(3), EVP_MAC_CTX_free(3), EVP_MAC_init(3), EVP_MAC_update(3), and EVP_MAC_final(3).

# COPYRIGHT

Copyright 2024 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

2026-06-09 | 3.5.7