lc_aes_gcm.h

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/*
 * Copyright (C) 2022 - 2025, Stephan Mueller <smueller@chronox.de>
 *
 * License: see LICENSE file in root directory
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
 * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 */
 
#ifndef LC_AES_GCM_H
#define LC_AES_GCM_H
 
#include "lc_aead.h"
#include "lc_sym.h"
 
#ifdef __cplusplus
extern "C" {
#endif

struct lc_gcm_ctx {
        uint64_t len; // cipher data length processed so far
        uint64_t aad_len; // total add data length
        uint64_t HL[16]; // precalculated lo-half HTable
        uint64_t HH[16]; // precalculated hi-half HTable
 
        /*
         * Htable has 32 uint64_t variables at its disposal. The caller
         * uses the HL[0] as start point and the function below can consume
         * HL[] and HH[] from the variable definitions above.
         */
        void (*gcm_gmult_accel)(uint64_t Xi[2], const uint64_t *Htable);
 
        /* y and buf must be aligned to 64 bits due to accel */
        uint8_t y[16]; // the current cipher-input IV|Counter value
        uint8_t buf[16]; // buf working value
 
        uint8_t base_ectr[16]; // first counter-mode cipher output for tag
        uint8_t ectr[16]; // CTR ciphertext
 
        uint8_t rem_aad_inserted : 1; // Was remaining AAD inserted?
};
 
struct lc_aes_gcm_cryptor {
        struct lc_gcm_ctx gcm_ctx;
        struct lc_sym_ctx sym_ctx;
};
 
#define LC_AES_GCM_CTX_COMMON_SIZE                                             \
        (sizeof(struct lc_aead) + sizeof(struct lc_aes_gcm_cryptor))
 
#define LC_AES_GCM_STATE_SIZE(x) (LC_SYM_STATE_SIZE(x))
#define LC_AES_GCM_CTX_SIZE                                                    \
        (LC_AES_GCM_CTX_COMMON_SIZE + LC_AES_GCM_STATE_SIZE(lc_aes))
 
#define LC_AES_GCM_STATE_SIZE_LEN(len) (LC_SYM_STATE_SIZE_LEN(len))
#define LC_AES_GCM_CTX_SIZE_LEN(len)                                           \
        (LC_AES_GCM_CTX_COMMON_SIZE + LC_AES_GCM_STATE_SIZE_LEN(len))
 
/* AES-CBC with HMAC based AEAD-algorithm */
extern const struct lc_aead *lc_aes_gcm_aead;
 
#define _LC_AES_GCM_SET_CTX(name)                                              \
        _LC_SYM_SET_CTX((&name->sym_ctx), lc_aes, name,                        \
                        (sizeof(struct lc_aes_gcm_cryptor)))
 
#define LC_AES_GCM_SET_CTX(name)                                               \
        LC_AEAD_CTX(name, lc_aes_gcm_aead);                                    \
        _LC_AES_GCM_SET_CTX(((struct lc_aes_gcm_cryptor *)name->aead_state))

int lc_aes_gcm_alloc(struct lc_aead_ctx **ctx);
 
enum lc_aes_gcm_iv_type {
        lc_aes_gcm_iv_generate_new,
};

int lc_aes_gcm_generate_iv(struct lc_aead_ctx *ctx, const uint8_t *fixed_field,
                           size_t fixed_field_len, uint8_t *iv, size_t ivlen,
                           enum lc_aes_gcm_iv_type type);

#define LC_AES_GCM_CTX_ON_STACK(name)                                               \
        _Pragma("GCC diagnostic push")                                              \
                _Pragma("GCC diagnostic ignored \"-Wvla\"") _Pragma(                \
                        "GCC diagnostic ignored \"-Wdeclaration-after-statement\"") \
                        LC_ALIGNED_BUFFER(name##_ctx_buf, LC_AES_GCM_CTX_SIZE,      \
                                          LC_MEM_COMMON_ALIGNMENT);                 \
        struct lc_aead_ctx *name = (struct lc_aead_ctx *)name##_ctx_buf;            \
        LC_AES_GCM_SET_CTX(name);                                                   \
        lc_aead_zero(name);                                                         \
        _Pragma("GCC diagnostic pop")
 
#ifdef __cplusplus
}
#endif
 
#endif /* LC_AES_GCM_H */