cx_hkdf.c

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#ifdef HAVE_HMAC
#include "cx_hkdf.h"
#include "cx_hash.h"
#include "cx_hmac.h"
#include "cx_ram.h"
 
#include <string.h>
 
// HMAC-Based Key Kerivation Function defined at https://tools.ietf.org/html/rfc5869
// Used to implement the EIP-2333 for BLS12-381 key generation
 
void cx_hkdf_extract(const cx_md_t        hash_id,
                     const unsigned char *ikm,
                     unsigned int         ikm_len,
                     unsigned char       *salt,
                     unsigned int         salt_len,
                     unsigned char       *prk)
{
    cx_hmac_t            *hmac_ctx;
    const cx_hash_info_t *hash_info;
    size_t                md_len;
 
    hash_info = cx_hash_get_info(hash_id);
    md_len    = hash_info->output_size;
 
    hmac_ctx = &G_cx.hmac;
 
    if (salt == NULL) {
        memset(hmac_ctx->key, 0, md_len);
        salt     = hmac_ctx->key;
        salt_len = md_len;
    }
    if (cx_hmac_init(hmac_ctx, hash_id, salt, salt_len) != CX_OK
        || cx_hmac_update(hmac_ctx, ikm, ikm_len) != CX_OK
        || cx_hmac_final(hmac_ctx, prk, &md_len) != CX_OK) {
        return;
    }
}
 
void cx_hkdf_expand(const cx_md_t        hash_id,
                    const unsigned char *prk,
                    unsigned int         prk_len,
                    unsigned char       *info,
                    unsigned int         info_len,
                    unsigned char       *okm,
                    unsigned int         okm_len)
{
    unsigned char         i;
    unsigned int          offset = 0;
    unsigned char         T[MAX_HASH_SIZE];
    cx_hmac_t            *hmac_ctx;
    const cx_hash_info_t *hash_info;
    size_t                md_len;
 
    hash_info = cx_hash_get_info(hash_id);
    md_len    = hash_info->output_size;
 
    hmac_ctx = &G_cx.hmac;
 
    for (i = 1; okm_len > 0; i++) {
        if (cx_hmac_init(hmac_ctx, hash_id, prk, prk_len) != CX_OK) {
            return;
        }
        if (i > 1) {
            if (cx_hmac_update(hmac_ctx, T, offset) != CX_OK) {
                return;
            }
        }
        if (cx_hmac_update(hmac_ctx, info, info_len) != CX_OK
            || cx_hmac_update(hmac_ctx, &i, sizeof(i)) != CX_OK
            || cx_hmac_final(hmac_ctx, T, &md_len) != CX_OK) {
            return;
        }
 
        offset = (okm_len < md_len) ? okm_len : md_len;
        memcpy(okm + (i - 1) * md_len, T, offset);
        okm_len -= offset;
    }
}
#endif  // HAVE_HMAC