#include <crypto/internal/hash.h>
#include <linux/module.h>

#define SHA256_LENGTH 32

static void show_hash_result(char *plaintext, char *hash_sha256)
{
    int i;
    char str[SHA256_LENGTH * 2 + 1];

    pr_info("sha256 test for string: \"%s\"\n", plaintext);
    for (i = 0; i < SHA256_LENGTH; i++)
        sprintf(&str[i * 2], "%02x", (unsigned char) hash_sha256[i]);
    str[i * 2] = 0;
    pr_info("%s\n", str);
}

int cryptosha256_init(void)
{
    char *plaintext = "This is a test";
    char hash_sha256[SHA256_LENGTH];
    struct crypto_shash *sha256;
    struct shash_desc *shash;

    sha256 = crypto_alloc_shash("sha256", 0, 0);
    if (IS_ERR(sha256))
        return -1;

    shash = kmalloc(sizeof(struct shash_desc) + crypto_shash_descsize(sha256),
                    GFP_KERNEL);
    if (!shash)
        return -ENOMEM;

    shash->tfm = sha256;

    if (crypto_shash_init(shash))
        return -1;

    if (crypto_shash_update(shash, plaintext, strlen(plaintext)))
        return -1;

    if (crypto_shash_final(shash, hash_sha256))
        return -1;

    kfree(shash);
    crypto_free_shash(sha256);

    show_hash_result(plaintext, hash_sha256);

    return 0;
}

void cryptosha256_exit(void) {}

module_init(cryptosha256_init);
module_exit(cryptosha256_exit);

MODULE_DESCRIPTION("sha256 hash test");
MODULE_LICENSE("GPL");