gistfile1.c

#define KEY_SIZE 32 /* AES has a maximum key size of 256 bits */
static char crypto_key[KEY_SIZE];
static int key_size = 0; /* size of the current key */

// Put a check that key size must be 16, 24 or 32 bytes long, required by AES.


static void sbd_transfer(struct sbd_device *dev, sector_t sector,
                unsigned long nsect, char *buffer, int write) {

... // check if key set
        }else{
                crypto_cipher_clear_flags(tfm, ~0);
                crypto_cipher_setkey(tfm, crypto_key, key_size);
        }

...
        if (write){
                if(key_size != 0){
                        for (k = 0; k < nbytes; k+=
                                                crypto_cipher_blocksize(tfm)) {
                                crypto_cipher_encrypt_one(tfm, dev->data+
                                                        offset+k, buffer+k);
                        }
                }else{
                        memcpy(dev->data + offset, buffer, nbytes);
                }
        }else{
                if(key_size != 0){
                        for (k = 0; k < nbytes; k+=
                                                crypto_cipher_blocksize(tfm)) {
                                crypto_cipher_decrypt_one(tfm, buffer+k,
                                                        dev->data+offset+k);
                        }
                }else{
                        memcpy(buffer, dev->data + offset, nbytes);
                }
        }
        
        
        
static int __init sbd_init(void) {
        
        tfm = crypto_alloc_cipher("aes", 0, 16);
        if (IS_ERR(tfm)){
                printk(KERN_ERR "alg: cipher: Failed to load transform");
                return PTR_ERR(tfm);
        }
        ...
        

static void __exit sbd_exit(void) {
        ...
        crypto_free_cipher(tfm);
        ...