AES_XTS_IVSIZE
bcopy(iv, tweak, AES_XTS_IVSIZE);
bzero(tweak + AES_XTS_IVSIZE, AES_XTS_IVSIZE);
bcopy(iv, tweak, AES_XTS_IVSIZE);
bzero(tweak + AES_XTS_IVSIZE, AES_XTS_IVSIZE);
bzero(ctx->tweak + AES_XTS_IVSIZE, AES_XTS_IVSIZE);
bcopy(iv, &blocknum, AES_XTS_IVSIZE);
for (i = 0; i < AES_XTS_IVSIZE; i++) {