
Introduce CTR mode support for the cipher APIs. CTR mode uses a counter rather than a traditional IV. The counter has additional properties, including a nonce and initial counter block. We reuse the ctx->iv as the counter for conveniences. Both libgcrypt and nettle are support CTR mode, the cipher-builtin doesn't support yet. Signed-off-by: Gonglei <arei.gonglei@huawei.com> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>