crypto: drbg - use CTR AES instead of ECB AES

The CTR DRBG derives its random data from the CTR that is encrypted with
AES.

This patch now changes the CTR DRBG implementation such that the
CTR AES mode is employed. This allows the use of steamlined CTR AES
implementation such as ctr-aes-aesni.

Unfortunately there are the following subtile changes we need to apply
when using the CTR AES mode:

- the CTR mode increments the counter after the cipher operation, but
  the CTR DRBG requires the increment before the cipher op. Hence, the
  crypto_inc is applied to the counter (drbg->V) once it is
  recalculated.

- the CTR mode wants to encrypt data, but the CTR DRBG is interested in
  the encrypted counter only. The full CTR mode is the XOR of the
  encrypted counter with the plaintext data. To access the encrypted
  counter, the patch uses a NULL data vector as plaintext to be
  "encrypted".

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/crypto/drbg.h b/include/crypto/drbg.h
index d961b2b16f55..b2fe15d1ceba 100644
--- a/include/crypto/drbg.h
+++ b/include/crypto/drbg.h
@@ -43,6 +43,7 @@
 #include <linux/random.h>
 #include <linux/scatterlist.h>
 #include <crypto/hash.h>
+#include <crypto/skcipher.h>
 #include <linux/module.h>
 #include <linux/crypto.h>
 #include <linux/slab.h>
@@ -115,6 +116,14 @@ struct drbg_state {
 	 /* some memory the DRBG can use for its operation */
 	unsigned char *scratchpad;
 	void *priv_data;	/* Cipher handle */
+
+	struct crypto_skcipher *ctr_handle;	/* CTR mode cipher handle */
+	struct skcipher_request *ctr_req;	/* CTR mode request handle */
+	__u8 *ctr_null_value_buf;		/* CTR mode unaligned buffer */
+	__u8 *ctr_null_value;			/* CTR mode aligned zero buf */
+	struct completion ctr_completion;	/* CTR mode async handler */
+	int ctr_async_err;			/* CTR mode async error */
+
 	bool seeded;		/* DRBG fully seeded? */
 	bool pr;		/* Prediction resistance enabled? */
 	struct work_struct seed_work;	/* asynchronous seeding support */