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>
diff --git a/crypto/drbg.c b/crypto/drbg.c
index 0aca2b9..4ee1a9c 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -258,6 +258,7 @@
const struct drbg_string *in);
static int drbg_init_sym_kernel(struct drbg_state *drbg);
static int drbg_fini_sym_kernel(struct drbg_state *drbg);
+static int drbg_kcapi_sym_ctr(struct drbg_state *drbg, u8 *outbuf, u32 outlen);
/* BCC function for CTR DRBG as defined in 10.4.3 */
static int drbg_ctr_bcc(struct drbg_state *drbg,
@@ -482,35 +483,36 @@
drbg_blocklen(drbg);
unsigned char *temp_p, *df_data_p; /* pointer to iterate over buffers */
unsigned int len = 0;
- struct drbg_string cipherin;
if (3 > reseed)
memset(df_data, 0, drbg_statelen(drbg));
+ if (!reseed) {
+ /*
+ * The DRBG uses the CTR mode of the underlying AES cipher. The
+ * CTR mode increments the counter value after the AES operation
+ * but SP800-90A requires that the counter is incremented before
+ * the AES operation. Hence, we increment it at the time we set
+ * it by one.
+ */
+ crypto_inc(drbg->V, drbg_blocklen(drbg));
+
+ ret = crypto_skcipher_setkey(drbg->ctr_handle, drbg->C,
+ drbg_keylen(drbg));
+ if (ret)
+ goto out;
+ }
+
/* 10.2.1.3.2 step 2 and 10.2.1.4.2 step 2 */
if (seed) {
ret = drbg_ctr_df(drbg, df_data, drbg_statelen(drbg), seed);
if (ret)
goto out;
- drbg_kcapi_symsetkey(drbg, drbg->C);
}
- drbg_string_fill(&cipherin, drbg->V, drbg_blocklen(drbg));
- /*
- * 10.2.1.3.2 steps 2 and 3 are already covered as the allocation
- * zeroizes all memory during initialization
- */
- while (len < (drbg_statelen(drbg))) {
- /* 10.2.1.2 step 2.1 */
- crypto_inc(drbg->V, drbg_blocklen(drbg));
- /*
- * 10.2.1.2 step 2.2 */
- ret = drbg_kcapi_sym(drbg, temp + len, &cipherin);
- if (ret)
- goto out;
- /* 10.2.1.2 step 2.3 and 3 */
- len += drbg_blocklen(drbg);
- }
+ ret = drbg_kcapi_sym_ctr(drbg, temp, drbg_statelen(drbg));
+ if (ret)
+ return ret;
/* 10.2.1.2 step 4 */
temp_p = temp;
@@ -522,9 +524,14 @@
/* 10.2.1.2 step 5 */
memcpy(drbg->C, temp, drbg_keylen(drbg));
- drbg_kcapi_symsetkey(drbg, drbg->C);
+ ret = crypto_skcipher_setkey(drbg->ctr_handle, drbg->C,
+ drbg_keylen(drbg));
+ if (ret)
+ goto out;
/* 10.2.1.2 step 6 */
memcpy(drbg->V, temp + drbg_keylen(drbg), drbg_blocklen(drbg));
+ /* See above: increment counter by one to compensate timing of CTR op */
+ crypto_inc(drbg->V, drbg_blocklen(drbg));
ret = 0;
out:
@@ -543,46 +550,26 @@
unsigned char *buf, unsigned int buflen,
struct list_head *addtl)
{
- int len = 0;
- int ret = 0;
- struct drbg_string data;
+ int ret;
+ int len = min_t(int, buflen, INT_MAX);
/* 10.2.1.5.2 step 2 */
if (addtl && !list_empty(addtl)) {
ret = drbg_ctr_update(drbg, addtl, 2);
if (ret)
return 0;
- drbg_kcapi_symsetkey(drbg, drbg->C);
}
/* 10.2.1.5.2 step 4.1 */
- crypto_inc(drbg->V, drbg_blocklen(drbg));
- drbg_string_fill(&data, drbg->V, drbg_blocklen(drbg));
- while (len < buflen) {
- int outlen = 0;
- /* 10.2.1.5.2 step 4.2 */
- ret = drbg_kcapi_sym(drbg, drbg->scratchpad, &data);
- if (ret) {
- len = ret;
- goto out;
- }
- outlen = (drbg_blocklen(drbg) < (buflen - len)) ?
- drbg_blocklen(drbg) : (buflen - len);
- /* 10.2.1.5.2 step 4.3 */
- memcpy(buf + len, drbg->scratchpad, outlen);
- len += outlen;
- /* 10.2.1.5.2 step 6 */
- if (len < buflen)
- crypto_inc(drbg->V, drbg_blocklen(drbg));
- }
+ ret = drbg_kcapi_sym_ctr(drbg, buf, len);
+ if (ret)
+ return ret;
/* 10.2.1.5.2 step 6 */
ret = drbg_ctr_update(drbg, NULL, 3);
if (ret)
len = ret;
-out:
- memset(drbg->scratchpad, 0, drbg_blocklen(drbg));
return len;
}
@@ -1634,10 +1621,46 @@
#endif /* (CONFIG_CRYPTO_DRBG_HASH || CONFIG_CRYPTO_DRBG_HMAC) */
#ifdef CONFIG_CRYPTO_DRBG_CTR
+static int drbg_fini_sym_kernel(struct drbg_state *drbg)
+{
+ struct crypto_cipher *tfm =
+ (struct crypto_cipher *)drbg->priv_data;
+ if (tfm)
+ crypto_free_cipher(tfm);
+ drbg->priv_data = NULL;
+
+ if (drbg->ctr_handle)
+ crypto_free_skcipher(drbg->ctr_handle);
+ drbg->ctr_handle = NULL;
+
+ if (drbg->ctr_req)
+ skcipher_request_free(drbg->ctr_req);;
+ drbg->ctr_req = NULL;
+
+ kfree(drbg->ctr_null_value_buf);
+ drbg->ctr_null_value = NULL;
+
+ return 0;
+}
+
+static void drbg_skcipher_cb(struct crypto_async_request *req, int error)
+{
+ struct drbg_state *drbg = req->data;
+
+ if (error == -EINPROGRESS)
+ return;
+ drbg->ctr_async_err = error;
+ complete(&drbg->ctr_completion);
+}
+
+#define DRBG_CTR_NULL_LEN 128
static int drbg_init_sym_kernel(struct drbg_state *drbg)
{
- int ret = 0;
struct crypto_cipher *tfm;
+ struct crypto_skcipher *sk_tfm;
+ struct skcipher_request *req;
+ unsigned int alignmask;
+ char ctr_name[CRYPTO_MAX_ALG_NAME];
tfm = crypto_alloc_cipher(drbg->core->backend_cra_name, 0, 0);
if (IS_ERR(tfm)) {
@@ -1647,16 +1670,41 @@
}
BUG_ON(drbg_blocklen(drbg) != crypto_cipher_blocksize(tfm));
drbg->priv_data = tfm;
- return ret;
-}
-static int drbg_fini_sym_kernel(struct drbg_state *drbg)
-{
- struct crypto_cipher *tfm =
- (struct crypto_cipher *)drbg->priv_data;
- if (tfm)
- crypto_free_cipher(tfm);
- drbg->priv_data = NULL;
+ if (snprintf(ctr_name, CRYPTO_MAX_ALG_NAME, "ctr(%s)",
+ drbg->core->backend_cra_name) >= CRYPTO_MAX_ALG_NAME) {
+ drbg_fini_sym_kernel(drbg);
+ return -EINVAL;
+ }
+ sk_tfm = crypto_alloc_skcipher(ctr_name, 0, 0);
+ if (IS_ERR(sk_tfm)) {
+ pr_info("DRBG: could not allocate CTR cipher TFM handle: %s\n",
+ ctr_name);
+ drbg_fini_sym_kernel(drbg);
+ return PTR_ERR(sk_tfm);
+ }
+ drbg->ctr_handle = sk_tfm;
+
+ req = skcipher_request_alloc(sk_tfm, GFP_KERNEL);
+ if (!req) {
+ pr_info("DRBG: could not allocate request queue\n");
+ drbg_fini_sym_kernel(drbg);
+ return PTR_ERR(req);
+ }
+ drbg->ctr_req = req;
+ skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
+ drbg_skcipher_cb, drbg);
+
+ alignmask = crypto_skcipher_alignmask(sk_tfm);
+ drbg->ctr_null_value_buf = kzalloc(DRBG_CTR_NULL_LEN + alignmask,
+ GFP_KERNEL);
+ if (!drbg->ctr_null_value_buf) {
+ drbg_fini_sym_kernel(drbg);
+ return -ENOMEM;
+ }
+ drbg->ctr_null_value = (u8 *)PTR_ALIGN(drbg->ctr_null_value_buf,
+ alignmask + 1);
+
return 0;
}
@@ -1680,6 +1728,43 @@
crypto_cipher_encrypt_one(tfm, outval, in->buf);
return 0;
}
+
+static int drbg_kcapi_sym_ctr(struct drbg_state *drbg, u8 *outbuf, u32 outlen)
+{
+ struct scatterlist sg_in;
+
+ sg_init_one(&sg_in, drbg->ctr_null_value, DRBG_CTR_NULL_LEN);
+
+ while (outlen) {
+ u32 cryptlen = min_t(u32, outlen, DRBG_CTR_NULL_LEN);
+ struct scatterlist sg_out;
+ int ret;
+
+ sg_init_one(&sg_out, outbuf, cryptlen);
+ skcipher_request_set_crypt(drbg->ctr_req, &sg_in, &sg_out,
+ cryptlen, drbg->V);
+ ret = crypto_skcipher_encrypt(drbg->ctr_req);
+ switch (ret) {
+ case 0:
+ break;
+ case -EINPROGRESS:
+ case -EBUSY:
+ ret = wait_for_completion_interruptible(
+ &drbg->ctr_completion);
+ if (!ret && !drbg->ctr_async_err) {
+ reinit_completion(&drbg->ctr_completion);
+ break;
+ }
+ default:
+ return ret;
+ }
+ init_completion(&drbg->ctr_completion);
+
+ outlen -= cryptlen;
+ }
+
+ return 0;
+}
#endif /* CONFIG_CRYPTO_DRBG_CTR */
/***************************************************************