crypto: ecdh - add privkey generation support

Add support for generating ecc private keys.

Generation of ecc private keys is helpful in a user-space to kernel
ecdh offload because the keys are not revealed to user-space. Private
key generation is also helpful to implement forward secrecy.

If the user provides a NULL ecc private key, the kernel will generate it
and further use it for ecdh.

Move ecdh's object files below drbg's. drbg must be present in the kernel
at the time of calling.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Stephan Müller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/Kconfig b/crypto/Kconfig
index aac4bc90a138e7f5cfc1c2b4faa871f1d0ba2e4e..caa770e535a2e5c01b7dd2455ed80378014b1ec9 100644 (file)
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -130,6 +130,7 @@ config CRYPTO_DH
 config CRYPTO_ECDH
        tristate "ECDH algorithm"
        select CRYTPO_KPP
+       select CRYPTO_RNG_DEFAULT
        help
          Generic implementation of the ECDH algorithm
 

diff --git a/crypto/Makefile b/crypto/Makefile
index 8a44057240d5ac5466ebdc39579aa35673b088e6..d41f0331b085ca8a4f78f6bb369b83e9a51e450e 100644 (file)
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -33,10 +33,6 @@ obj-$(CONFIG_CRYPTO_KPP2) += kpp.o
 dh_generic-y := dh.o
 dh_generic-y += dh_helper.o
 obj-$(CONFIG_CRYPTO_DH) += dh_generic.o
-ecdh_generic-y := ecc.o
-ecdh_generic-y += ecdh.o
-ecdh_generic-y += ecdh_helper.o
-obj-$(CONFIG_CRYPTO_ECDH) += ecdh_generic.o
 
 $(obj)/rsapubkey-asn1.o: $(obj)/rsapubkey-asn1.c $(obj)/rsapubkey-asn1.h
 $(obj)/rsaprivkey-asn1.o: $(obj)/rsaprivkey-asn1.c $(obj)/rsaprivkey-asn1.h
@@ -138,6 +134,11 @@ obj-$(CONFIG_CRYPTO_USER_API_SKCIPHER) += algif_skcipher.o
 obj-$(CONFIG_CRYPTO_USER_API_RNG) += algif_rng.o
 obj-$(CONFIG_CRYPTO_USER_API_AEAD) += algif_aead.o
 
+ecdh_generic-y := ecc.o
+ecdh_generic-y += ecdh.o
+ecdh_generic-y += ecdh_helper.o
+obj-$(CONFIG_CRYPTO_ECDH) += ecdh_generic.o
+
 #
 # generic algorithms and the async_tx api
 #

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 6c33c4323d6aed8aee2cf86fdde7fafb1aa93156..633a9bcdc5746ae46845529d3fff02a0260e2e42 100644 (file)
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -29,6 +29,7 @@
 #include <linux/swab.h>
 #include <linux/fips.h>
 #include <crypto/ecdh.h>
+#include <crypto/rng.h>
 
 #include "ecc.h"
 #include "ecc_curve_defs.h"
@@ -927,6 +928,61 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
        return 0;
 }
 
+/*
+ * ECC private keys are generated using the method of extra random bits,
+ * equivalent to that described in FIPS 186-4, Appendix B.4.1.
+ *
+ * d = (c mod(n–1)) + 1    where c is a string of random bits, 64 bits longer
+ *                         than requested
+ * 0 <= c mod(n-1) <= n-2  and implies that
+ * 1 <= d <= n-1
+ *
+ * This method generates a private key uniformly distributed in the range
+ * [1, n-1].
+ */
+int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
+{
+       const struct ecc_curve *curve = ecc_get_curve(curve_id);
+       u64 priv[ndigits];
+       unsigned int nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+       unsigned int nbits = vli_num_bits(curve->n, ndigits);
+       int err;
+
+       /* Check that N is included in Table 1 of FIPS 186-4, section 6.1.1 */
+       if (nbits < 160)
+               return -EINVAL;
+
+       /*
+        * FIPS 186-4 recommends that the private key should be obtained from a
+        * RBG with a security strength equal to or greater than the security
+        * strength associated with N.
+        *
+        * The maximum security strength identified by NIST SP800-57pt1r4 for
+        * ECC is 256 (N >= 512).
+        *
+        * This condition is met by the default RNG because it selects a favored
+        * DRBG with a security strength of 256.
+        */
+       if (crypto_get_default_rng())
+               err = -EFAULT;
+
+       err = crypto_rng_get_bytes(crypto_default_rng, (u8 *)priv, nbytes);
+       crypto_put_default_rng();
+       if (err)
+               return err;
+
+       if (vli_is_zero(priv, ndigits))
+               return -EINVAL;
+
+       /* Make sure the private key is in the range [1, n-1]. */
+       if (vli_cmp(curve->n, priv, ndigits) != 1)
+               return -EINVAL;
+
+       ecc_swap_digits(priv, privkey, ndigits);
+
+       return 0;
+}
+
 int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits,
                     const u64 *private_key, u64 *public_key)
 {

diff --git a/crypto/ecc.h b/crypto/ecc.h
index e13fe8800ee8dde50879c558d3bc67b8cb1ac5c1..e4fd4492c765f0d2031b6a276c6b85d74edd9375 100644 (file)
--- a/crypto/ecc.h
+++ b/crypto/ecc.h
@@ -43,6 +43,20 @@
 int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
                     const u64 *private_key, unsigned int private_key_len);
 
+/**
+ * ecc_gen_privkey() -  Generates an ECC private key.
+ * The private key is a random integer in the range 0 < random < n, where n is a
+ * prime that is the order of the cyclic subgroup generated by the distinguished
+ * point G.
+ * @curve_id:          id representing the curve to use
+ * @ndigits:           curve number of digits
+ * @private_key:       buffer for storing the generated private key
+ *
+ * Returns 0 if the private key was generated successfully, a negative value
+ * if an error occurred.
+ */
+int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey);
+
 /**
  * ecc_make_pub_key() - Compute an ECC public key
  *

diff --git a/crypto/ecdh.c b/crypto/ecdh.c
index 4aa0b0cb462788f4485616253a2ade8e6b01ea95..61c7708905d01ec6745c03352579b2173fc6c87f 100644 (file)
--- a/crypto/ecdh.c
+++ b/crypto/ecdh.c
@@ -55,6 +55,10 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
        ctx->curve_id = params.curve_id;
        ctx->ndigits = ndigits;
 
+       if (!params.key || !params.key_size)
+               return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
+                                      ctx->private_key);
+
        if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
                             (const u64 *)params.key, params.key_size) < 0)
                return -EINVAL;