EdDsa: check private value after sign

Check the private value hasn't changed during signing with EdDSA.

Author: SparkiDev

wolfcrypt/src/ed25519.c

@@ -22,6 +22,12 @@
 
  /* Based On Daniel J Bernstein's ed25519 Public Domain ref10 work. */
 
+
+/* Possible Ed25519 enable options:
+ *   WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN                               Default: OFF
+ *     Check that the private key didn't change during the signing operations.
+ */
+
 #ifdef HAVE_CONFIG_H
     #include <config.h>
 #endif
@@ -304,6 +310,9 @@ int wc_ed25519_sign_msg_ex(const byte* in, word32 inLen, byte* out,
     ALIGN16 byte nonce[WC_SHA512_DIGEST_SIZE];
     ALIGN16 byte hram[WC_SHA512_DIGEST_SIZE];
     ALIGN16 byte az[ED25519_PRV_KEY_SIZE];
+#ifdef WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN
+    byte orig_k[ED25519_KEY_SIZE];
+#endif
 
     /* sanity check on arguments */
     if (in == NULL || out == NULL || outLen == NULL || key == NULL ||
@@ -331,6 +340,10 @@ int wc_ed25519_sign_msg_ex(const byte* in, word32 inLen, byte* out,
     }
     *outLen = ED25519_SIG_SIZE;
 
+#ifdef WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN
+    XMEMCPY(orig_k, key->k, ED25519_KEY_SIZE);
+#endif
+
     /* step 1: create nonce to use where nonce is r in
        r = H(h_b, ... ,h_2b-1,M) */
     ret = ed25519_hash(key, key->k, ED25519_KEY_SIZE, az);
@@ -441,6 +454,18 @@ int wc_ed25519_sign_msg_ex(const byte* in, word32 inLen, byte* out,
     sc_muladd(out + (ED25519_SIG_SIZE/2), hram, az, nonce);
 #endif
 #endif /* WOLFSSL_SE050 */
+
+#ifdef WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN
+    {
+        int  i;
+        byte c = 0;
+        for (i = 0; i < ED25519_KEY_SIZE; i++) {
+            c |= key->k[i] ^ orig_k[i];
+        }
+        ret = ctMaskGT(c, 0) & SIG_VERIFY_E;
+    }
+#endif
+
     return ret;
 }
 

wolfcrypt/src/ed448.c

@@ -25,6 +25,11 @@
  * Reworked for curve448 by Sean Parkinson.
  */
 
+/* Possible Ed448 enable options:
+ *   WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN                               Default: OFF
+ *     Check that the private key didn't change during the signing operations.
+ */
+
 #ifdef HAVE_CONFIG_H
     #include <config.h>
 #endif
@@ -279,6 +284,9 @@ int wc_ed448_sign_msg_ex(const byte* in, word32 inLen, byte* out,
     byte     hram[ED448_SIG_SIZE];
     byte     az[ED448_PRV_KEY_SIZE];
     int      ret = 0;
+#ifdef WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN
+    byte     orig_k[ED448_KEY_SIZE];
+#endif
 
     /* sanity check on arguments */
     if ((in == NULL) || (out == NULL) || (outLen == NULL) || (key == NULL) ||
@@ -298,6 +306,10 @@ int wc_ed448_sign_msg_ex(const byte* in, word32 inLen, byte* out,
     if (ret == 0) {
         *outLen = ED448_SIG_SIZE;
 
+#ifdef WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN
+        XMEMCPY(orig_k, key->k, ED448_KEY_SIZE);
+#endif
+
         /* step 1: create nonce to use where nonce is r in
            r = H(h_b, ... ,h_2b-1,M) */
         ret = ed448_hash(key, key->k, ED448_KEY_SIZE, az, sizeof(az));
@@ -391,6 +403,17 @@ int wc_ed448_sign_msg_ex(const byte* in, word32 inLen, byte* out,
         sc448_muladd(out + (ED448_SIG_SIZE/2), hram, az, nonce);
     }
 
+#ifdef WOLFSSL_EDDSA_CHECK_PRIV_ON_SIGN
+    if (ret == 0) {
+        int  i;
+        byte c = 0;
+        for (i = 0; i < ED448_KEY_SIZE; i++) {
+            c |= key->k[i] ^ orig_k[i];
+        }
+        ret = ctMaskGT(c, 0) & SIG_VERIFY_E;
+    }
+#endif
+
     return ret;
 }
 

wolfssl/wolfcrypt/ed448.h

@@ -80,7 +80,7 @@ enum {
 /* An ED448 Key */
 struct ed448_key {
     byte    p[ED448_PUB_KEY_SIZE]; /* compressed public key */
-    byte    k[ED448_PRV_KEY_SIZE]; /* private key : 56 secret -- 56 public */
+    byte    k[ED448_PRV_KEY_SIZE]; /* private key : 57 secret -- 57 public */
 #ifdef FREESCALE_LTC_ECC
     /* uncompressed point coordinates */
     byte pointX[ED448_KEY_SIZE]; /* recovered X coordinate */