From ae3e85813614402347f143bd1df3caa148a5a48e Mon Sep 17 00:00:00 2001
From: Richard Moore <me@ricmoo.com>
Date: Wed, 20 May 2015 12:02:51 -0400
Subject: [PATCH] Added error checking to uECC_compute_public_key.

---
 test/test_compute.c | 23 ++++++++++++++++++-----
 uECC.c              | 26 +++++++++++++++++++++++---
 uECC.h              |  4 +++-
 3 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/test/test_compute.c b/test/test_compute.c
index 160fac5..88b6703 100644
--- a/test/test_compute.c
+++ b/test/test_compute.c
@@ -17,12 +17,13 @@ void vli_print(uint8_t *p_vli, unsigned int p_size)
 int main()
 {
     int i;
-    
+    int success;
+
     uint8_t l_private[uECC_BYTES];
-    
+
     uint8_t l_public[uECC_BYTES * 2];
     uint8_t l_public_computed[uECC_BYTES * 2];
-    
+
     printf("Testing 256 random private key pairs\n");
 
     for(i=0; i<256; ++i)
@@ -36,7 +37,10 @@ int main()
             return 1;
         }
 
-        uECC_compute_public_key(l_private, l_public_computed);
+        success = uECC_compute_public_key(l_private, l_public_computed);
+        if (!success) {
+            printf("uECC_compute_public_key() failed\n");
+        }
 
         if(memcmp(l_public, l_public_computed, sizeof(l_public)) != 0)
         {
@@ -52,7 +56,16 @@ int main()
             printf("\n");
         }
     }
+
     printf("\n");
-    
+
+    printf("Testing private key = 0\n");
+
+    memset(l_private, 0, uECC_BYTES);
+    success = uECC_compute_public_key(l_private, l_public_computed);
+    if (success) {
+        printf("uECC_compute_public_key() should have failed\n");
+    }
+
     return 0;
 }
diff --git a/uECC.c b/uECC.c
index 33cae0c..dd9da34 100644
--- a/uECC.c
+++ b/uECC.c
@@ -2380,16 +2380,36 @@ int uECC_verify(const uint8_t p_publicKey[uECC_BYTES*2], const uint8_t p_hash[uE
     return vli_equal(rx, r);
 }
 
-void uECC_compute_public_key(const uint8_t p_privateKey[uECC_BYTES], uint8_t p_publicKey[uECC_BYTES * 2]) {
-    EccPoint l_public;
+int uECC_compute_public_key(const uint8_t p_privateKey[uECC_BYTES], uint8_t p_publicKey[uECC_BYTES * 2]) {
     uECC_word_t l_private[uECC_WORDS];
-
     vli_bytesToNative(l_private, p_privateKey);
 
+    /* Make sure the private key is in the range [1, n-1]. */
+    if(vli_isZero(l_private))
+    {
+        return 0;
+    }
+
+#if uECC_CURVE != uECC_secp160r1
+    if(vli_cmp(curve_n, l_private) != 1)
+    {
+        return 0;
+    }
+#endif
+
+    /* Compute the public point */
+    EccPoint l_public;
     EccPoint_mult(&l_public, &curve_G, l_private, 0, vli_numBits(l_private, uECC_WORDS));
 
+    if (EccPoint_isZero(&l_public))
+    {
+        return 0;
+    }
+
     vli_nativeToBytes(p_publicKey, l_public.x);
     vli_nativeToBytes(p_publicKey + uECC_BYTES, l_public.y);
+
+    return 1;
 }
 
 int uECC_bytes(void)
diff --git a/uECC.h b/uECC.h
index ace1f4e..4787457 100644
--- a/uECC.h
+++ b/uECC.h
@@ -186,8 +186,10 @@ Inputs:
 
 Outputs:
     p_publicKey - Will be filled in with the corresponding public key
+
+Returns 1 if the key was computed successfully, 0 if an error occurred.
 */
-void uECC_compute_public_key(const uint8_t p_privateKey[uECC_BYTES], uint8_t p_publicKey[uECC_BYTES * 2]);
+int uECC_compute_public_key(const uint8_t p_privateKey[uECC_BYTES], uint8_t p_publicKey[uECC_BYTES * 2]);
 
 
 /* uECC_bytes() function.