From a46621eb5789749e0e54e97fb6d95390c712a27d Mon Sep 17 00:00:00 2001
From: Richard Moore <me@ricmoo.com>
Date: Tue, 19 May 2015 13:26:24 -0400
Subject: [PATCH] Added uECC_compute_public_key.

---
 test/test_compute.c | 58 +++++++++++++++++++++++++++++++++++++++++++++
 uECC.c              | 12 ++++++++++
 uECC.h              | 12 ++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 test/test_compute.c

diff --git a/test/test_compute.c b/test/test_compute.c
new file mode 100644
index 0000000..160fac5
--- /dev/null
+++ b/test/test_compute.c
@@ -0,0 +1,58 @@
+/* Copyright 2014, Kenneth MacKay. Licensed under the BSD 2-clause license. */
+
+#include "uECC.h"
+
+#include <stdio.h>
+#include <string.h>
+
+void vli_print(uint8_t *p_vli, unsigned int p_size)
+{
+    while(p_size)
+    {
+        printf("%02X ", (unsigned)p_vli[p_size - 1]);
+        --p_size;
+    }
+}
+
+int main()
+{
+    int i;
+    
+    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)
+    {
+        printf(".");
+        fflush(stdout);
+
+        int success = uECC_make_key(l_public, l_private);
+        if (!success) {
+            printf("uECC_make_key() failed\n");
+            return 1;
+        }
+
+        uECC_compute_public_key(l_private, l_public_computed);
+
+        if(memcmp(l_public, l_public_computed, sizeof(l_public)) != 0)
+        {
+            printf("Computed and provided public keys are not identical!\n");
+            printf("Computed public key = ");
+            vli_print(l_public_computed, uECC_BYTES);
+            printf("\n");
+            printf("Provided public key = ");
+            vli_print(l_public, uECC_BYTES);
+            printf("\n");
+            printf("Private key = ");
+            vli_print(l_private, uECC_BYTES);
+            printf("\n");
+        }
+    }
+    printf("\n");
+    
+    return 0;
+}
diff --git a/uECC.c b/uECC.c
index 96726a9..33cae0c 100644
--- a/uECC.c
+++ b/uECC.c
@@ -2380,6 +2380,18 @@ 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;
+    uECC_word_t l_private[uECC_WORDS];
+
+    vli_bytesToNative(l_private, p_privateKey);
+
+    EccPoint_mult(&l_public, &curve_G, l_private, 0, vli_numBits(l_private, uECC_WORDS));
+
+    vli_nativeToBytes(p_publicKey, l_public.x);
+    vli_nativeToBytes(p_publicKey + uECC_BYTES, l_public.y);
+}
+
 int uECC_bytes(void)
 {
     return uECC_BYTES;
diff --git a/uECC.h b/uECC.h
index 18c1adb..e1a4fa8 100644
--- a/uECC.h
+++ b/uECC.h
@@ -178,6 +178,18 @@ Returns 1 if the public key is valid, 0 if it is invalid.
 */
 int uECC_valid_public_key(const uint8_t p_publicKey[uECC_BYTES*2]);
 
+/* uECC_compute_public_key() function.
+Compute the corresponding public key for a private key.
+
+Inputs:
+    p_privateKey - The private key to compute the public key for
+
+Outputs:
+    p_publicKey - Will be filled in with the corresponding public key
+*/
+void uECC_compute_public_key(const uint8_t p_privateKey[uECC_BYTES], uint8_t p_publicKey[uECC_BYTES * 2]);
+
+
 /* uECC_bytes() function.
 Returns the value of uECC_BYTES. Helpful for foreign-interfaces to higher-level languages.
 */