ECIES: add HKDF (specified in RFC 5869) using HMAC-SHA256

Change-Id: I18cf63b6454d3d11386e9de93d934d759e0abc0e
diff --git a/google_keymaster_test_utils.cpp b/google_keymaster_test_utils.cpp
index 0f5db5f..664e020 100644
--- a/google_keymaster_test_utils.cpp
+++ b/google_keymaster_test_utils.cpp
@@ -99,6 +99,35 @@
     }
 }
 
+static char hex_value[256] = {
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  1,  2,  3,  4,  5,  6, 7, 8, 9, 0, 0, 0, 0, 0, 0,  // '0'..'9'
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 'A'..'F'
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 'a'..'f'
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
+string hex2str(string a) {
+    string b;
+    size_t num = a.size()/2;
+    b.resize(num);
+    for (size_t i = 0; i < num; i++) {
+        b[i] = (hex_value[a[i * 2] & 0xFF] << 4) + (hex_value[a[i * 2 + 1] & 0xFF]);
+    }
+    return b;
+}
+
 namespace keymaster {
 
 bool operator==(const AuthorizationSet& a, const AuthorizationSet& b) {