Added unittest to make sure future changes in P224EncryptedKeyExchange don't change output.

External implementations already expect this values.

BUG=438470
R=agl@chromium.org, gene@chromium.org

Review URL: https://codereview.chromium.org/789743002

Cr-Commit-Position: refs/heads/master@{#307654}

1 files changed, 16 insertions, 4 deletions

diff --git a/crypto/p224_spake.cc b/crypto/p224_spake.cc
index f20b10c..05fe68c 100644
--- a/crypto/p224_spake.cc
+++ b/crypto/p224_spake.cc
@@ -7,6 +7,8 @@
 
 #include <crypto/p224_spake.h>
 
+#include <algorithm>
+
 #include <base/logging.h>
 #include <crypto/p224.h>
 #include <crypto/random.h>
@@ -105,14 +107,18 @@ P224EncryptedKeyExchange::P224EncryptedKeyExchange(
   // x_ is a random scalar.
   RandBytes(x_, sizeof(x_));
 
-  // X = g**x_
-  p224::Point X;
-  p224::ScalarBaseMult(x_, &X);
-
   // Calculate |password| hash to get SPAKE password value.
   SHA256HashString(std::string(password.data(), password.length()),
                    pw_, sizeof(pw_));
 
+  Init();
+}
+
+void P224EncryptedKeyExchange::Init() {
+  // X = g**x_
+  p224::Point X;
+  p224::ScalarBaseMult(x_, &X);
+
   // The client masks the Diffie-Hellman value, X, by adding M**pw and the
   // server uses N**pw.
   p224::Point MNpw;
@@ -253,4 +259,10 @@ const std::string& P224EncryptedKeyExchange::GetUnverifiedKey() const {
   return key_;
 }
 
+void P224EncryptedKeyExchange::SetXForTesting(const std::string& x) {
+  memset(&x_, 0, sizeof(x_));
+  memcpy(&x_, x.data(), std::min(x.size(), sizeof(x_)));
+  Init();
+}
+
 }  // namespace crypto