net: add low-entropy, shared secret authentication protocol.

crypto/p224.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CRYPTO_P224_H_
 #define CRYPTO_P224_H_
 #pragma once
 
 #include <string>
 
@@ skipping 18 matching lines @@
   // number < p.
   bool SetFromString(const base::StringPiece& in);
 
   // ToString returns an external representation of the Point.
   std::string ToString() const;
 
   // An Point is represented in Jacobian form (x/z², y/z³).
   FieldElement x, y, z;
 };
 
+// kScalarBytes is the number of bytes needed to represent an element of the
+// P224 field.
+static const size_t kScalarBytes = 28;
+
 // ScalarMult computes *out = in*scalar where scalar is a 28-byte, big-endian
 // number.
 void CRYPTO_EXPORT ScalarMult(const Point& in, const uint8* scalar, Point* out);
 
 // ScalarBaseMult computes *out = g*scalar where g is the base point of the
 // curve and scalar is a 28-byte, big-endian number.
 void CRYPTO_EXPORT ScalarBaseMult(const uint8* scalar, Point* out);
 
 // Add computes *out = a+b.
 void CRYPTO_EXPORT Add(const Point& a, const Point& b, Point* out);
 
 // Negate calculates out = -a;
 void CRYPTO_EXPORT Negate(const Point& a, Point* out);
 
 }  // namespace p224
 
 }  // namespace crypto
 
 #endif  // CRYPTO_P224_H_