curve25519.cpp

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/*
* Curve25519
* (C) 2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/curve25519.h>
#include <botan/internal/pk_ops_impl.h>
#include <botan/ber_dec.h>
#include <botan/der_enc.h>
#include <botan/rng.h>
 
namespace Botan {
 
void curve25519_basepoint(uint8_t mypublic[32], const uint8_t secret[32])
   {
   const uint8_t basepoint[32] = { 9 };
   curve25519_donna(mypublic, secret, basepoint);
   }
 
namespace {
 
void size_check(size_t size, const char* thing)
   {
   if(size != 32)
      throw Decoding_Error("Invalid size " + std::to_string(size) + " for Curve25519 " + thing);
   }
 
secure_vector<uint8_t> curve25519(const secure_vector<uint8_t>& secret,
                               const uint8_t pubval[32])
   {
   secure_vector<uint8_t> out(32);
   curve25519_donna(out.data(), secret.data(), pubval);
   return out;
   }
 
}
 
AlgorithmIdentifier Curve25519_PublicKey::algorithm_identifier() const
   {
   return AlgorithmIdentifier(get_oid(), AlgorithmIdentifier::USE_EMPTY_PARAM);
   }
 
bool Curve25519_PublicKey::check_key(RandomNumberGenerator& /*rng*/, bool /*strong*/) const
   {
   return true; // no tests possible?
   }
 
Curve25519_PublicKey::Curve25519_PublicKey(const AlgorithmIdentifier& /*unused*/,
                                           const std::vector<uint8_t>& key_bits)
   {
   m_public = key_bits;
 
   size_check(m_public.size(), "public key");
   }
 
std::vector<uint8_t> Curve25519_PublicKey::public_key_bits() const
   {
   return m_public;
   }
 
Curve25519_PrivateKey::Curve25519_PrivateKey(const secure_vector<uint8_t>& secret_key)
   {
   if(secret_key.size() != 32)
     throw Decoding_Error("Invalid size for Curve25519 private key");
 
   m_public.resize(32);
   m_private = secret_key;
   curve25519_basepoint(m_public.data(), m_private.data());
   }
 
Curve25519_PrivateKey::Curve25519_PrivateKey(RandomNumberGenerator& rng)
   {
   m_private = rng.random_vec(32);
   m_public.resize(32);
   curve25519_basepoint(m_public.data(), m_private.data());
   }
 
Curve25519_PrivateKey::Curve25519_PrivateKey(const AlgorithmIdentifier& /*unused*/,
                                             const secure_vector<uint8_t>& key_bits)
   {
   BER_Decoder(key_bits).decode(m_private, ASN1_Type::OctetString).discard_remaining();
 
   size_check(m_private.size(), "private key");
   m_public.resize(32);
   curve25519_basepoint(m_public.data(), m_private.data());
   }
 
std::unique_ptr<Public_Key> Curve25519_PrivateKey::public_key() const
   {
   return std::make_unique<Curve25519_PublicKey>(public_value());
   }
 
secure_vector<uint8_t> Curve25519_PrivateKey::private_key_bits() const
   {
   return DER_Encoder().encode(m_private, ASN1_Type::OctetString).get_contents();
   }
 
bool Curve25519_PrivateKey::check_key(RandomNumberGenerator& /*rng*/, bool /*strong*/) const
   {
   std::vector<uint8_t> public_point(32);
   curve25519_basepoint(public_point.data(), m_private.data());
   return public_point == m_public;
   }
 
secure_vector<uint8_t> Curve25519_PrivateKey::agree(const uint8_t w[], size_t w_len) const
   {
   size_check(w_len, "public value");
   return curve25519(m_private, w);
   }
 
namespace {
 
/**
* Curve25519 operation
*/
class Curve25519_KA_Operation final : public PK_Ops::Key_Agreement_with_KDF
   {
   public:
 
      Curve25519_KA_Operation(const Curve25519_PrivateKey& key, const std::string& kdf) :
         PK_Ops::Key_Agreement_with_KDF(kdf),
         m_key(key) {}
 
      size_t agreed_value_size() const override { return 32; }
 
      secure_vector<uint8_t> raw_agree(const uint8_t w[], size_t w_len) override
         {
         return m_key.agree(w, w_len);
         }
   private:
      const Curve25519_PrivateKey& m_key;
   };
 
}
 
std::unique_ptr<PK_Ops::Key_Agreement>
Curve25519_PrivateKey::create_key_agreement_op(RandomNumberGenerator& /*rng*/,
                                               const std::string& params,
                                               const std::string& provider) const
   {
   if(provider == "base" || provider.empty())
      return std::make_unique<Curve25519_KA_Operation>(*this, params);
   throw Provider_Not_Found(algo_name(), provider);
   }
 
}