tlsprf.hpp

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//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012- OpenVPN Inc.
//
//    SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//
 
// Implement the TLS-PRF function, used by ProtoContext.
 
#ifndef OPENVPN_SSL_TLSPRF_H
#define OPENVPN_SSL_TLSPRF_H
 
#include <cstring> // for std::strlen and others
 
#include <string>
#include <sstream>
 
#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/common/rc.hpp>
#include <openvpn/common/hexstr.hpp>
#include <openvpn/common/unreachable.hpp>
#include <openvpn/buffer/buffer.hpp>
#include <openvpn/buffer/bufcomplete.hpp>
#include <openvpn/crypto/static_key.hpp>
#include <openvpn/crypto/cryptoalgs.hpp>
#include <openvpn/ssl/psid.hpp>
#include <openvpn/random/randapi.hpp>
 
namespace openvpn {
 
template <typename CRYPTO_API>
class TLSPRF
{
  public:
    OPENVPN_SIMPLE_EXCEPTION(tlsprf_uninitialized);
    OPENVPN_SIMPLE_EXCEPTION(tlsprf_client_server_mismatch);
    OPENVPN_SIMPLE_EXCEPTION(tlsprf_tlsprf_failed);
    enum
    {
        SIZE_OF_RANDOM = 32
    };
 
    TLSPRF(const bool server)
        : initialized_(false), server_(server)
    {
    }
 
    void randomize(StrongRandomAPI &rng)
    {
        if (!server_)
            rng.rand_bytes(pre_master, sizeof(pre_master));
        rng.rand_bytes(random1, sizeof(random1));
        rng.rand_bytes(random2, sizeof(random2));
        initialized_ = true;
    }
 
    void read(Buffer &buf)
    {
        if (!server_)
            buf.read(pre_master, sizeof(pre_master));
        buf.read(random1, sizeof(random1));
        buf.read(random2, sizeof(random2));
        initialized_ = true;
    }
 
    bool read_complete(BufferComplete &bc)
    {
        size_t need = sizeof(random1) + sizeof(random2);
        if (!server_)
            need += sizeof(pre_master);
        if (!bc.advance(need))
            return false;
        return true;
    }
 
    void write(Buffer &buf)
    {
        verify_initialized();
        if (!server_)
            buf.write(pre_master, sizeof(pre_master));
        buf.write(random1, sizeof(random1));
        buf.write(random2, sizeof(random2));
    }
 
    void generate_key_expansion(OpenVPNStaticKey &dest,
                                const TLSPRF &peer,
                                const ProtoSessionID &psid_self,
                                const ProtoSessionID &psid_peer) const
    {
        if (server_ == peer.server_)
            throw tlsprf_client_server_mismatch();
        if (server_)
            gen_exp(dest, peer, psid_peer, *this, psid_self);
        else
            gen_exp(dest, *this, psid_self, peer, psid_peer);
    }
 
    void erase()
    {
        if (initialized_)
        {
            if (!server_)
                std::memset(pre_master, 0, sizeof(pre_master));
            std::memset(random1, 0, sizeof(random1));
            std::memset(random2, 0, sizeof(random2));
            initialized_ = false;
        }
    }
 
    std::string dump(const char *title)
    {
        std::ostringstream out;
        out << "*** TLSPRF " << title << " pre_master: " << render_hex(pre_master, sizeof(pre_master)) << std::endl;
        out << "*** TLSPRF " << title << " random1: " << render_hex(random1, sizeof(random1)) << std::endl;
        out << "*** TLSPRF " << title << " random2: " << render_hex(random2, sizeof(random2)) << std::endl;
        return out.str();
    }
 
    ~TLSPRF()
    {
        erase();
    }
 
    static void openvpn_PRF(const unsigned char *secret,
                            const size_t secret_len,
                            const char *label,
                            const unsigned char *client_seed,
                            const size_t client_seed_len,
                            const unsigned char *server_seed,
                            const size_t server_seed_len,
                            const ProtoSessionID *client_sid,
                            const ProtoSessionID *server_sid,
                            unsigned char *output,
                            const size_t output_len)
    {
        const size_t label_len = std::strlen(label);
        // GCC is bad at optimizing this, so give it a hint
        if (client_seed_len != SIZE_OF_RANDOM || server_seed_len != SIZE_OF_RANDOM)
            unreachable();
        BufferAllocated seed(label_len
                                 + client_seed_len
                                 + server_seed_len
                                 + ProtoSessionID::SIZE * 2,
                             BufAllocFlags::DESTRUCT_ZERO);
        seed.write((unsigned char *)label, label_len);
        seed.write(client_seed, client_seed_len);
        seed.write(server_seed, server_seed_len);
        if (client_sid)
            client_sid->write(seed);
        if (server_sid)
            server_sid->write(seed);
 
        // compute PRF
        if (!CRYPTO_API::TLS1PRF::PRF(seed.data(),
                                      seed.size(),
                                      secret,
                                      secret_len,
                                      output,
                                      output_len))
        {
            throw tlsprf_tlsprf_failed();
        }
    }
 
  private:
    static void gen_exp(OpenVPNStaticKey &dest,
                        const TLSPRF &client,
                        const ProtoSessionID &psid_client,
                        const TLSPRF &server,
                        const ProtoSessionID &psid_server)
    {
        static const char master_secret_id[] = "OpenVPN master secret";
        static const char key_expansion_id[] = "OpenVPN key expansion";
 
        unsigned char master[48];
 
        client.verify_initialized();
        server.verify_initialized();
 
        // compute master secret
        openvpn_PRF(client.pre_master,
                    sizeof(client.pre_master),
                    master_secret_id,
                    client.random1,
                    sizeof(client.random1),
                    server.random1,
                    sizeof(server.random1),
                    nullptr,
                    nullptr,
                    master,
                    sizeof(master));
 
        // compute key expansion */
        openvpn_PRF(master,
                    sizeof(master),
                    key_expansion_id,
                    client.random2,
                    sizeof(client.random2),
                    server.random2,
                    sizeof(server.random2),
                    &psid_client,
                    &psid_server,
                    dest.raw_alloc(),
                    OpenVPNStaticKey::KEY_SIZE);
 
        std::memset(master, 0, sizeof(master));
    }
 
    void verify_initialized() const
    {
        if (!initialized_)
            throw tlsprf_uninitialized();
    }
 
    bool initialized_;
    bool server_;
    unsigned char pre_master[48];          // client generated
    unsigned char random1[SIZE_OF_RANDOM]; // generated by both client and server
    unsigned char random2[SIZE_OF_RANDOM]; // generated by both client and server
};
 
// TLSPRF wrapper API using dynamic polymorphism
 
class TLSPRFInstance : public RC<thread_unsafe_refcount>
{
  public:
    typedef RCPtr<TLSPRFInstance> Ptr;
 
    virtual void self_randomize(StrongRandomAPI &rng) = 0;
    virtual void self_write(Buffer &buf) = 0;
    virtual void peer_read(Buffer &buf) = 0;
    virtual bool peer_read_complete(BufferComplete &bc) = 0;
    virtual void erase() = 0;
 
    // clang-format off
    virtual void generate_key_expansion(OpenVPNStaticKey &dest,
                                        const ProtoSessionID &psid_self,
                                        const ProtoSessionID &psid_peer) const = 0;
    // clang-format on
};
 
class TLSPRFFactory : public RC<thread_unsafe_refcount>
{
  public:
    typedef RCPtr<TLSPRFFactory> Ptr;
 
    virtual TLSPRFInstance::Ptr new_obj(const bool self_is_server) = 0;
};
 
// TLSPRF wrapper implementation using dynamic polymorphism
 
template <typename CRYPTO_API>
class CryptoTLSPRFInstance : public TLSPRFInstance
{
  public:
    CryptoTLSPRFInstance(const bool self_is_server)
        : self(self_is_server),
          peer(!self_is_server)
    {
    }
 
    void self_randomize(StrongRandomAPI &rng) override
    {
        self.randomize(rng);
    }
 
    void self_write(Buffer &buf) override
    {
        self.write(buf);
    }
 
    void peer_read(Buffer &buf) override
    {
        peer.read(buf);
    }
 
    bool peer_read_complete(BufferComplete &bc) override
    {
        return peer.read_complete(bc);
    }
 
    void erase() override
    {
        self.erase();
        peer.erase();
    }
 
    void generate_key_expansion(OpenVPNStaticKey &dest,
                                const ProtoSessionID &psid_self,
                                const ProtoSessionID &psid_peer) const override
    {
        self.generate_key_expansion(dest, peer, psid_self, psid_peer);
    }
 
  private:
    TLSPRF<CRYPTO_API> self;
    TLSPRF<CRYPTO_API> peer;
};
 
template <typename CRYPTO_API>
class CryptoTLSPRFFactory : public TLSPRFFactory
{
  public:
    TLSPRFInstance::Ptr new_obj(const bool self_is_server) override
    {
        return new CryptoTLSPRFInstance<CRYPTO_API>(self_is_server);
    }
};
 
} // namespace openvpn
 
#endif // OPENVPN_SSL_TLSPRF_H