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357
ssh/ssh_key_exchange.cc
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357
ssh/ssh_key_exchange.cc
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/*
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* Copyright (c) 2012 Juli Mallett. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <openssl/bn.h>
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#include <openssl/dh.h>
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#include <common/buffer.h>
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#include <crypto/crypto_hash.h>
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#include <event/event_callback.h>
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#include <ssh/ssh_algorithm_negotiation.h>
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#include <ssh/ssh_key_exchange.h>
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#include <ssh/ssh_protocol.h>
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#include <ssh/ssh_server_host_key.h>
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#include <ssh/ssh_session.h>
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#include <ssh/ssh_filter.h>
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////////////////////////////////////////////////////////////////////////////////
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// //
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// File: ssh_key_exchange.cc //
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// Description: SSH key check performed on filter session start //
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// Project: WANProxy XTech //
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// Adapted by: Andreu Vidal Bramfeld-Software //
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// Last modified: 2015-04-01 //
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// //
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////////////////////////////////////////////////////////////////////////////////
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#define DH_GROUP_MIN 1024
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#define DH_GROUP_MAX 8192
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#define USE_TEST_GROUP
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namespace {
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#ifdef USE_TEST_GROUP
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static uint8_t test_prime_and_generator[] = {
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0x00, 0x00, 0x00, 0x81, 0x00, 0xe3, 0x1d, 0xfe, 0x85, 0x59, 0x9b, 0xcb, 0x5c, 0x2b, 0xbe, 0xcf,
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0x20, 0x1f, 0x5f, 0x49, 0xf1, 0xea, 0x31, 0x07, 0x7d, 0xa9, 0x26, 0xcb, 0x31, 0x03, 0x9d, 0x82,
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0x33, 0x2f, 0xed, 0x67, 0xa3, 0xa9, 0xb1, 0xc9, 0xe6, 0x34, 0x6c, 0xd7, 0xb5, 0x1a, 0x0a, 0x94,
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0x11, 0xa7, 0xd9, 0x26, 0xff, 0x0e, 0x8d, 0x72, 0xc1, 0x7b, 0x53, 0x9a, 0x13, 0x78, 0x7e, 0x16,
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0x38, 0x74, 0x7c, 0xb2, 0xdc, 0x60, 0x2c, 0x8c, 0xe8, 0x31, 0xf8, 0xd9, 0x7b, 0xac, 0xa6, 0x71,
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0xee, 0x61, 0x0c, 0x1a, 0xa4, 0x2f, 0x47, 0x2f, 0xe2, 0x22, 0xbd, 0x01, 0xe5, 0x25, 0xb6, 0x95,
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0xda, 0x3f, 0xf7, 0x03, 0xf4, 0x0e, 0xd6, 0x8c, 0xbb, 0x69, 0x1d, 0xcb, 0xd1, 0xe2, 0x60, 0xdb,
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0xf5, 0x0b, 0x85, 0x98, 0xe6, 0x17, 0xbe, 0x29, 0x4e, 0xa7, 0x90, 0x11, 0xac, 0xbc, 0xa5, 0x3e,
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0x05, 0xfe, 0xe9, 0x56, 0x93, 0x00, 0x00, 0x00, 0x01, 0x02
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};
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#endif
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static const uint8_t
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DiffieHellmanGroupExchangeRequest = 34,
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DiffieHellmanGroupExchangeGroup = 31,
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DiffieHellmanGroupExchangeInitialize = 32,
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DiffieHellmanGroupExchangeReply = 33;
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/*
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* XXX
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* Like a non-trivial amount of other code, this has been
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* written a bit fast-and-loose. The usage of the dh_ and
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* k_ in particularly are a bit dodgy and need to be freed
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* in the destructor.
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*
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* Need to add assertions and frees.
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*/
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template<CryptoHash::Algorithm hash_algorithm>
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class DiffieHellmanGroupExchange : public SSH::KeyExchange {
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LogHandle log_;
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SSH::Session *session_;
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DH *dh_;
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Buffer key_exchange_;
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BIGNUM *k_;
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public:
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DiffieHellmanGroupExchange(SSH::Session *session, const std::string& key_exchange_name)
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: SSH::KeyExchange(key_exchange_name),
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log_("/ssh/key_exchange/" + key_exchange_name),
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session_(session),
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dh_(NULL),
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key_exchange_(),
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k_()
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{ }
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~DiffieHellmanGroupExchange()
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{ }
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KeyExchange *clone(void) const
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{
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return (new DiffieHellmanGroupExchange(session_, name_));
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}
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bool hash(Buffer *out, const Buffer *in) const
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{
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return (CryptoHash::hash(hash_algorithm, out, in));
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}
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bool input(Filter* sender, Buffer *in)
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{
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SSH::ServerHostKey *key;
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uint32_t max, min, n;
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BIGNUM *e, *f;
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Buffer server_public_key;
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Buffer signature;
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Buffer packet;
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Buffer group;
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Buffer exchange_hash;
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Buffer data;
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Buffer initialize;
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switch (in->peek()) {
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case DiffieHellmanGroupExchangeRequest:
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if (session_->role_ != SSH::ServerRole) {
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ERROR(log_) << "Received group exchange request as client.";
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return (false);
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}
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in->skip(1);
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key_exchange_ = *in;
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if (!SSH::UInt32::decode(&min, in))
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return (false);
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if (!SSH::UInt32::decode(&n, in))
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return (false);
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if (!SSH::UInt32::decode(&max, in))
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return (false);
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if (min < DH_GROUP_MIN)
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min = DH_GROUP_MIN;
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if (max > DH_GROUP_MAX)
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max = DH_GROUP_MAX;
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if (min > max)
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return (false);
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if (n < min)
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n = min;
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else if (n > max)
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n = max;
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#ifdef USE_TEST_GROUP
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group.append(test_prime_and_generator, sizeof test_prime_and_generator);
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dh_ = DH_new();
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SSH::MPInt::decode(&dh_->p, &group);
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SSH::MPInt::decode(&dh_->g, &group);
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ASSERT(log_, group.empty());
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#else
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DEBUG(log_) << "Doing DH_generate_parameters for " << n << " bits.";
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ASSERT(log_, dh_ == NULL);
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dh_ = DH_generate_parameters(n, 2, NULL, NULL);
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if (dh_ == NULL) {
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ERROR(log_) << "DH_generate_parameters failed.";
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return (false);
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}
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#endif
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SSH::MPInt::encode(&group, dh_->p);
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SSH::MPInt::encode(&group, dh_->g);
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key_exchange_.append(group);
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packet.append(DiffieHellmanGroupExchangeGroup);
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packet.append(group);
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sender->produce(packet);
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return (true);
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case DiffieHellmanGroupExchangeGroup:
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if (session_->role_ != SSH::ClientRole) {
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ERROR(log_) << "Received DH group as server.";
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return (false);
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}
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in->skip(1);
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key_exchange_.append(in);
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dh_ = DH_new();
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if (dh_ == NULL) {
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ERROR(log_) << "DH_new failed.";
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return (false);
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}
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if (!SSH::MPInt::decode(&dh_->p, in))
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return (false);
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if (!SSH::MPInt::decode(&dh_->g, in))
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return (false);
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if (!DH_generate_key(dh_)) {
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ERROR(log_) << "DH_generate_key failed.";
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return (false);
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}
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e = dh_->pub_key;
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SSH::MPInt::encode(&initialize, e);
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key_exchange_.append(initialize);
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packet.append(DiffieHellmanGroupExchangeInitialize);
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packet.append(initialize);
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sender->produce(packet);
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return (true);
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case DiffieHellmanGroupExchangeInitialize:
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if (session_->role_ != SSH::ServerRole) {
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ERROR(log_) << "Received group exchange initialization as client.";
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return (false);
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}
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in->skip(1);
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key_exchange_.append(in);
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if (!SSH::MPInt::decode(&e, in))
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return (false);
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if (!DH_generate_key(dh_))
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return (false);
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f = dh_->pub_key;
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SSH::MPInt::encode(&key_exchange_, f);
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if (!exchange_finish(e)) {
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ERROR(log_) << "Server key exchange finish failed.";
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return (false);
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}
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key = session_->chosen_algorithms_.server_host_key_;
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if (!key->sign(&signature, &session_->exchange_hash_))
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return (false);
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key->encode_public_key(&server_public_key);
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packet.append(DiffieHellmanGroupExchangeReply);
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SSH::String::encode(&packet, server_public_key);
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SSH::MPInt::encode(&packet, f);
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SSH::String::encode(&packet, &signature);
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sender->produce(packet);
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sender->flush(SSH::ALGORITHM_NEGOTIATED);
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/*
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* XXX
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* Should send NEWKEYS.
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*/
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return (true);
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case DiffieHellmanGroupExchangeReply:
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if (session_->role_ != SSH::ClientRole) {
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ERROR(log_) << "Received group exchange reply as client.";
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return (false);
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}
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in->skip(1);
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if (!SSH::String::decode(&server_public_key, in))
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return (false);
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if (!SSH::MPInt::decode(&f, in))
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return (false);
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if (!SSH::String::decode(&signature, in))
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return (false);
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key = session_->chosen_algorithms_.server_host_key_;
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if (!key->decode_public_key(&server_public_key)) {
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ERROR(log_) << "Could not decode server public key:" << std::endl << server_public_key.hexdump();
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return (false);
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}
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SSH::MPInt::encode(&key_exchange_, f);
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if (!exchange_finish(f)) {
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ERROR(log_) << "Client key exchange finish failed.";
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return (false);
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}
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if (!key->verify(&signature, &session_->exchange_hash_)) {
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ERROR(log_) << "Failed to verify exchange hash.";
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return (false);
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}
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sender->flush(SSH::ALGORITHM_NEGOTIATED);
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/*
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* XXX
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* Should send NEWKEYS, but we're not ready for that yet.
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* For now we just assume the peer will do it. How lazy,
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* no?
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*/
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return (true);
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default:
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ERROR(log_) << "Not yet implemented.";
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return (false);
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}
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}
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bool init(Buffer *out)
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{
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ASSERT(log_, out->empty());
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ASSERT(log_, session_->role_ == SSH::ClientRole);
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Buffer request;
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SSH::UInt32::encode(&request, DH_GROUP_MIN);
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SSH::UInt32::encode(&request, DH_GROUP_MIN);
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SSH::UInt32::encode(&request, DH_GROUP_MAX);
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key_exchange_ = request;
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out->append(DiffieHellmanGroupExchangeRequest);
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out->append(request);
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return (true);
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}
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private:
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bool exchange_finish(BIGNUM *remote_pubkey)
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{
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SSH::ServerHostKey *key;
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Buffer server_public_key;
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Buffer exchange_hash;
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Buffer data;
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ASSERT(log_, dh_ != NULL);
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uint8_t secret[DH_size(dh_)];
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int secretlen = DH_compute_key(secret, remote_pubkey, dh_);
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if (secretlen == -1)
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return (false);
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k_ = BN_bin2bn(secret, secretlen, NULL);
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if (k_ == NULL)
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return (false);
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key = session_->chosen_algorithms_.server_host_key_;
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key->encode_public_key(&server_public_key);
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SSH::String::encode(&data, session_->client_version_);
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SSH::String::encode(&data, session_->server_version_);
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SSH::String::encode(&data, session_->client_kexinit_);
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SSH::String::encode(&data, session_->server_kexinit_);
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SSH::String::encode(&data, server_public_key);
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data.append(key_exchange_);
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SSH::MPInt::encode(&data, k_);
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if (!CryptoHash::hash(hash_algorithm, &exchange_hash, &data))
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return (false);
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session_->exchange_hash_ = exchange_hash;
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SSH::MPInt::encode(&session_->shared_secret_, k_);
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if (session_->session_id_.empty())
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session_->session_id_ = exchange_hash;
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return (true);
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}
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};
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}
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void
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SSH::KeyExchange::add_algorithms(SSH::Session *session)
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{
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session->algorithm_negotiation_->add_algorithm(new DiffieHellmanGroupExchange<CryptoHash::SHA256>(session, "diffie-hellman-group-exchange-sha256"));
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session->algorithm_negotiation_->add_algorithm(new DiffieHellmanGroupExchange<CryptoHash::SHA1>(session, "diffie-hellman-group-exchange-sha1"));
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}
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