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/*
*
* Copyright (c) 2020-2021 Project CHIP Authors
* All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* @file
* This file implements the CHIP Secure Session object.
*
*/
#include <crypto/CHIPCryptoPAL.h>
#include <lib/core/CHIPEncoding.h>
#include <lib/support/BufferWriter.h>
#include <lib/support/CodeUtils.h>
#include <transport/CryptoContext.h>
#include <transport/raw/MessageHeader.h>
#include <lib/support/BytesToHex.h>
#include <string.h>
namespace chip {
namespace {
constexpr size_t kMaxAADLen = 128;
/* Session Establish Key Info */
constexpr uint8_t SEKeysInfo[] = { 0x53, 0x65, 0x73, 0x73, 0x69, 0x6f, 0x6e, 0x4b, 0x65, 0x79, 0x73 };
/* Session Resumption Key Info */
constexpr uint8_t RSEKeysInfo[] = { 0x53, 0x65, 0x73, 0x73, 0x69, 0x6f, 0x6e, 0x52, 0x65, 0x73, 0x75,
0x6d, 0x70, 0x74, 0x69, 0x6f, 0x6e, 0x4b, 0x65, 0x79, 0x73 };
} // namespace
using namespace Crypto;
#ifdef ENABLE_HSM_HKDF
using HKDF_sha_crypto = HKDF_shaHSM;
#else
using HKDF_sha_crypto = HKDF_sha;
#endif
CryptoContext::CryptoContext() : mKeyAvailable(false) {}
CryptoContext::~CryptoContext()
{
for (auto & key : mKeys)
{
ClearSecretData(key, sizeof(CryptoKey));
}
mKeyContext = nullptr;
}
CHIP_ERROR CryptoContext::InitFromSecret(const ByteSpan & secret, const ByteSpan & salt, SessionInfoType infoType, SessionRole role)
{
HKDF_sha_crypto mHKDF;
VerifyOrReturnError(mKeyAvailable == false, CHIP_ERROR_INCORRECT_STATE);
VerifyOrReturnError(secret.data() != nullptr, CHIP_ERROR_INVALID_ARGUMENT);
VerifyOrReturnError(secret.size() > 0, CHIP_ERROR_INVALID_ARGUMENT);
VerifyOrReturnError((salt.size() == 0) || (salt.data() != nullptr), CHIP_ERROR_INVALID_ARGUMENT);
const uint8_t * info = SEKeysInfo;
size_t infoLen = sizeof(SEKeysInfo);
if (infoType == SessionInfoType::kSessionResumption)
{
info = RSEKeysInfo;
infoLen = sizeof(RSEKeysInfo);
}
#if CHIP_CONFIG_SECURITY_TEST_MODE
// If enabled, override the generated session key with a known key pair
// to allow man-in-the-middle session key recovery for testing purposes.
#define TEST_SECRET_SIZE 32
constexpr uint8_t kTestSharedSecret[TEST_SECRET_SIZE] = CHIP_CONFIG_TEST_SHARED_SECRET_VALUE;
static_assert(sizeof(CHIP_CONFIG_TEST_SHARED_SECRET_VALUE) == TEST_SECRET_SIZE,
"CHIP_CONFIG_TEST_SHARED_SECRET_VALUE must be 32 bytes");
const ByteSpan & testSalt = ByteSpan(nullptr, 0);
(void) info;
(void) infoLen;
#warning \
"Warning: CONFIG_SECURITY_TEST_MODE=1 bypassing key negotiation... All sessions will use known, fixed test key, and NodeID=0 in NONCE. Node can only communicate with other nodes built with this flag set. Requires build flag 'treat_warnings_as_errors=false'."
ChipLogError(SecureChannel,
"Warning: CONFIG_SECURITY_TEST_MODE=1 bypassing key negotiation... All sessions will use known, fixed test key, "
"and NodeID=0 in NONCE. "
"Node can only communicate with other nodes built with this flag set.");
ReturnErrorOnFailure(mHKDF.HKDF_SHA256(kTestSharedSecret, TEST_SECRET_SIZE, testSalt.data(), testSalt.size(), SEKeysInfo,
sizeof(SEKeysInfo), &mKeys[0][0], sizeof(mKeys)));
#else
ReturnErrorOnFailure(
mHKDF.HKDF_SHA256(secret.data(), secret.size(), salt.data(), salt.size(), info, infoLen, &mKeys[0][0], sizeof(mKeys)));
#endif
mKeyAvailable = true;
mSessionRole = role;
return CHIP_NO_ERROR;
}
CHIP_ERROR CryptoContext::InitFromKeyPair(const Crypto::P256Keypair & local_keypair,
const Crypto::P256PublicKey & remote_public_key, const ByteSpan & salt,
SessionInfoType infoType, SessionRole role)
{
VerifyOrReturnError(mKeyAvailable == false, CHIP_ERROR_INCORRECT_STATE);
P256ECDHDerivedSecret secret;
ReturnErrorOnFailure(local_keypair.ECDH_derive_secret(remote_public_key, secret));
return InitFromSecret(ByteSpan(secret, secret.Length()), salt, infoType, role);
}
CHIP_ERROR CryptoContext::BuildNonce(NonceView nonce, uint8_t securityFlags, uint32_t messageCounter, NodeId nodeId)
{
Encoding::LittleEndian::BufferWriter bbuf(nonce.data(), nonce.size());
bbuf.Put8(securityFlags);
bbuf.Put32(messageCounter);
#if CHIP_CONFIG_SECURITY_TEST_MODE
bbuf.Put64(0); // Simplifies decryption of CASE sessions when in TEST_MODE.
#else
bbuf.Put64(nodeId);
#endif
return bbuf.Fit() ? CHIP_NO_ERROR : CHIP_ERROR_NO_MEMORY;
}
CHIP_ERROR CryptoContext::GetAdditionalAuthData(const PacketHeader & header, uint8_t * aad, uint16_t & len)
{
VerifyOrReturnError(len >= header.EncodeSizeBytes(), CHIP_ERROR_INVALID_ARGUMENT);
// Use unencrypted part of header as AAD. This will help
// integrity protect the whole message
uint16_t actualEncodedHeaderSize;
ReturnErrorOnFailure(header.Encode(aad, len, &actualEncodedHeaderSize));
VerifyOrReturnError(len >= actualEncodedHeaderSize, CHIP_ERROR_INVALID_ARGUMENT);
len = actualEncodedHeaderSize;
return CHIP_NO_ERROR;
}
CHIP_ERROR CryptoContext::Encrypt(const uint8_t * input, size_t input_length, uint8_t * output, ConstNonceView nonce,
PacketHeader & header, MessageAuthenticationCode & mac) const
{
const size_t taglen = header.MICTagLength();
VerifyOrDie(taglen <= kMaxTagLen);
VerifyOrReturnError(input != nullptr, CHIP_ERROR_INVALID_ARGUMENT);
VerifyOrReturnError(input_length > 0, CHIP_ERROR_INVALID_ARGUMENT);
VerifyOrReturnError(output != nullptr, CHIP_ERROR_INVALID_ARGUMENT);
uint8_t AAD[kMaxAADLen];
uint16_t aadLen = sizeof(AAD);
uint8_t tag[kMaxTagLen];
ReturnErrorOnFailure(GetAdditionalAuthData(header, AAD, aadLen));
if (mKeyContext)
{
ByteSpan plaintext(input, input_length);
MutableByteSpan ciphertext(output, input_length);
MutableByteSpan mic(tag, taglen);
ReturnErrorOnFailure(mKeyContext->EncryptMessage(plaintext, ByteSpan(AAD, aadLen), nonce, mic, ciphertext));
}
else
{
VerifyOrReturnError(mKeyAvailable, CHIP_ERROR_INVALID_USE_OF_SESSION_KEY);
KeyUsage usage = kR2IKey;
// Message is encrypted before sending. If the secure session was created by session
// initiator, we'll use I2R key to encrypt the message that's being transmitted.
// Otherwise, we'll use R2I key, as the responder is sending the message.
if (mSessionRole == SessionRole::kInitiator)
{
usage = kI2RKey;
}
ReturnErrorOnFailure(AES_CCM_encrypt(input, input_length, AAD, aadLen, mKeys[usage], Crypto::kAES_CCM128_Key_Length,
nonce.data(), nonce.size(), output, tag, taglen));
}
mac.SetTag(&header, tag, taglen);
return CHIP_NO_ERROR;
}
CHIP_ERROR CryptoContext::Decrypt(const uint8_t * input, size_t input_length, uint8_t * output, ConstNonceView nonce,
const PacketHeader & header, const MessageAuthenticationCode & mac) const
{
const size_t taglen = header.MICTagLength();
const uint8_t * tag = mac.GetTag();
uint8_t AAD[kMaxAADLen];
uint16_t aadLen = sizeof(AAD);
VerifyOrReturnError(input != nullptr, CHIP_ERROR_INVALID_ARGUMENT);
VerifyOrReturnError(input_length > 0, CHIP_ERROR_INVALID_ARGUMENT);
VerifyOrReturnError(output != nullptr, CHIP_ERROR_INVALID_ARGUMENT);
ReturnErrorOnFailure(GetAdditionalAuthData(header, AAD, aadLen));
if (nullptr != mKeyContext)
{
ByteSpan ciphertext(input, input_length);
MutableByteSpan plaintext(output, input_length);
ByteSpan mic(tag, taglen);
CHIP_ERROR err = mKeyContext->DecryptMessage(ciphertext, ByteSpan(AAD, aadLen), nonce, mic, plaintext);
ReturnErrorOnFailure(err);
}
else
{
VerifyOrReturnError(mKeyAvailable, CHIP_ERROR_INVALID_USE_OF_SESSION_KEY);
KeyUsage usage = kI2RKey;
// Message is decrypted on receive. If the secure session was created by session
// initiator, we'll use R2I key to decrypt the message (as it was sent by responder).
// Otherwise, we'll use I2R key, as the responder is sending the message.
if (mSessionRole == SessionRole::kInitiator)
{
usage = kR2IKey;
}
ReturnErrorOnFailure(AES_CCM_decrypt(input, input_length, AAD, aadLen, tag, taglen, mKeys[usage],
Crypto::kAES_CCM128_Key_Length, nonce.data(), nonce.size(), output));
}
return CHIP_NO_ERROR;
}
} // namespace chip