keymaster/km_openssl/block_cipher_operation.cpp

/*
 * Copyright 2014 The Android Open Source Project
 *
 * 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.
 */

#include "block_cipher_operation.h"

#include <utility>

#include <stdio.h>

#include <keymaster/UniquePtr.h>

#include <openssl/aes.h>
#include <openssl/err.h>
#include <openssl/rand.h>

#include <keymaster/logger.h>

#include <keymaster/km_openssl/aes_key.h>
#include <keymaster/km_openssl/openssl_err.h>
#include <keymaster/km_openssl/openssl_utils.h>

namespace keymaster {

static const size_t GCM_NONCE_SIZE = 12;

inline bool allows_padding(keymaster_block_mode_t block_mode) {
    switch (block_mode) {
    case KM_MODE_CTR:
    case KM_MODE_GCM:
        return false;
    case KM_MODE_ECB:
    case KM_MODE_CBC:
        return true;
    }
    assert(false /* Can't get here */);
    return false;
}

static keymaster_error_t GetAndValidateGcmTagLength(const AuthorizationSet& begin_params,
                                                    const AuthProxy& key_params,
                                                    size_t* tag_length) {
    uint32_t tag_length_bits;
    if (!begin_params.GetTagValue(TAG_MAC_LENGTH, &tag_length_bits)) {
        return KM_ERROR_MISSING_MAC_LENGTH;
    }

    uint32_t min_tag_length_bits;
    if (!key_params.GetTagValue(TAG_MIN_MAC_LENGTH, &min_tag_length_bits)) {
        LOG_E("AES GCM key must have KM_TAG_MIN_MAC_LENGTH");
        return KM_ERROR_INVALID_KEY_BLOB;
    }

    if (tag_length_bits % 8 != 0 || tag_length_bits > kMaxGcmTagLength ||
        tag_length_bits < kMinGcmTagLength) {
        return KM_ERROR_UNSUPPORTED_MAC_LENGTH;
    }

    if (tag_length_bits < min_tag_length_bits) {
        return KM_ERROR_INVALID_MAC_LENGTH;
    }

    *tag_length = tag_length_bits / 8;
    return KM_ERROR_OK;
}

OperationPtr BlockCipherOperationFactory::CreateOperation(Key&& key,
                                                          const AuthorizationSet& begin_params,
                                                          keymaster_error_t* error) {
    *error = KM_ERROR_OK;
    keymaster_block_mode_t block_mode;
    if (!begin_params.GetTagValue(TAG_BLOCK_MODE, &block_mode)) {
        LOG_E("%zu block modes specified in begin params",
              begin_params.GetTagCount(TAG_BLOCK_MODE));
        *error = KM_ERROR_UNSUPPORTED_BLOCK_MODE;
        return nullptr;
    } else if (!supported(block_mode)) {
        LOG_E("Block mode %d not supported", block_mode);
        *error = KM_ERROR_UNSUPPORTED_BLOCK_MODE;
        return nullptr;
    } else if (!key.authorizations().Contains(TAG_BLOCK_MODE, block_mode)) {
        LOG_E("Block mode %d was specified, but not authorized by key", block_mode);
        *error = KM_ERROR_INCOMPATIBLE_BLOCK_MODE;
        return nullptr;
    }

    size_t tag_length = 0;
    if (block_mode == KM_MODE_GCM) {
        *error = GetAndValidateGcmTagLength(begin_params, key.authorizations(), &tag_length);
        if (*error != KM_ERROR_OK) {
            return nullptr;
        }
    }

    keymaster_padding_t padding;
    if (!GetAndValidatePadding(begin_params, key, &padding, error)) {
        return nullptr;
    }
    if (!allows_padding(block_mode) && padding != KM_PAD_NONE) {
        LOG_E("Mode does not support padding");
        *error = KM_ERROR_INCOMPATIBLE_PADDING_MODE;
        return nullptr;
    }

    bool caller_nonce = key.authorizations().GetTagValue(TAG_CALLER_NONCE);

    OperationPtr op;
    switch (purpose_) {
    case KM_PURPOSE_ENCRYPT:
        op.reset(new (std::nothrow) BlockCipherEvpEncryptOperation(  //
            block_mode, padding, caller_nonce, tag_length, std::move(key),
            GetCipherDescription()));
        break;
    case KM_PURPOSE_DECRYPT:
        op.reset(new (std::nothrow) BlockCipherEvpDecryptOperation(
            block_mode, padding, tag_length, std::move(key), GetCipherDescription()));
        break;
    default:
        *error = KM_ERROR_UNSUPPORTED_PURPOSE;
        return nullptr;
    }

    if (!op) *error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
    return op;
}

static const keymaster_padding_t supported_padding_modes[] = {KM_PAD_NONE, KM_PAD_PKCS7};
const keymaster_padding_t*
BlockCipherOperationFactory::SupportedPaddingModes(size_t* padding_mode_count) const {
    *padding_mode_count = array_length(supported_padding_modes);
    return supported_padding_modes;
}

BlockCipherEvpOperation::BlockCipherEvpOperation(keymaster_purpose_t purpose,
                                                 keymaster_block_mode_t block_mode,
                                                 keymaster_padding_t padding, bool caller_iv,
                                                 size_t tag_length, Key&& key,
                                                 const EvpCipherDescription& cipher_description)
    : Operation(purpose, key.hw_enforced_move(), key.sw_enforced_move()), block_mode_(block_mode),
      caller_iv_(caller_iv), tag_length_(tag_length), data_started_(false), padding_(padding),
      key_(key.key_material_move()), cipher_description_(cipher_description) {
    EVP_CIPHER_CTX_init(&ctx_);
}

BlockCipherEvpOperation::~BlockCipherEvpOperation() {
    EVP_CIPHER_CTX_cleanup(&ctx_);
}

keymaster_error_t BlockCipherEvpOperation::Begin(const AuthorizationSet& /* input_params */,
                                                 AuthorizationSet* /* output_params */) {
    auto rc = GenerateRandom(reinterpret_cast<uint8_t*>(&operation_handle_),
                             (size_t)sizeof(operation_handle_));
    if (rc != KM_ERROR_OK) return rc;

    auto retval = InitializeCipher(key_);
    key_ = {};
    return retval;
}

keymaster_error_t BlockCipherEvpOperation::Update(const AuthorizationSet& additional_params,
                                                  const Buffer& input,
                                                  AuthorizationSet* /* output_params */,
                                                  Buffer* output, size_t* input_consumed) {
    keymaster_error_t error;
    if (block_mode_ == KM_MODE_GCM && !HandleAad(additional_params, input, &error)) return error;
    if (!InternalUpdate(input.peek_read(), input.available_read(), output, &error)) return error;
    *input_consumed = input.available_read();

    return KM_ERROR_OK;
}

// NOLINTNEXTLINE(google-runtime-int)
inline bool is_bad_decrypt(unsigned long error) {
    return (ERR_GET_LIB(error) == ERR_LIB_CIPHER &&  //
            ERR_GET_REASON(error) == CIPHER_R_BAD_DECRYPT);
}

keymaster_error_t BlockCipherEvpOperation::Finish(const AuthorizationSet& additional_params,
                                                  const Buffer& input,
                                                  const Buffer& /* signature */,
                                                  AuthorizationSet* output_params, Buffer* output) {
    keymaster_error_t error;
    if (!UpdateForFinish(additional_params, input, output_params, output, &error)) return error;
    if (!output->reserve(block_size_bytes())) return KM_ERROR_MEMORY_ALLOCATION_FAILED;

    if (block_mode_ == KM_MODE_GCM && aad_block_buf_len_ > 0 && !ProcessBufferedAadBlock(&error)) {
        return error;
    }

    int output_written = -1;
    if (!EVP_CipherFinal_ex(&ctx_, output->peek_write(), &output_written)) {
        if (tag_length_ > 0) return KM_ERROR_VERIFICATION_FAILED;
        char buf[128];
        ERR_error_string_n(ERR_peek_last_error(), buf, sizeof(buf));
        LOG_E("Error encrypting final block: %s", buf);
        return TranslateLastOpenSslError();
    }

    assert(output_written >= 0);
    assert(static_cast<size_t>(output_written) <= block_size_bytes());
    if (!output->advance_write(output_written)) return KM_ERROR_UNKNOWN_ERROR;
    return KM_ERROR_OK;
}

bool BlockCipherEvpOperation::need_iv() const {
    switch (block_mode_) {
    case KM_MODE_CBC:
    case KM_MODE_CTR:
    case KM_MODE_GCM:
        return true;
    case KM_MODE_ECB:
        return false;
    default:
        // Shouldn't get here.
        assert(false);
        return false;
    }
}

keymaster_error_t BlockCipherEvpOperation::InitializeCipher(const KeymasterKeyBlob& key) {
    keymaster_error_t error;
    const EVP_CIPHER* cipher =
        cipher_description_.GetCipherInstance(key.key_material_size, block_mode_, &error);
    if (error) return error;

    if (!EVP_CipherInit_ex(&ctx_, cipher, nullptr /* engine */, key.key_material, iv_.data,
                           evp_encrypt_mode())) {
        return TranslateLastOpenSslError();
    }

    switch (padding_) {
    case KM_PAD_NONE:
        EVP_CIPHER_CTX_set_padding(&ctx_, 0 /* disable padding */);
        break;
    case KM_PAD_PKCS7:
        // This is the default for OpenSSL EVP cipher operations.
        break;
    default:
        return KM_ERROR_UNSUPPORTED_PADDING_MODE;
    }

    if (block_mode_ == KM_MODE_GCM) {
        aad_block_buf_.reset(new (std::nothrow) uint8_t[block_size_bytes()]);
        if (!aad_block_buf_) return KM_ERROR_MEMORY_ALLOCATION_FAILED;
        aad_block_buf_len_ = 0;
    }

    return KM_ERROR_OK;
}

keymaster_error_t BlockCipherEvpOperation::GetIv(const AuthorizationSet& input_params) {
    keymaster_blob_t iv_blob;
    if (!input_params.GetTagValue(TAG_NONCE, &iv_blob)) {
        LOG_E("No IV provided");
        return KM_ERROR_INVALID_ARGUMENT;
    }

    if (block_mode_ != KM_MODE_GCM && iv_blob.data_length != block_size_bytes()) {
        LOG_E("Expected %zu-byte IV for operation, but got %zu bytes", block_size_bytes(),
              iv_blob.data_length);
        return KM_ERROR_INVALID_NONCE;
    }

    if (block_mode_ == KM_MODE_GCM && iv_blob.data_length != GCM_NONCE_SIZE) {
        LOG_E("Expected %zu-byte nonce for GCM operation, but got %zu bytes", GCM_NONCE_SIZE,
              iv_blob.data_length);
        return KM_ERROR_INVALID_NONCE;
    }

    iv_ = KeymasterBlob(iv_blob.data, iv_blob.data_length);
    if (!iv_.data) return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    return KM_ERROR_OK;
}

/*
 * Process Incoming Associated Authentication Data.
 *
 * This method is more complex than might be expected, because the underlying library silently does
 * the wrong thing when given partial AAD blocks, so we have to take care to process AAD in block
 * size increments, buffering (in aad_block_buf_) when given smaller amounts of data.
 */
bool BlockCipherEvpOperation::HandleAad(const AuthorizationSet& input_params, const Buffer& input,
                                        keymaster_error_t* error) {
    assert(tag_length_ > 0);
    assert(error);

    keymaster_blob_t aad;
    if (input_params.GetTagValue(TAG_ASSOCIATED_DATA, &aad)) {
        if (data_started_) {
            *error = KM_ERROR_INVALID_TAG;
            return false;
        }

        if (aad_block_buf_len_ > 0) {
            FillBufferedAadBlock(&aad);
            if (aad_block_buf_len_ == block_size_bytes() && !ProcessBufferedAadBlock(error))
                return false;
        }

        size_t block_size = block_size_bytes();
        size_t blocks_to_process = aad.data_length / block_size;
        if (blocks_to_process && !ProcessAadBlocks(aad.data, blocks_to_process, error))
            return false;
        aad.data += blocks_to_process * block_size;
        aad.data_length -= blocks_to_process * block_size;

        FillBufferedAadBlock(&aad);
        assert(aad.data_length == 0);
    }

    if (input.available_read()) {
        data_started_ = true;
        // Data has begun, no more AAD is allowed.  Process any buffered AAD.
        if (aad_block_buf_len_ > 0 && !ProcessBufferedAadBlock(error)) return false;
    }

    return true;
}

bool BlockCipherEvpOperation::ProcessBufferedAadBlock(keymaster_error_t* error) {
    int output_written;
    if (EVP_CipherUpdate(&ctx_, nullptr /* out */, &output_written, aad_block_buf_.get(),
                         aad_block_buf_len_)) {
        aad_block_buf_len_ = 0;
        return true;
    }
    *error = TranslateLastOpenSslError();
    return false;
}

bool BlockCipherEvpOperation::ProcessAadBlocks(const uint8_t* data, size_t blocks,
                                               keymaster_error_t* error) {
    int output_written;
    if (EVP_CipherUpdate(&ctx_, nullptr /* out */, &output_written, data,
                         blocks * block_size_bytes())) {
        return true;
    }
    *error = TranslateLastOpenSslError();
    return false;
}

inline size_t min(size_t a, size_t b) {
    return (a < b) ? a : b;
}

void BlockCipherEvpOperation::FillBufferedAadBlock(keymaster_blob_t* aad) {
    size_t to_buffer = min(block_size_bytes() - aad_block_buf_len_, aad->data_length);
    memcpy(aad_block_buf_.get() + aad_block_buf_len_, aad->data, to_buffer);
    aad->data += to_buffer;
    aad->data_length -= to_buffer;
    aad_block_buf_len_ += to_buffer;
}

bool BlockCipherEvpOperation::InternalUpdate(const uint8_t* input, size_t input_length,
                                             Buffer* output, keymaster_error_t* error) {
    assert(output);
    assert(error);

    if (!input_length) return true;

    if (!output->reserve(input_length + block_size_bytes())) {
        *error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
        return false;
    }

    int output_written = -1;
    if (!EVP_CipherUpdate(&ctx_, output->peek_write(), &output_written, input, input_length)) {
        *error = TranslateLastOpenSslError();
        return false;
    }
    return output->advance_write(output_written);
}

bool BlockCipherEvpOperation::UpdateForFinish(const AuthorizationSet& additional_params,
                                              const Buffer& input, AuthorizationSet* output_params,
                                              Buffer* output, keymaster_error_t* error) {
    if (input.available_read() || !additional_params.empty()) {
        size_t input_consumed;
        *error = Update(additional_params, input, output_params, output, &input_consumed);
        if (*error != KM_ERROR_OK) return false;
        if (input_consumed != input.available_read()) {
            *error = KM_ERROR_INVALID_INPUT_LENGTH;
            return false;
        }
    }

    return true;
}

keymaster_error_t BlockCipherEvpEncryptOperation::Begin(const AuthorizationSet& input_params,
                                                        AuthorizationSet* output_params) {
    if (!output_params) return KM_ERROR_OUTPUT_PARAMETER_NULL;

    if (need_iv()) {
        keymaster_error_t error = KM_ERROR_OK;
        if (input_params.find(TAG_NONCE) == -1) {
            error = GenerateIv();
        } else if (caller_iv_) {
            error = GetIv(input_params);
        } else {
            error = KM_ERROR_CALLER_NONCE_PROHIBITED;
        }

        if (error != KM_ERROR_OK) return error;
        output_params->push_back(TAG_NONCE, iv_.data, iv_.data_length);
    }

    return BlockCipherEvpOperation::Begin(input_params, output_params);
}

keymaster_error_t BlockCipherEvpEncryptOperation::Finish(const AuthorizationSet& additional_params,
                                                         const Buffer& input,
                                                         const Buffer& signature,
                                                         AuthorizationSet* output_params,
                                                         Buffer* output) {
    if (!output->reserve(input.available_read() + block_size_bytes() + tag_length_)) {
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    }

    keymaster_error_t error =
        BlockCipherEvpOperation::Finish(additional_params, input, signature, output_params, output);
    if (error != KM_ERROR_OK) return error;

    if (tag_length_ > 0) {
        if (!output->reserve(tag_length_)) return KM_ERROR_MEMORY_ALLOCATION_FAILED;

        if (!EVP_CIPHER_CTX_ctrl(&ctx_, EVP_CTRL_GCM_GET_TAG, tag_length_, output->peek_write()))
            return TranslateLastOpenSslError();
        if (!output->advance_write(tag_length_)) return KM_ERROR_UNKNOWN_ERROR;
    }

    return KM_ERROR_OK;
}

keymaster_error_t BlockCipherEvpEncryptOperation::GenerateIv() {
    iv_.Reset((block_mode_ == KM_MODE_GCM) ? GCM_NONCE_SIZE : block_size_bytes());
    if (!iv_.data) return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    if (RAND_bytes(iv_.writable_data(), iv_.data_length) != 1) return TranslateLastOpenSslError();
    return KM_ERROR_OK;
}

keymaster_error_t BlockCipherEvpDecryptOperation::Begin(const AuthorizationSet& input_params,
                                                        AuthorizationSet* output_params) {
    if (need_iv()) {
        keymaster_error_t error = GetIv(input_params);
        if (error != KM_ERROR_OK) return error;
    }

    if (tag_length_ > 0) {
        tag_buf_.reset(new (std::nothrow) uint8_t[tag_length_]);
        if (!tag_buf_) return KM_ERROR_MEMORY_ALLOCATION_FAILED;
        tag_buf_len_ = 0;
    }

    return BlockCipherEvpOperation::Begin(input_params, output_params);
}

keymaster_error_t BlockCipherEvpDecryptOperation::Update(const AuthorizationSet& additional_params,
                                                         const Buffer& input,
                                                         AuthorizationSet* /* output_params */,
                                                         Buffer* output, size_t* input_consumed) {
    if (!output || !input_consumed) return KM_ERROR_OUTPUT_PARAMETER_NULL;

    // Barring error, we'll consume it all.
    *input_consumed = input.available_read();

    keymaster_error_t error;
    if (block_mode_ == KM_MODE_GCM) {
        if (!HandleAad(additional_params, input, &error)) return error;
        return ProcessAllButTagLengthBytes(input, output);
    }

    if (!InternalUpdate(input.peek_read(), input.available_read(), output, &error)) return error;
    return KM_ERROR_OK;
}

keymaster_error_t BlockCipherEvpDecryptOperation::ProcessAllButTagLengthBytes(const Buffer& input,
                                                                              Buffer* output) {
    if (input.available_read() <= tag_buf_unused()) {
        BufferCandidateTagData(input.peek_read(), input.available_read());
        return KM_ERROR_OK;
    }

    const size_t data_available = tag_buf_len_ + input.available_read();

    const size_t to_process = data_available - tag_length_;
    const size_t to_process_from_tag_buf = min(to_process, tag_buf_len_);
    const size_t to_process_from_input = to_process - to_process_from_tag_buf;

    if (!output->reserve(to_process + block_size_bytes())) return KM_ERROR_MEMORY_ALLOCATION_FAILED;

    keymaster_error_t error;
    if (!ProcessTagBufContentsAsData(to_process_from_tag_buf, output, &error)) return error;

    if (!InternalUpdate(input.peek_read(), to_process_from_input, output, &error)) return error;

    BufferCandidateTagData(input.peek_read() + to_process_from_input,
                           input.available_read() - to_process_from_input);
    assert(tag_buf_unused() == 0);

    return KM_ERROR_OK;
}

bool BlockCipherEvpDecryptOperation::ProcessTagBufContentsAsData(size_t to_process, Buffer* output,
                                                                 keymaster_error_t* error) {
    assert(to_process <= tag_buf_len_);
    if (!InternalUpdate(tag_buf_.get(), to_process, output, error)) return false;
    if (to_process < tag_buf_len_) {
        memmove(tag_buf_.get(), tag_buf_.get() + to_process, tag_buf_len_ - to_process);
    }
    tag_buf_len_ -= to_process;
    return true;
}

void BlockCipherEvpDecryptOperation::BufferCandidateTagData(const uint8_t* data,
                                                            size_t data_length) {
    assert(data_length <= tag_length_ - tag_buf_len_);
    memcpy(tag_buf_.get() + tag_buf_len_, data, data_length);
    tag_buf_len_ += data_length;
}

keymaster_error_t BlockCipherEvpDecryptOperation::Finish(const AuthorizationSet& additional_params,
                                                         const Buffer& input,
                                                         const Buffer& signature,
                                                         AuthorizationSet* output_params,
                                                         Buffer* output) {
    keymaster_error_t error;
    if (!UpdateForFinish(additional_params, input, output_params, output, &error)) return error;

    if (tag_buf_len_ < tag_length_) {
        return KM_ERROR_INVALID_INPUT_LENGTH;
    } else if (tag_length_ > 0 &&
               !EVP_CIPHER_CTX_ctrl(&ctx_, EVP_CTRL_GCM_SET_TAG, tag_length_, tag_buf_.get())) {
        return TranslateLastOpenSslError();
    }

    AuthorizationSet empty_params;
    Buffer empty_input;
    return BlockCipherEvpOperation::Finish(empty_params, empty_input, signature, output_params,
                                           output);
}

keymaster_error_t BlockCipherEvpOperation::Abort() {
    return KM_ERROR_OK;
}

}  // namespace keymaster