rsa_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 <openssl/rsa.h>
#include <openssl/evp.h>

#include "rsa_operation.h"

namespace keymaster {

struct EVP_PKEY_Delete {
    void operator()(EVP_PKEY* p) const { EVP_PKEY_free(p); }
};
struct BIGNUM_Delete {
    void operator()(BIGNUM* p) const { BN_free(p); }
};

struct RSA_Delete {
    void operator()(RSA* p) const { RSA_free(p); }
};

/**
 * Many OpenSSL APIs take ownership of an argument on success but don't free the argument on
 * failure. This means we need to tell our scoped pointers when we've transferred ownership, without
 * triggering a warning by not using the result of release().
 */
template <typename T, typename Delete_T>
inline void release_because_ownership_transferred(UniquePtr<T, Delete_T>& p) {
    T* val __attribute__((unused)) = p.release();
}

/* static */
keymaster_error_t RsaOperation::Generate(uint64_t public_exponent, uint32_t key_size,
                                         UniquePtr<uint8_t[]>* key_data, size_t* key_data_size) {
    if (key_data == NULL || key_data_size == NULL)
        return KM_ERROR_OUTPUT_PARAMETER_NULL;

    UniquePtr<BIGNUM, BIGNUM_Delete> exponent(BN_new());
    UniquePtr<RSA, RSA_Delete> rsa_key(RSA_new());
    UniquePtr<EVP_PKEY, EVP_PKEY_Delete> pkey(EVP_PKEY_new());
    if (rsa_key.get() == NULL || pkey.get() == NULL)
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;

    if (!BN_set_word(exponent.get(), public_exponent) ||
        !RSA_generate_key_ex(rsa_key.get(), key_size, exponent.get(), NULL /* callback */))
        return KM_ERROR_UNKNOWN_ERROR;

    if (!EVP_PKEY_assign_RSA(pkey.get(), rsa_key.get()))
        return KM_ERROR_UNKNOWN_ERROR;
    else
        release_because_ownership_transferred(rsa_key);

    *key_data_size = i2d_PrivateKey(pkey.get(), NULL);
    if (*key_data_size <= 0)
        return KM_ERROR_UNKNOWN_ERROR;

    key_data->reset(new uint8_t[*key_data_size]);
    if (key_data->get() == NULL)
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;

    uint8_t* tmp = key_data->get();
    i2d_PrivateKey(pkey.get(), &tmp);

    return KM_ERROR_OK;
}

RsaOperation::RsaOperation(keymaster_purpose_t purpose, const KeyBlob& key)
    : Operation(purpose), rsa_key_(NULL) {
    assert(key.algorithm() == KM_ALGORITHM_RSA);

    if ((!key.enforced().GetTagValue(TAG_DIGEST, &digest_) &&
         !key.unenforced().GetTagValue(TAG_DIGEST, &digest_)) ||
        digest_ != KM_DIGEST_NONE) {
        error_ = KM_ERROR_UNSUPPORTED_DIGEST;
        return;
    }

    if ((!key.enforced().GetTagValue(TAG_PADDING, &padding_) &&
         !key.unenforced().GetTagValue(TAG_PADDING, &padding_)) ||
        padding_ != KM_PAD_NONE) {
        error_ = KM_ERROR_UNSUPPORTED_PADDING_MODE;
        return;
    }

    UniquePtr<EVP_PKEY, EVP_PKEY_Delete> evp_key(EVP_PKEY_new());
    if (evp_key.get() == NULL) {
        error_ = KM_ERROR_MEMORY_ALLOCATION_FAILED;
        return;
    }

    EVP_PKEY* tmp_pkey = evp_key.get();
    const uint8_t* key_material = key.key_material();
    if (d2i_PrivateKey(EVP_PKEY_RSA, &tmp_pkey, &key_material, key.key_material_length()) == NULL) {
        error_ = KM_ERROR_INVALID_KEY_BLOB;
        return;
    }

    rsa_key_ = EVP_PKEY_get1_RSA(evp_key.get());
    if (rsa_key_ == NULL) {
        error_ = KM_ERROR_UNKNOWN_ERROR;
        return;
    }

    // Since we're not using a digest function, we just need to store the text, up to the key
    // size, until Finish is called, so we allocate a place to put it.
    if (!data_.Reinitialize(RSA_size(rsa_key_))) {
        error_ = KM_ERROR_MEMORY_ALLOCATION_FAILED;
        return;
    }
    error_ = KM_ERROR_OK;
}

RsaOperation::~RsaOperation() {
    if (rsa_key_ != NULL)
        RSA_free(rsa_key_);
}

keymaster_error_t RsaOperation::Update(const Buffer& input, Buffer* /* output */) {
    switch (purpose()) {
    default:
        return KM_ERROR_UNIMPLEMENTED;
    case KM_PURPOSE_SIGN:
    case KM_PURPOSE_VERIFY:
        return StoreData(input);
    }
}

keymaster_error_t RsaOperation::StoreData(const Buffer& input) {
    if (!data_.write(input.peek_read(), input.available_read()))
        return KM_ERROR_INVALID_INPUT_LENGTH;
    return KM_ERROR_OK;
}

keymaster_error_t RsaOperation::Finish(const Buffer& signature, Buffer* output) {
    switch (purpose()) {
    case KM_PURPOSE_SIGN: {
        output->Reinitialize(RSA_size(rsa_key_));
        if (data_.available_read() != output->buffer_size())
            return KM_ERROR_INVALID_INPUT_LENGTH;

        int bytes_encrypted = RSA_private_encrypt(data_.available_read(), data_.peek_read(),
                                                  output->peek_write(), rsa_key_, RSA_NO_PADDING);
        if (bytes_encrypted < 0)
            return KM_ERROR_UNKNOWN_ERROR;
        assert(bytes_encrypted == RSA_size(rsa_key_));
        output->advance_write(bytes_encrypted);
        return KM_ERROR_OK;
    }
    case KM_PURPOSE_VERIFY: {
        if ((int)data_.available_read() != RSA_size(rsa_key_))
            return KM_ERROR_INVALID_INPUT_LENGTH;
        if (data_.available_read() != signature.available_read())
            return KM_ERROR_VERIFICATION_FAILED;

        UniquePtr<uint8_t[]> decrypted_data(new uint8_t[RSA_size(rsa_key_)]);
        int bytes_decrypted = RSA_public_decrypt(signature.available_read(), signature.peek_read(),
                                                 decrypted_data.get(), rsa_key_, RSA_NO_PADDING);
        if (bytes_decrypted < 0)
            return KM_ERROR_UNKNOWN_ERROR;
        assert(bytes_decrypted == RSA_size(rsa_key_));

        if (memcmp_s(decrypted_data.get(), data_.peek_read(), data_.available_read()) == 0)
            return KM_ERROR_OK;
        return KM_ERROR_VERIFICATION_FAILED;
    }
    default:
        return KM_ERROR_UNIMPLEMENTED;
    }
}

}  // namespace keymaster