mac.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
//
 
// Wrap the OpenSSL HMAC API defined in <openssl/hmac.h> so
// that it can be used as part of the crypto layer of the OpenVPN core.
 
#pragma once
 
#include <string>
 
#include <openssl/opensslv.h>
/* The HMAC_* methods are deprecated in OpenSSL 3.0 and the EVP_MAC methods
 * do no exist in OpenSSL 1.1 yet. So use two distinct implementations */
#if OPENSSL_VERSION_NUMBER < 0x30000000L
#include <openvpn/openssl/crypto/hmac-compat.hpp>
#else
 
#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/openssl/crypto/digest.hpp>
 
#include <openssl/params.h>
 
 
namespace openvpn::OpenSSLCrypto {
class HMACContext
{
    HMACContext(const HMACContext &) = delete;
    HMACContext &operator=(const HMACContext &) = delete;
 
  public:
    HMACContext &operator=(HMACContext &&rhs)
    {
        erase();
        ctx = rhs.ctx;
        rhs.ctx = nullptr;
        return *this;
    }
 
    OPENVPN_SIMPLE_EXCEPTION(openssl_mac_uninitialized);
    OPENVPN_EXCEPTION(openssl_mac_error);
 
    enum
    {
        MAX_HMAC_SIZE = EVP_MAX_MD_SIZE
    };
 
    HMACContext() = default;
 
    HMACContext(const CryptoAlgs::Type digest, const unsigned char *key, const size_t key_size)
    {
        init(digest, key, key_size);
    }
 
    ~HMACContext()
    {
        erase();
    }
 
    void init(const CryptoAlgs::Type digest, const unsigned char *key, const size_t key_size)
    {
        erase();
        EVP_MAC *hmac = EVP_MAC_fetch(NULL, "HMAC", NULL);
        ctx = EVP_MAC_CTX_new(hmac);
        EVP_MAC_free(hmac);
 
        /* Save key since the caller might clear it */
        std::memcpy(this->key, key, key_size);
 
        /* Lookup/setting of parameters in OpenSSL 3.0 are string based */
        /* The OSSL_PARAM_construct_utf8_string needs a non const str even
         * though it does not modify the string */
        params[0] = OSSL_PARAM_construct_utf8_string("digest", const_cast<char *>(CryptoAlgs::name(digest)), 0);
        params[1] = OSSL_PARAM_construct_octet_string("key", this->key, key_size);
        params[2] = OSSL_PARAM_construct_end();
 
        if (!EVP_MAC_init(ctx, NULL, 0, params))
        {
            openssl_clear_error_stack();
            EVP_MAC_CTX_free(ctx);
            ctx = nullptr;
            throw openssl_mac_error("EVP_MAC_init (init)");
        }
    }
 
    void reset()
    {
        check_initialized();
        if (!EVP_MAC_init(ctx, nullptr, 0, params))
        {
            openssl_clear_error_stack();
            throw openssl_mac_error("EVP_HMAC_Init (reset)");
        }
    }
 
 
    void update(const unsigned char *in, const size_t size)
    {
        check_initialized();
 
        if (!EVP_MAC_update(ctx, in, size))
        {
            openssl_clear_error_stack();
            throw openssl_mac_error("EVP_MAC_Update");
        }
    }
 
    /* TODO: This function currently assumes that out has a length of MAX_HMAC_SIZE */
    size_t final(unsigned char *out)
    {
        check_initialized();
        size_t outlen;
        if (!EVP_MAC_final(ctx, out, &outlen, MAX_HMAC_SIZE))
        {
            openssl_clear_error_stack();
            throw openssl_mac_error("HMAC_Final");
        }
        return outlen;
    }
 
    size_t size() const
    {
        check_initialized();
        return size_();
    }
 
    bool is_initialized() const
    {
        return ctx != nullptr;
    }
 
  private:
    void erase()
    {
        EVP_MAC_CTX_free(ctx);
        ctx = nullptr;
    }
 
    size_t size_() const
    {
        return EVP_MAC_CTX_get_mac_size(ctx);
    }
 
    void check_initialized() const
    {
#ifdef OPENVPN_ENABLE_ASSERT
        if (!ctx)
            throw openssl_mac_uninitialized();
#endif
    }
 
    OSSL_PARAM params[3];
    uint8_t key[EVP_MAX_MD_SIZE];
    EVP_MAC_CTX *ctx = nullptr;
};
} // namespace openvpn::OpenSSLCrypto
 
#endif