cipher.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 cipher API defined in <openssl/evp.h> so
// that it can be used as part of the crypto layer of the OpenVPN core.
 
#ifndef OPENVPN_OPENSSL_CRYPTO_CIPHER_H
#define OPENVPN_OPENSSL_CRYPTO_CIPHER_H
 
#include <string>
 
#include <openssl/evp.h>
#include <openssl/objects.h>
#include <openssl/opensslv.h>
 
#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/crypto/static_key.hpp>
#include <openvpn/crypto/cryptoalgs.hpp>
#include <openvpn/openssl/util/error.hpp>
#include <openvpn/openssl/compat.hpp>
 
namespace openvpn::OpenSSLCrypto {
class CipherContext
{
    /* In OpenSSL 3.0 the method that returns EVP_CIPHER, the cipher needs to be
     * freed afterwards, thus needing a non-const type. In contrast, OpenSSL 1.1.1
     * and lower returns a const type, needing a const type */
#if OPENSSL_VERSION_NUMBER < 0x30000000L
    using evp_cipher_type = const EVP_CIPHER;
#else
    using evp_cipher_type = EVP_CIPHER;
#endif
 
    using CIPHER_unique_ptr = std::unique_ptr<evp_cipher_type, decltype(&::EVP_CIPHER_free)>;
 
    CipherContext(const CipherContext &) = delete;
    CipherContext &operator=(const CipherContext &) = delete;
 
  public:
    OPENVPN_SIMPLE_EXCEPTION(openssl_cipher_mode_error);
    OPENVPN_SIMPLE_EXCEPTION(openssl_cipher_uninitialized);
    OPENVPN_EXCEPTION(openssl_cipher_error);
 
    // mode parameter for constructor
    enum
    {
        MODE_UNDEF = -1,
        ENCRYPT = 1,
        DECRYPT = 0
    };
 
    // OpenSSL cipher constants
    enum
    {
        MAX_IV_LENGTH = EVP_MAX_IV_LENGTH,
        CIPH_CBC_MODE = EVP_CIPH_CBC_MODE
    };
 
    CipherContext() = default;
 
    ~CipherContext()
    {
        free_cipher_context();
    }
 
    static bool is_supported(SSLLib::Ctx libctx, const CryptoAlgs::Type alg)
    {
        CIPHER_unique_ptr cipher(cipher_type(libctx, alg), EVP_CIPHER_free);
        return (bool)(cipher);
    }
 
    void init(SSLLib::Ctx libctx, const CryptoAlgs::Type alg, const unsigned char *key, const int mode)
    {
        // check that mode is valid
        if (!(mode == ENCRYPT || mode == DECRYPT))
            throw openssl_cipher_mode_error();
        free_cipher_context();
        ctx = EVP_CIPHER_CTX_new();
        EVP_CIPHER_CTX_reset(ctx);
        CIPHER_unique_ptr cipher(cipher_type(libctx, alg), EVP_CIPHER_free);
 
        if (!cipher)
            OPENVPN_THROW(openssl_cipher_error, CryptoAlgs::name(alg) << ": not usable");
 
        if (!EVP_CipherInit_ex(ctx, cipher.get(), nullptr, key, nullptr, mode))
        {
            openssl_clear_error_stack();
            free_cipher_context();
            throw openssl_cipher_error("EVP_CipherInit_ex (init)");
        }
    }
 
    void reset(const unsigned char *iv)
    {
        check_initialized();
        if (!EVP_CipherInit_ex(ctx, nullptr, nullptr, nullptr, iv, -1))
        {
            openssl_clear_error_stack();
            throw openssl_cipher_error("EVP_CipherInit_ex (reset)");
        }
    }
 
    bool update(unsigned char *out,
                const size_t max_out_size,
                const unsigned char *in,
                const size_t in_size,
                size_t &out_acc)
    {
        check_initialized();
        int outlen;
        if (EVP_CipherUpdate(ctx, out, &outlen, in, int(in_size)))
        {
            out_acc += outlen;
            return true;
        }
 
        openssl_clear_error_stack();
        return false;
    }
 
    bool final(unsigned char *out, const size_t max_out_size, size_t &out_acc)
    {
        check_initialized();
        int outlen;
        if (EVP_CipherFinal_ex(ctx, out, &outlen))
        {
            out_acc += outlen;
            return true;
        }
 
        openssl_clear_error_stack();
        return false;
    }
 
    bool is_initialized() const
    {
        return ctx != nullptr;
    }
 
    size_t iv_length() const
    {
        check_initialized();
        return EVP_CIPHER_CTX_iv_length(ctx);
    }
 
    size_t block_size() const
    {
        check_initialized();
        return EVP_CIPHER_CTX_block_size(ctx);
    }
 
    // return cipher mode (such as CIPH_CBC_MODE, etc.)
    int cipher_mode() const
    {
        check_initialized();
        return EVP_CIPHER_CTX_mode(ctx);
    }
 
  private:
    static evp_cipher_type *cipher_type(SSLLib::Ctx libctx, const CryptoAlgs::Type alg)
    {
        switch (alg)
        {
        case CryptoAlgs::AES_128_CBC:
            return EVP_CIPHER_fetch(libctx, "AES-128-CBC", nullptr);
        case CryptoAlgs::AES_192_CBC:
            return EVP_CIPHER_fetch(libctx, "AES-192-CBC", nullptr);
        case CryptoAlgs::AES_256_CBC:
            return EVP_CIPHER_fetch(libctx, "AES-256-CBC", nullptr);
        case CryptoAlgs::AES_256_CTR:
            return EVP_CIPHER_fetch(libctx, "AES-256-CTR", nullptr);
        case CryptoAlgs::DES_CBC:
            return EVP_CIPHER_fetch(libctx, "DES-CBC", nullptr);
        case CryptoAlgs::DES_EDE3_CBC:
            return EVP_CIPHER_fetch(libctx, "DES-EDE-CBC", nullptr);
        case CryptoAlgs::BF_CBC:
            return EVP_CIPHER_fetch(libctx, "BF-CBC", nullptr);
        default:
            return nullptr;
        }
    }
 
    void free_cipher_context()
    {
        EVP_CIPHER_CTX_free(ctx);
        ctx = nullptr;
    }
 
    void check_initialized() const
    {
#ifdef OPENVPN_ENABLE_ASSERT
        if (ctx == nullptr)
            throw openssl_cipher_uninitialized();
#endif
    }
 
    EVP_CIPHER_CTX *ctx = nullptr;
};
} // namespace openvpn::OpenSSLCrypto
 
#endif