# example_evp_cipher.c

This is an example how to use EVP_CipherInit_ex(), EVP_CipherUpdate() and EVP_CipherFinal_ex().

    /*
     * Copyright (c) 2008 Kungliga Tekniska Högskolan
     * (Royal Institute of Technology, Stockholm, Sweden).
     * All rights reserved.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     *
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     *
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * 3. Neither the name of the Institute nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */

    #include <krb5-types.h> /* should really be stdint.h */
    #include <hcrypto/evp.h>

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <err.h>
    #include <assert.h>

    #include "roken.h"

    /* key and initial vector */
    static char key[16] =
        "\xaa\xbb\x45\xd4\xaa\xbb\x45\xd4"
        "\xaa\xbb\x45\xd4\xaa\xbb\x45\xd4";
    static char ivec[16] =
        "\xaa\xbb\x45\xd4\xaa\xbb\x45\xd4"
        "\xaa\xbb\x45\xd4\xaa\xbb\x45\xd4";

    static void
    usage(int exit_code) __attribute__((noreturn));

    static void
    usage(int exit_code)
    {
        printf("usage: %s in out\n", getprogname());
        exit(exit_code);
    }

    int
    main(int argc, char **argv)
    {
        int encryptp = 1;
        const char *ifn = NULL, *ofn = NULL;
        FILE *in, *out;
        void *ibuf, *obuf;
        int ilen, olen;
        size_t block_size = 0;
        const EVP_CIPHER *c = EVP_aes_128_cbc();
        EVP_CIPHER_CTX ctx;
        int ret;

        setprogname(argv[0]);

        if (argc == 2) {
            if (strcmp(argv[1], "--version") == 0) {
                printf("version");
                exit(0);
            }
            if (strcmp(argv[1], "--help") == 0)
                usage(0);
            usage(1);
        } else if (argc == 4) {
            block_size = atoi(argv[1]);
            if (block_size == 0)
                errx(1, "invalid blocksize %s", argv[1]);
            ifn = argv[2];
            ofn = argv[3];
        } else
            usage(1);

        in = fopen(ifn, "r");
        if (in == NULL)
            errx(1, "failed to open input file");
        out = fopen(ofn, "w+");
        if (out == NULL)
            errx(1, "failed to open output file");

        /* Check that key and ivec are long enough */
        assert(EVP_CIPHER_key_length(c) <= sizeof(key));
        assert(EVP_CIPHER_iv_length(c) <= sizeof(ivec));

        /*
         * Allocate buffer, the output buffer is at least
         * EVP_CIPHER_block_size() longer
         */
        ibuf = malloc(block_size);
        obuf = malloc(block_size + EVP_CIPHER_block_size(c));

        /*
         * Init the memory used for EVP_CIPHER_CTX and set the key and
         * ivec.
         */
        EVP_CIPHER_CTX_init(&ctx);
        EVP_CipherInit_ex(&ctx, c, NULL, key, ivec, encryptp);

        /* read in buffer */
        while ((ilen = fread(ibuf, 1, block_size, in)) > 0) {
            /* encrypto/decrypt */
            ret = EVP_CipherUpdate(&ctx, obuf, &olen, ibuf, ilen);
            if (ret != 1) {
                EVP_CIPHER_CTX_cleanup(&ctx);
                errx(1, "EVP_CipherUpdate failed");
            }
            /* write out to output file */
            fwrite(obuf, 1, olen, out);
        }
        /* done reading */
        fclose(in);

        /* clear up any last bytes left in the output buffer */
        ret = EVP_CipherFinal_ex(&ctx, obuf, &olen);
        EVP_CIPHER_CTX_cleanup(&ctx);
        if (ret != 1)
            errx(1, "EVP_CipherFinal_ex failed");

        /* write the last bytes out and close */
        fwrite(obuf, 1, olen, out);
        fclose(out);

        return 0;
    }