代码来源：https://www.openssl.org/docs/man3.3/man3/EVP_EncryptInit_ex.html

代码一：Encrypt a string using IDEA

int do_crypt(char *outfile)
{
    unsigned char outbuf[1024];
    int outlen, tmplen;
    /*
     * Bogus key and IV: we'd normally set these from
     * another source.
     */
    unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
    unsigned char iv[] = {1,2,3,4,5,6,7,8};
    char intext[] = "Some Crypto Text";
    EVP_CIPHER_CTX *ctx;
    FILE *out;

    ctx = EVP_CIPHER_CTX_new();
    if (!EVP_EncryptInit_ex2(ctx, EVP_idea_cbc(), key, iv, NULL)) {
        /* Error */
        EVP_CIPHER_CTX_free(ctx);
        return 0;
    }

    if (!EVP_EncryptUpdate(ctx, outbuf, &outlen, intext, strlen(intext))) {
        /* Error */
        EVP_CIPHER_CTX_free(ctx);
        return 0;
    }
    /*
     * Buffer passed to EVP_EncryptFinal() must be after data just
     * encrypted to avoid overwriting it.
     */
    if (!EVP_EncryptFinal_ex(ctx, outbuf + outlen, &tmplen)) {
        /* Error */
        EVP_CIPHER_CTX_free(ctx);
        return 0;
    }
    outlen += tmplen;
    EVP_CIPHER_CTX_free(ctx);
    /*
     * Need binary mode for fopen because encrypted data is
     * binary data. Also cannot use strlen() on it because
     * it won't be NUL terminated and may contain embedded
     * NULs.
     */
    out = fopen(outfile, "wb");
    if (out == NULL) {
        /* Error */
        return 0;
    }
    fwrite(outbuf, 1, outlen, out);
    fclose(out);
    return 1;
}

如上代码啊加密的信息可以使用下面的命令进行解密

openssl idea -d \
    -K 000102030405060708090A0B0C0D0E0F -iv 0102030405060708 <filename

代码二：AES128 with a 128-bit key

int do_crypt(FILE *in, FILE *out, int do_encrypt)
{
    /* Allow enough space in output buffer for additional block */
    unsigned char inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH];
    int inlen, outlen;
    EVP_CIPHER_CTX *ctx;
    /*
     * Bogus key and IV: we'd normally set these from
     * another source.
     */
    unsigned char key[] = "0123456789abcdeF";
    unsigned char iv[] = "1234567887654321";

    /* Don't set key or IV right away; we want to check lengths */
    ctx = EVP_CIPHER_CTX_new();
    if (!EVP_CipherInit_ex2(ctx, EVP_aes_128_cbc(), NULL, NULL,
                            do_encrypt, NULL)) {
        /* Error */
        EVP_CIPHER_CTX_free(ctx);
        return 0;
    }
    OPENSSL_assert(EVP_CIPHER_CTX_get_key_length(ctx) == 16);
    OPENSSL_assert(EVP_CIPHER_CTX_get_iv_length(ctx) == 16);

    /* Now we can set key and IV */
    if (!EVP_CipherInit_ex2(ctx, NULL, key, iv, do_encrypt, NULL)) {
        /* Error */
        EVP_CIPHER_CTX_free(ctx);
        return 0;
    }

    for (;;) {
        inlen = fread(inbuf, 1, 1024, in);
        if (inlen <= 0)
            break;
        if (!EVP_CipherUpdate(ctx, outbuf, &outlen, inbuf, inlen)) {
            /* Error */
            EVP_CIPHER_CTX_free(ctx);
            return 0;
        }
        fwrite(outbuf, 1, outlen, out);
    }
    if (!EVP_CipherFinal_ex(ctx, outbuf, &outlen)) {
        /* Error */
        EVP_CIPHER_CTX_free(ctx);
        return 0;
    }
    fwrite(outbuf, 1, outlen, out);

    EVP_CIPHER_CTX_free(ctx);
    return 1;
}

代码三：Encryption using AES-CBC with a 256-bit key with "CS1" ciphertext stealing

int encrypt(const unsigned char *key, const unsigned char *iv,
            const unsigned char *msg, size_t msg_len, unsigned char *out)
{
   /*
    * This assumes that key size is 32 bytes and the iv is 16 bytes.
    * For ciphertext stealing mode the length of the ciphertext "out" will be
    * the same size as the plaintext size "msg_len".
    * The "msg_len" can be any size >= 16.
    */
    int ret = 0, encrypt = 1, outlen, len;
    EVP_CIPHER_CTX *ctx = NULL;
    EVP_CIPHER *cipher = NULL;
    OSSL_PARAM params[2];

    ctx = EVP_CIPHER_CTX_new();
    cipher = EVP_CIPHER_fetch(NULL, "AES-256-CBC-CTS", NULL);
    if (ctx == NULL || cipher == NULL)
        goto err;

    /*
     * The default is "CS1" so this is not really needed,
     * but would be needed to set either "CS2" or "CS3".
     */
    params[0] = OSSL_PARAM_construct_utf8_string(OSSL_CIPHER_PARAM_CTS_MODE,
                                                 "CS1", 0);
    params[1] = OSSL_PARAM_construct_end();

    if (!EVP_CipherInit_ex2(ctx, cipher, key, iv, encrypt, params))
        goto err;

    /* NOTE: CTS mode does not support multiple calls to EVP_CipherUpdate() */
    if (!EVP_CipherUpdate(ctx, out, &outlen, msg, msg_len))
        goto err;
     if (!EVP_CipherFinal_ex(ctx, out + outlen, &len))
        goto err;
    ret = 1;
err:
    EVP_CIPHER_free(cipher);
    EVP_CIPHER_CTX_free(ctx);
    return ret;
}