openssl cipher算法接口使用示例：

//gcc -g -lssl cipher_test.c -lcrypto -L /usr/local/lib/
#include <string.h>
#include <openssl/evp.h>

#define IV_SIZE 8
#define KEY_SIZE 24
#define INPUT_SIZE 100

void print_hexdata(unsigned char *b, int len, char *title) 
{
	int i = 0, c = 0;
	printf("===================================== %s =====================================\n", title);
	for (; i<len; i++) {
		printf("0x%02x ", b[i]);
		c++;
		if (!(c%16))
			printf("\n");
	}
	printf("\n");
}

int main()
{
	const EVP_CIPHER *cipher;
	EVP_CIPHER_CTX *ctx;
	ctx = EVP_CIPHER_CTX_new();
	unsigned char key[KEY_SIZE],iv[IV_SIZE],input[INPUT_SIZE],en_output[INPUT_SIZE],de_output[INPUT_SIZE];
	int input_size = INPUT_SIZE, en_output_size, de_output_size;
	int i = 0, ret = 0;
	
	for(i=0;i<KEY_SIZE;i++)
	{
		memset(&key[i],i,1);
	}

	for(i=0;i<IV_SIZE;i++)
	{
		memset(&iv[i],i,1);
	}

	for(i=0;i<INPUT_SIZE;i++)
	{
		memset(&input[i],i,1);
	}
	
	cipher=EVP_des_ede3_ofb();
	
	//加密
	EVP_CIPHER_CTX_init(ctx);
	ret=EVP_EncryptInit_ex(ctx,cipher,NULL,key,iv);
	if(ret!=1)
	{
		printf("EVP_EncryptInit_ex err1!\n");
		return -1;
	}
	
	EVP_EncryptUpdate(ctx,en_output,&en_output_size,input,INPUT_SIZE);
	EVP_CIPHER_CTX_cleanup(ctx);
	
	// 解密
	EVP_CIPHER_CTX_init(ctx);
	ret=EVP_DecryptInit_ex(ctx,cipher,NULL,key,iv);
	if(ret!=1)
	{
		printf("EVP_DecryptInit_ex err1!\n");
		return -1;
	}
	
	EVP_DecryptUpdate(ctx,de_output,&de_output_size,en_output,en_output_size);
	EVP_CIPHER_CTX_cleanup(ctx);
	if((input_size != de_output_size) || (memcmp(de_output,input,input_size)))
	{
		printf("err!\n");
		return -1;
	}
	
	print_hexdata(input, input_size, "input");
	print_hexdata(en_output, en_output_size, "en_output");
	print_hexdata(de_output, de_output_size, "de_output");
	
	printf("test ok\n");
	return 0;
}

执行结果：