How to implement Triple DES crypto in C using OpenSSL library - c

Question

I'm trying to implement Triple DES encryption in C using OpenSSL library but I am not such professional in cryptography. I've found a useful sample code here for DES ECB crypto but I could not find an example code on how to implement 3DES and most of web resources just describe how to use OpenSSL as a tool.
I've implemented DES ECB for a specific purpose as follows
typedef struct
{
size_t size;
unsigned char* data;
} byte_array, *byte_array_ptr;
for encryption
byte_array_ptr des_encrypt_to_pin_block(byte_array_ptr key_bytes, byte_array_ptr xor_bytes)
{
if ((key_bytes->size != 8) || (xor_bytes->size != 8))
return NULL;
DES_key_schedule schedule;
const_DES_cblock key_data;
const_DES_cblock xor_data;
DES_cblock buffer;
memcpy(&key_data, key_bytes->data, key_bytes->size);
memcpy(&xor_data, xor_bytes->data, xor_bytes->size);
if (DES_set_key(&key_data, &schedule) < 0)
{
printf("ERROR: %s", "DES Set Key Error!");
return NULL;
}
DES_ecb_encrypt(&xor_data, &buffer, &schedule, DES_ENCRYPT);
byte_array_ptr pin_block;
pin_block = (byte_array_ptr)malloc(sizeof(size_t) + 8);
pin_block->size = 8;
pin_block->data = (unsigned char *)malloc(pin_block->size);
memcpy(pin_block->data, &buffer, pin_block->size);
return pin_block;
}
and the decryption
byte_array_ptr des_decrypt_to_xor_bytes(byte_array_ptr key_bytes, byte_array_ptr pin_block)
{
if ((key_bytes->size != 8) || (pin_block->size != 8))
return NULL;
DES_key_schedule schedule;
const_DES_cblock key_data;
const_DES_cblock pin_data;
DES_cblock buffer;
memcpy(&key_data, key_bytes->data, key_bytes->size);
memcpy(&pin_data, pin_block->data, pin_block->size);
if (DES_set_key(&key_data, &schedule) < 0)
{
printf("ERROR: %s", "DES Set Key Error!");
return NULL;
}
DES_ecb_encrypt(&pin_data, &buffer, &schedule, DES_DECRYPT);
byte_array_ptr xor_bytes;
xor_bytes = (byte_array_ptr)malloc(sizeof(size_t) + 8);
xor_bytes->size = 8;
xor_bytes->data = (unsigned char *)malloc(xor_bytes->size);
memcpy(xor_bytes->data, &buffer, xor_bytes->size);
return xor_bytes;
}
but I have no idea how to do it for 3DES.
Any idea?

Answer 1

OpenSSL provides a set of functions for Triple DES in EDE mode(Encrypt using key #1, Decrypt using key #2, Encrypt using key #3) for all encryption schemes. Also its common situation when key #1 equals key #3, there are functions for this case either.
So if you have all three keys the functions are:
DES_ecb3_encrypt()
DES_ede3_cbc_encrypt()
DES_ede3_ofb_encrypt()
DES_ede3_cfb_encrypt()
If you have only two keys the functions are:
DES_ecb2_encrypt()
DES_ede2_cbc_encrypt()
DES_ede2_ofb_encrypt()
DES_ede2_cfb_encrypt()