Rafael Cividanes wrote:
Hi,
I'm trying to do a program to encrypt and decrypt a file using EVP API.
I read the input file (plaintext) in binary mode using a buffer of 100
bytes to encrypt. The function restult_aes is the encryption /
decryption funcion. I'm calling the funcions EVP_Encrypt and EVP_Decrypt
for each 100 bytes in the buffer. Then padding is added for each
operation in the loop. I think this is a better solution than store all
bytes in a big buffer and then call the funcions of EVP API, but I'm not
sure about it. Here is my code:
unsigned char *buffer = (unsigned char *) malloc(100); // buffer of 100
bytes
FILE *fp = fopen(path_input, "rb");
FILE *new_file = fopen("path_output", "ab");
while (!feof(fp))
{
fread(buffer,sizeof(buffer),1, fp); //read from buffer
out_file = result_aes(mode, key, buffer); // encrypt or decrypt the
file in binary mode
fwrite(out_file, sizeof(out_file),1 , new_file); //store the
encrypted data in a binary file
}
fclose(fp);
fclose(new_file);
instead of doing something like
while (...) {
fread();
EVP_CIPHER_CTX_init();
EVP_EncryptInit_ex();
EVP_EncryptUpdate();
EVP_EncryptFinal_ex();
fwrite();
}
you better try something like
EVP_CIPHER_CTX_init();
EVP_EncryptInit_ex();
while (...) {
fread();
EVP_EncryptUpdate();
fwrite();
}
EVP_EncryptFinal_ex();
fwrite();
see `man EVP_CipherInit`
Nils
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