Openssl/libcrypto AES 128 encoding using the KEY

问题

I am encrypting a certain string using AES-128-ECB and then save the result in a file e.g test.enc Here is my method that does the encryption:

int do_crypt(char *outfile) {
unsigned char outbuf[1024];
int outlen, tmplen;
unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
char intext[] = "Some Text";
EVP_CIPHER_CTX ctx;
FILE *out;
EVP_CIPHER_CTX_init(&ctx);

EVP_EncryptInit_ex(&ctx, EVP_aes_128_ecb(), NULL, key, NULL);
if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, intext, strlen(intext))) {
    /* Error */
    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 */
    return 0;
}
outlen += tmplen;
EVP_CIPHER_CTX_cleanup(&ctx);
/* Need binary mode for fopen because encrypted data is
 * binary data. Also cannot use strlen() on it because
 * it wont be null terminated and may contain embedded
 * nulls.
 */
out = fopen(outfile, "wb");
fwrite(outbuf, 1, outlen, out);
fclose(out);
return 1;

}

As you can see the key is the actual password and in order to decode the encrypted file following command line should be executed:

openssl aes-128-ecb -in test.enc -K 000102030405060708090A0B0C0D0E0F -d

"000102030405060708090A0B0C0D0E0F" is a password hex representation I use in the code above 0123456789191112131415. As I understand the password can be encrypted as well using MD5 algorithm.

The question is how to encrypt data using actual KEY derived from password and not the password itself using libcrypto?

回答1:

Take a look at EVP_BytesToKey.

My comments in an old app tell me that BytesToKey is out of date and you should perhaps consider looking at PKCS5_v2_PBE_keyivgen or similar. But essentially, a highly simplified way of doing it is you derive your Key as a hash from your password and a suitable salt value:

EVP_DigestInit_ex(...)
EVP_DigestUpdate(...Password...)
EVP_DigestUpdate(...Salt...)
EVP_DigestFinal_ex(...)

then you use the newly generated Key to derive your IV by:

EVP_DigestInit_ex(...)
EVP_DigestUpdate(...Key...)
EVP_DigestUpdate(...Password...)
EVP_DigestUpdate(...Salt...)
EVP_DigestFinal_ex(...)

A browse of the OpenSSL source code is most useful for looking up stuff like this.

Disclaimer: I'm not a C programmer (the app in question was Delphi using OpenSSL DLLs) nor a security expert so take these suggestions as a starting point, read the proper docs and use proper functions where possible!!...

来源：https://stackoverflow.com/questions/6908785/openssl-libcrypto-aes-128-encoding-using-the-key

标签

cryptography

OpenSSL

aes