Password to key function compatible with OpenSSL commands?

by

OpenSSL uses the function EVP_BytesToKey. You can find the call to it in apps/enc.c. The enc utility used to use the MD5 digest by default in the Key Derivation Algorithm (KDF) if you didn’t specify a different digest with the -md argument. Now it uses SHA-256 by default. Here’s a working example using MD5:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/evp.h>

int main(int argc, char *argv[])
{
    const EVP_CIPHER *cipher;
    const EVP_MD *dgst = NULL;
    unsigned char key[EVP_MAX_KEY_LENGTH], iv[EVP_MAX_IV_LENGTH];
    const char *password = "password";
    const unsigned char *salt = NULL;
    int i;

    OpenSSL_add_all_algorithms();

    cipher = EVP_get_cipherbyname("aes-256-cbc");
    if(!cipher) { fprintf(stderr, "no such cipher\n"); return 1; }

    dgst=EVP_get_digestbyname("md5");
    if(!dgst) { fprintf(stderr, "no such digest\n"); return 1; }

    if(!EVP_BytesToKey(cipher, dgst, salt,
        (unsigned char *) password,
        strlen(password), 1, key, iv))
    {
        fprintf(stderr, "EVP_BytesToKey failed\n");
        return 1;
    }

    printf("Key: "); for(i=0; i<cipher->key_len; ++i) { printf("%02x", key[i]); } printf("\n");
    printf("IV: "); for(i=0; i<cipher->iv_len; ++i) { printf("%02x", iv[i]); } printf("\n");

    return 0;
}

Example usage:

gcc b2k.c -o b2k -lcrypto -g
./b2k
Key: 5f4dcc3b5aa765d61d8327deb882cf992b95990a9151374abd8ff8c5a7a0fe08
IV: b7b4372cdfbcb3d16a2631b59b509e94

Which generates the same key as this OpenSSL command line:

openssl enc -aes-256-cbc -k password -nosalt -p < /dev/null
key=5F4DCC3B5AA765D61D8327DEB882CF992B95990A9151374ABD8FF8C5A7A0FE08
iv =B7B4372CDFBCB3D16A2631B59B509E94

OpenSSL 1.1.0c changed the digest algorithm used in some internal components. Formerly, MD5 was used, and 1.1.0 switched to SHA256. Be careful the change is not affecting you in both EVP_BytesToKey and commands like openssl enc.

More Related Contents:

  1. How can I sign a file using RSA and SHA256 with .NET?
  2. How to generate RSA private key using OpenSSL?
  3. How to implement Server Name Indication (SNI)
  4. AES CTR 256 Encryption Mode of operation on OpenSSL
  5. How to compile .c file with OpenSSL includes?
  6. What does tilde(~) operator do?
  7. Directly Read/Write Handshake data with Memory BIO
  8. Error: “invalid use of incomplete type ‘RSA {aka struct rsa_st}” in OpenSSL 1.1.0
  9. AES (aes-cbc-128, aes-cbc-192, aes-cbc-256) encryption/decryption with openssl C
  10. How do I build OpenSSL statically linked against Windows runtime?
  11. x509 certificate verification in C
  12. How to do encryption using AES in Openssl
  13. Build OpenVPN with specific OpenSSL version
  14. Serving multiple domains in one box with SNI
  15. Why is a=4 evaluated as true but b=0 evaluated as false in an if condition?
  16. Given an executable file, display its complete path [closed]
  17. How do function pointers in C work?
  18. sizeof() operator in if-statement
  19. using rand to generate a random numbers
  20. How to compare pointer to strings in C
  21. How are variable arguments implemented in gcc?
  22. Is un-initialized integer always default to 0 in c?
  23. How to call C from Swift?
  24. Is it possible to determine the thread holding a mutex?
  25. Are empty macro definitions allowed in C? How do they behave?
  26. Should one really set pointers to `NULL` after freeing them?
  27. In C99, is f()+g() undefined or merely unspecified?
  28. Is the sizeof(enum) == sizeof(int), always?
  29. How do I debug the child process after fork() in gdb?
  30. C split a char array into different variables

Leave a Comment