User Tools

Site Tools


programming:openssl

Table of Contents

OpenSSL

Digest

Example for SHA1, using low-level message digest functions of OpenSSL.

#include <openssl/sha.h>
 
SHA_CTX ctx;
 
SHA1_Init(&ctx);
 
while (...)
{
    (void) SHA1_Update(&ctx, data, len); /* FIXME: handle return value */
}
 
SHA1_Final(buf, &ctx);

The same as above, but based on EVP layer of OpenSSL.

#include <openssl/evp.h>
 
EVP_MD_CTX ctx;
 
EVP_MD_CTX_init(&ctx);
EVP_DigestInit_ex(&ctx, EVP_sha1(), NULL);
 
while (...)
{
    (void) EVP_DigestUpdate(&ctx, data, len); /* FIXME: handle return value */
}
 
EVP_DigestFinal_ex(&ctx, buf, NULL);
EVP_MD_CTX_cleanup(&ctx);

When using OpenSSL in FIPS mode then only EVP layer functions are available.

Cipher

Typically, when using low-level functions for AES-128 CFB encryption (for example), the source code looks like this:1)

AES_KEY keysched;
 
(void) AES_set_encrypt_key(key, 16, &keysched);
(void) AES_cfb128_encrypt(plaintext, ciphertext, plainlen,
                          &keysched, iv, &len, AES_ENCRYPT);

But if using EVP layer functions then it looks slightly more complicated, but is usable also in OpenSSL FIPS mode.

EVP_CIPHER_CTX ctx;
 
EVP_CIPHER_CTX_init(&ctx);
 
if ((EVP_EncryptInit_ex(&ctx, EVP_aes_128_cfb(), NULL, key, iv) != 1) ||
    (EVP_EncryptUpdate(&ctx, ciphertext, &len, plaintext, plainlen) != 1) ||
    (EVP_EncryptFinal_ex(&ctx, ciphertext + len, &len) != 1))
{
    /* error */
} /* if */
 
EVP_CIPHER_CTX_cleanup(&ctx);

FIPS Mode

Setting OpenSSL into FIPS mode is simple.

if (FIPS_mode() == 0) /* check if FIPS mode is already enabled */
{
    OpenSSL_add_all_algorithms(); /* optional (note: calls ENGINE_load_builtin_engines()) */
 
    if (FIPS_mode_set(1) == 1)
        log(LOG_NOTICE, "FIPS mode enabled\n"); /* success */
    else
        log(LOG_EMERG, "FIPS mode enable failed with error %lu\n",
            ERR_get_error());
} /* if */
1) Without any error handling.
programming/openssl.txt · Last modified: 2016/11/08 13:45 by Ralf Hoppe