Problem - Kevin Tafuro

Table 5-6. Cipher instantiation reference (continued)
Key strength /
actual size (if
Cipher lookup
Cipher
different) Cipher mode Call for EVP_CIPHER object
string
IDEA 128 bits CFB EVP_idea_cfb( ) idea-cfb
IDEA 128 bits OFB EVP_idea_ofb( ) idea-ofb
RC2 128 bits ECB EVP_rc2_ecb( ) rc2-ecb
RC2 128 bits CBC EVP_rc2_cbc( ) rc2-cbc
RC2 128 bits CFB EVP_rc2_cfb( ) rc2-cfb
RC2 128 bits OFB EVP_rc2_ofb( ) rc2-ofb
RC4 40 bits n/a EVP_rc4_40( ) rc4-40
RC4 128 bits n/a EVP_rc4( ) rc4
RC5 128 bits ECB EVP_rc5_32_16_12_ecb( ) rc5-ecb
RC5 128 bits CBC EVP_rc5_32_16_12_cbc( ) rc5-cbc
RC5 128 bits CFB EVP_rc5_32_16_12_cfb( ) rc5-cfb
RC5 128 bits OFB EVP_rc5_32_16_12_ofb( ) rc5-ofb
a There are known plaintext attacks against DESX that reduce the effective strength to 60 bits, but these are generally considered infeasible.
For stream-based modes (CFB and OFB), encryption and decryption are identical
operations. Therefore, EVP_EncryptInit_ex( ) and EVP_DecryptInit_ex( ) are interchangeable
in these cases.
While RC4 can be set up using these instructions, you must be very
careful to set it up securely. We discuss how to do so in Recipe 5.23.
Here is an example of setting up an encryption context using 128-bit AES in CBC
mode:
#include
#include
/* key must be of size EVP_MAX_KEY_LENGTH.
* iv must be of size EVP_MAX_IV_LENGTH.
*/
EVP_CIPHER_CTX *sample_setup(unsigned char *key, unsigned char *iv) {
EVP_CIPHER_CTX *ctx;
/* This uses the OpenSSL PRNG . See Recipe 11.9 */
RAND_bytes(key, EVP_MAX_KEY_LENGTH);
RAND_bytes(iv, EVP_MAX_IV_LENGTH);
if (!(ctx = (EVP_CIPHER_CTX *)malloc(sizeof(EVP_CIPHER_CTX)))) return 0;
EVP_CIPHER_CTX_init(ctx);
EVP_EncryptInit_ex(ctx, EVP_aes_128_cbc( ), 0, key, iv);
return ctx;
}
Performing Block Cipher Setup (for CBC, CFB, OFB, and ECB Modes) in OpenSSL | 225
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