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tls.c
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/x509.h>
int main(void)
{
struct stat statbuf = {0};
FILE *fp;
unsigned char *encoded_rsa_public_key, *encoded_rsa_private_key,
*encoded_server_ecdh_public_key, *ptr, *key_hash, *signature,
*encoded_client_ecdh_public_key, *client_master_secret,
*server_master_secret, *aes_key, iv[12], *ciphertext, tag[16], *decrypted;
int encoded_rsa_public_key_len, encoded_rsa_private_key_len,
encoded_server_ecdh_public_key_len, verified,
encoded_client_ecdh_public_key_len, len, ciphertext_len, decrypted_len;
const unsigned char *const_ptr;
EVP_PKEY *rsa_private_key = NULL, *server_ecdh_params = NULL,
*server_ecdh_keypair = NULL, *decoded_rsa_public_key = NULL,
*decoded_server_ecdh_public_key = NULL, *client_ecdh_params = NULL,
*client_ecdh_keypair = NULL, *decoded_client_ecdh_public_key = NULL;
EVP_PKEY_CTX *server_ecdh_param_context, *server_ecdh_key_context,
*client_ecdh_param_context, *client_ecdh_key_context,
*client_master_secret_context, *server_master_secret_context;
EVP_MD_CTX *sha256_context, *sign_context, *verify_context;
unsigned int key_hash_len, aes_key_len;
size_t signature_len, client_master_secret_len, server_master_secret_len;
const char *plaintext = "Hello world!", *aad = "authenticated but unencrypted data";
EVP_CIPHER_CTX *aes_gcm_encrypt_context, *aes_gcm_decrypt_context;
stat("public_key.der", &statbuf);
encoded_rsa_public_key_len = statbuf.st_size;
encoded_rsa_public_key = malloc(encoded_rsa_public_key_len);
fp = fopen("public_key.der", "rb");
fread(encoded_rsa_public_key, sizeof(unsigned char), encoded_rsa_public_key_len, fp);
fclose(fp);
memset(&statbuf, 0, sizeof(struct stat));
stat("private_key.der", &statbuf);
encoded_rsa_private_key_len = statbuf.st_size;
encoded_rsa_private_key = malloc(encoded_rsa_private_key_len);
fp = fopen("private_key.der", "rb");
fread(encoded_rsa_private_key, sizeof(unsigned char), encoded_rsa_private_key_len, fp);
fclose(fp);
const_ptr = encoded_rsa_private_key;
d2i_AutoPrivateKey(&rsa_private_key, &const_ptr, encoded_rsa_private_key_len);
server_ecdh_param_context = EVP_PKEY_CTX_new_id(EVP_PKEY_EC, NULL);
EVP_PKEY_paramgen_init(server_ecdh_param_context);
EVP_PKEY_CTX_set_ec_paramgen_curve_nid(server_ecdh_param_context, NID_secp384r1);
EVP_PKEY_paramgen(server_ecdh_param_context, &server_ecdh_params);
server_ecdh_key_context = EVP_PKEY_CTX_new(server_ecdh_params, NULL);
EVP_PKEY_keygen_init(server_ecdh_key_context);
EVP_PKEY_keygen(server_ecdh_key_context, &server_ecdh_keypair);
encoded_server_ecdh_public_key_len = i2d_PUBKEY(server_ecdh_keypair, NULL);
encoded_server_ecdh_public_key = malloc(encoded_server_ecdh_public_key_len);
ptr = encoded_server_ecdh_public_key;
i2d_PUBKEY(server_ecdh_keypair, &ptr);
sha256_context = EVP_MD_CTX_new();
EVP_DigestInit_ex(sha256_context, EVP_sha256(), NULL);
EVP_DigestUpdate(sha256_context, encoded_server_ecdh_public_key,
encoded_server_ecdh_public_key_len);
key_hash_len = EVP_MD_get_size(EVP_sha256());
key_hash = malloc(key_hash_len);
EVP_DigestFinal_ex(sha256_context, key_hash, &key_hash_len);
sign_context = EVP_MD_CTX_new();
EVP_DigestSignInit(sign_context, NULL, EVP_sha256(), NULL, rsa_private_key);
EVP_DigestSignUpdate(sign_context, key_hash, key_hash_len);
EVP_DigestSignFinal(sign_context, NULL, &signature_len);
signature = malloc(signature_len);
EVP_DigestSignFinal(sign_context, signature, &signature_len);
const_ptr = encoded_rsa_public_key;
d2i_PUBKEY(&decoded_rsa_public_key, &const_ptr, encoded_rsa_public_key_len);
verify_context = EVP_MD_CTX_new();
EVP_DigestVerifyInit(verify_context, NULL, EVP_sha256(), NULL, decoded_rsa_public_key);
EVP_DigestVerifyUpdate(verify_context, key_hash, key_hash_len);
verified = EVP_DigestVerifyFinal(verify_context, (const unsigned char *) signature, signature_len);
if (!verified) {
puts("RSA signature wasn't verified.");
exit(1);
}
// client should import "#include <openssl/crypto.h>" and use
// CRYPTO_memcmp() to compare server's hash with its own hash of the
// server's encoded ECDH public key to avoid timing attacks
const_ptr = encoded_server_ecdh_public_key;
d2i_PUBKEY(&decoded_server_ecdh_public_key, &const_ptr, encoded_server_ecdh_public_key_len);
client_ecdh_param_context = EVP_PKEY_CTX_new_id(EVP_PKEY_EC, NULL);
EVP_PKEY_paramgen_init(client_ecdh_param_context);
EVP_PKEY_CTX_set_ec_paramgen_curve_nid(client_ecdh_param_context, NID_secp384r1);
EVP_PKEY_paramgen(client_ecdh_param_context, &client_ecdh_params);
client_ecdh_key_context = EVP_PKEY_CTX_new(client_ecdh_params, NULL);
EVP_PKEY_keygen_init(client_ecdh_key_context);
EVP_PKEY_keygen(client_ecdh_key_context, &client_ecdh_keypair);
encoded_client_ecdh_public_key_len = i2d_PUBKEY(client_ecdh_keypair, NULL);
encoded_client_ecdh_public_key = malloc(encoded_client_ecdh_public_key_len);
ptr = encoded_client_ecdh_public_key;
i2d_PUBKEY(client_ecdh_keypair, &ptr);
client_master_secret_context = EVP_PKEY_CTX_new(client_ecdh_keypair, NULL);
EVP_PKEY_derive_init(client_master_secret_context);
EVP_PKEY_derive_set_peer(client_master_secret_context, decoded_server_ecdh_public_key);
EVP_PKEY_derive(client_master_secret_context, NULL, &client_master_secret_len);
client_master_secret = malloc(client_master_secret_len);
EVP_PKEY_derive(client_master_secret_context, client_master_secret, &client_master_secret_len);
EVP_MD_CTX_free(sha256_context);
sha256_context = EVP_MD_CTX_new();
EVP_DigestInit_ex(sha256_context, EVP_sha256(), NULL);
EVP_DigestUpdate(sha256_context, client_master_secret, client_master_secret_len);
aes_key_len = EVP_MD_get_size(EVP_sha256());
aes_key = malloc(aes_key_len);
EVP_DigestFinal_ex(sha256_context, aes_key, &aes_key_len);
const_ptr = encoded_client_ecdh_public_key;
d2i_PUBKEY(&decoded_client_ecdh_public_key, &const_ptr, encoded_client_ecdh_public_key_len);
server_master_secret_context = EVP_PKEY_CTX_new(server_ecdh_keypair, NULL);
EVP_PKEY_derive_init(server_master_secret_context);
EVP_PKEY_derive_set_peer(server_master_secret_context, decoded_client_ecdh_public_key);
EVP_PKEY_derive(server_master_secret_context, NULL, &server_master_secret_len);
server_master_secret = malloc(server_master_secret_len);
EVP_PKEY_derive(server_master_secret_context, server_master_secret, &server_master_secret_len);
if (client_master_secret_len != server_master_secret_len ||
memcmp(client_master_secret, server_master_secret, client_master_secret_len) != 0) {
puts("Master secrets don't match.");
exit(1);
}
RAND_bytes(iv, 12);
aes_gcm_encrypt_context = EVP_CIPHER_CTX_new();
EVP_EncryptInit_ex(aes_gcm_encrypt_context, EVP_aes_256_gcm(), NULL, aes_key, iv);
EVP_EncryptUpdate(aes_gcm_encrypt_context, NULL, &len, (const unsigned char *) aad, strlen(aad));
ciphertext = malloc(64);
EVP_EncryptUpdate(aes_gcm_encrypt_context, ciphertext, &len,
(const unsigned char *) plaintext, strlen(plaintext));
ciphertext_len = len;
EVP_EncryptFinal_ex(aes_gcm_encrypt_context, ciphertext + len, &len);
ciphertext_len += len;
EVP_CIPHER_CTX_ctrl(aes_gcm_encrypt_context, EVP_CTRL_GCM_GET_TAG, 16, tag);
aes_gcm_decrypt_context = EVP_CIPHER_CTX_new();
EVP_DecryptInit_ex(aes_gcm_decrypt_context, EVP_aes_256_gcm(), NULL, aes_key, iv);
EVP_DecryptUpdate(aes_gcm_decrypt_context, NULL, &len, (const unsigned char *) aad, strlen(aad));
decrypted = malloc(64);
EVP_DecryptUpdate(aes_gcm_decrypt_context, decrypted, &len, ciphertext, ciphertext_len);
decrypted_len = len;
EVP_CIPHER_CTX_ctrl(aes_gcm_decrypt_context, EVP_CTRL_GCM_SET_TAG, 16, tag);
EVP_DecryptFinal_ex(aes_gcm_decrypt_context, decrypted + len, &len);
decrypted_len += len;
decrypted[decrypted_len] = '\0';
if (strcmp(plaintext, (const char *) decrypted) != 0) {
puts("Plaintexts don't match.");
exit(1);
}
free(decrypted);
EVP_CIPHER_CTX_free(aes_gcm_decrypt_context);
free(ciphertext);
EVP_CIPHER_CTX_free(aes_gcm_encrypt_context);
free(server_master_secret);
EVP_PKEY_CTX_free(server_master_secret_context);
EVP_PKEY_free(decoded_client_ecdh_public_key);
free(aes_key);
EVP_MD_CTX_free(sha256_context);
free(client_master_secret);
EVP_PKEY_CTX_free(client_master_secret_context);
free(encoded_client_ecdh_public_key);
EVP_PKEY_free(client_ecdh_keypair);
EVP_PKEY_CTX_free(client_ecdh_key_context);
EVP_PKEY_free(client_ecdh_params);
EVP_PKEY_CTX_free(client_ecdh_param_context);
EVP_PKEY_free(decoded_server_ecdh_public_key);
EVP_MD_CTX_free(verify_context);
EVP_PKEY_free(decoded_rsa_public_key);
free(signature);
EVP_MD_CTX_free(sign_context);
free(key_hash);
free(encoded_server_ecdh_public_key);
EVP_PKEY_free(server_ecdh_keypair);
EVP_PKEY_CTX_free(server_ecdh_key_context);
EVP_PKEY_free(server_ecdh_params);
EVP_PKEY_CTX_free(server_ecdh_param_context);
EVP_PKEY_free(rsa_private_key);
free(encoded_rsa_private_key);
free(encoded_rsa_public_key);
return 0;
}