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/*
* Copyright 2012-2023 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/*
* Simple AES GCM authenticated encryption with additional data (AEAD)
* demonstration program.
*/
#include <stdio.h>
#include <openssl/err.h>
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <openssl/core_names.h>
/* AES-GCM test data obtained from NIST public test vectors */
/* AES key */
static const unsigned char gcm_key[] = {
0xee, 0xbc, 0x1f, 0x57, 0x48, 0x7f, 0x51, 0x92, 0x1c, 0x04, 0x65, 0x66,
0x5f, 0x8a, 0xe6, 0xd1, 0x65, 0x8b, 0xb2, 0x6d, 0xe6, 0xf8, 0xa0, 0x69,
0xa3, 0x52, 0x02, 0x93, 0xa5, 0x72, 0x07, 0x8f
};
/* Unique initialisation vector */
static const unsigned char gcm_iv[] = {
0x99, 0xaa, 0x3e, 0x68, 0xed, 0x81, 0x73, 0xa0, 0xee, 0xd0, 0x66, 0x84
};
/* Example plaintext to encrypt */
static const unsigned char gcm_pt[] = {
0xf5, 0x6e, 0x87, 0x05, 0x5b, 0xc3, 0x2d, 0x0e, 0xeb, 0x31, 0xb2, 0xea,
0xcc, 0x2b, 0xf2, 0xa5
};
/*
* Example of Additional Authenticated Data (AAD), i.e. unencrypted data
* which can be authenticated using the generated Tag value.
*/
static const unsigned char gcm_aad[] = {
0x4d, 0x23, 0xc3, 0xce, 0xc3, 0x34, 0xb4, 0x9b, 0xdb, 0x37, 0x0c, 0x43,
0x7f, 0xec, 0x78, 0xde
};
/* Expected ciphertext value */
static const unsigned char gcm_ct[] = {
0xf7, 0x26, 0x44, 0x13, 0xa8, 0x4c, 0x0e, 0x7c, 0xd5, 0x36, 0x86, 0x7e,
0xb9, 0xf2, 0x17, 0x36
};
/* Expected AEAD Tag value */
static const unsigned char gcm_tag[] = {
0x67, 0xba, 0x05, 0x10, 0x26, 0x2a, 0xe4, 0x87, 0xd7, 0x37, 0xee, 0x62,
0x98, 0xf7, 0x7e, 0x0c
};
/*
* A library context and property query can be used to select & filter
* algorithm implementations. If they are NULL then the default library
* context and properties are used.
*/
OSSL_LIB_CTX *libctx = NULL;
const char *propq = NULL;
int aes_gcm_encrypt(void)
{
int ret = 0;
EVP_CIPHER_CTX *ctx;
EVP_CIPHER *cipher = NULL;
int outlen, tmplen;
size_t gcm_ivlen = sizeof(gcm_iv);
unsigned char outbuf[1024];
unsigned char outtag[16];
OSSL_PARAM params[2] = {
OSSL_PARAM_END, OSSL_PARAM_END
};
printf("AES GCM Encrypt:\n");
printf("Plaintext:\n");
BIO_dump_fp(stdout, gcm_pt, sizeof(gcm_pt));
/* Create a context for the encrypt operation */
if ((ctx = EVP_CIPHER_CTX_new()) == NULL)
goto err;
/* Fetch the cipher implementation */
if ((cipher = EVP_CIPHER_fetch(libctx, "AES-256-GCM", propq)) == NULL)
goto err;
/* Set IV length if default 96 bits is not appropriate */
params[0] = OSSL_PARAM_construct_size_t(OSSL_CIPHER_PARAM_AEAD_IVLEN,
&gcm_ivlen);
/*
* Initialise an encrypt operation with the cipher/mode, key, IV and
* IV length parameter.
* For demonstration purposes the IV is being set here. In a compliant
* application the IV would be generated internally so the iv passed in
* would be NULL.
*/
if (!EVP_EncryptInit_ex2(ctx, cipher, gcm_key, gcm_iv, params))
goto err;
/* Zero or more calls to specify any AAD */
if (!EVP_EncryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad)))
goto err;
/* Encrypt plaintext */
if (!EVP_EncryptUpdate(ctx, outbuf, &outlen, gcm_pt, sizeof(gcm_pt)))
goto err;
/* Output encrypted block */
printf("Ciphertext:\n");
BIO_dump_fp(stdout, outbuf, outlen);
/* Finalise: note get no output for GCM */
if (!EVP_EncryptFinal_ex(ctx, outbuf, &tmplen))
goto err;
/* Get tag */
params[0] = OSSL_PARAM_construct_octet_string(OSSL_CIPHER_PARAM_AEAD_TAG,
outtag, 16);
if (!EVP_CIPHER_CTX_get_params(ctx, params))
goto err;
/* Output tag */
printf("Tag:\n");
BIO_dump_fp(stdout, outtag, 16);
ret = 1;
err:
if (!ret)
ERR_print_errors_fp(stderr);
EVP_CIPHER_free(cipher);
EVP_CIPHER_CTX_free(ctx);
return ret;
}
int aes_gcm_decrypt(void)
{
int ret = 0;
EVP_CIPHER_CTX *ctx;
EVP_CIPHER *cipher = NULL;
int outlen, rv;
size_t gcm_ivlen = sizeof(gcm_iv);
unsigned char outbuf[1024];
OSSL_PARAM params[2] = {
OSSL_PARAM_END, OSSL_PARAM_END
};
printf("AES GCM Decrypt:\n");
printf("Ciphertext:\n");
BIO_dump_fp(stdout, gcm_ct, sizeof(gcm_ct));
if ((ctx = EVP_CIPHER_CTX_new()) == NULL)
goto err;
/* Fetch the cipher implementation */
if ((cipher = EVP_CIPHER_fetch(libctx, "AES-256-GCM", propq)) == NULL)
goto err;
/* Set IV length if default 96 bits is not appropriate */
params[0] = OSSL_PARAM_construct_size_t(OSSL_CIPHER_PARAM_AEAD_IVLEN,
&gcm_ivlen);
/*
* Initialise an encrypt operation with the cipher/mode, key, IV and
* IV length parameter.
*/
if (!EVP_DecryptInit_ex2(ctx, cipher, gcm_key, gcm_iv, params))
goto err;
/* Zero or more calls to specify any AAD */
if (!EVP_DecryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad)))
goto err;
/* Decrypt plaintext */
if (!EVP_DecryptUpdate(ctx, outbuf, &outlen, gcm_ct, sizeof(gcm_ct)))
goto err;
/* Output decrypted block */
printf("Plaintext:\n");
BIO_dump_fp(stdout, outbuf, outlen);
/* Set expected tag value. */
params[0] = OSSL_PARAM_construct_octet_string(OSSL_CIPHER_PARAM_AEAD_TAG,
(void*)gcm_tag, sizeof(gcm_tag));
if (!EVP_CIPHER_CTX_set_params(ctx, params))
goto err;
/* Finalise: note get no output for GCM */
rv = EVP_DecryptFinal_ex(ctx, outbuf, &outlen);
/*
* Print out return value. If this is not successful authentication
* failed and plaintext is not trustworthy.
*/
printf("Tag Verify %s\n", rv > 0 ? "Successful!" : "Failed!");
ret = 1;
err:
if (!ret)
ERR_print_errors_fp(stderr);
EVP_CIPHER_free(cipher);
EVP_CIPHER_CTX_free(ctx);
return ret;
}
int main(int argc, char **argv)
{
if (!aes_gcm_encrypt())
return EXIT_FAILURE;
if (!aes_gcm_decrypt())
return EXIT_FAILURE;
return EXIT_SUCCESS;
}
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