(:keywords openssl, aes, cipher,AES_cbc_encrypt,EVP_Encrypt :) (:description These samples show how to use AES_cbc_encrypt and EVP_Encrypt API :)

(:description II► Arnaud Grandville Consulting, Lille, conseils et intégration de solutions informatiques :)

(:keywords openssl, aes, cipher:) (:description »»» Arnaud Grandville Consulting, Lille, conseils et intégration de solutions informatiques :)

1. define BIG_TEST_SIZE 10240

Deux API de chiffrement AES:\\

- EVP_Encrypt

Cette dernière API intégre deux fonctions intéressantes :
- Fournir la taille de la chaine d'origine surtout utile lorsque le cryptage utilise un padding
- Valide que la clef de décryptage est celle attendue.

	outlen2+=tmplen;
	hexdump(stdout, "checktext", outbuf2, outlen2);
	EVP_CIPHER_CTX_cleanup(&x);

Chiffrement AES

Deux méthodes de chiffrement AES:
- AES_cbc_encrypt
- EVP_Encrypt

Méthode avec AES_cbc_encrypt

(:source lang=C :)

1. include <openssl/aes.h>
2. include <openssl/evp.h>
3. include <stdio.h>
4. include <openssl/sha.h>
5. include <openssl/rand.h>
6. include <Windows.h>
7. include <assert.h>
8. include <openssl/err.h>

static void hexdump(FILE *f,const char *title,const unsigned char *s,int l) {

	int n=0;

	fprintf(f,"%s",title);
	for( ; n < l ; ++n)
	{
		if((n%16) == 0)
			fprintf(f,"\n%04x",n);
		fprintf(f," %02x",s[n]);
	}
	fprintf(f,"\n");

}

int main(int argc, char* argv[]) {

	const KEYSIZE=AES_BLOCK_SIZE;
	char rkey[KEYSIZE+1];
	char rkey2[KEYSIZE+1];
	AES_KEY key;
	AES_KEY key2;
	char plaintext[BIG_TEST_SIZE];
	char ciphertext[BIG_TEST_SIZE];
	char checktext[BIG_TEST_SIZE];
	char iv[AES_BLOCK_SIZE*4];
	char saved_iv[AES_BLOCK_SIZE*4];
	int err = 0;
	int n;
	unsigned matches;

	RAND_pseudo_bytes((unsigned char*)rkey, sizeof rkey);
	strcpy(iv,"0123456789012345");


	memcpy(saved_iv, iv, sizeof saved_iv);

	strcpy((char*)plaintext,"string to make the random number generator think it has entropy");

	// Straight encrypt

	AES_set_encrypt_key((unsigned char*)rkey, 8*KEYSIZE, &key);
	hexdump(stdout, "plaintext", (unsigned char*)plaintext, strlen(plaintext));

	AES_cbc_encrypt((unsigned char*)plaintext, (unsigned char*)ciphertext, strlen(plaintext), &key, (unsigned char*)iv,AES_ENCRYPT);
	hexdump(stdout, "ciphertext", (unsigned char*)ciphertext, strlen(plaintext));

	// Straight decrypt

	AES_set_decrypt_key((unsigned char*)rkey, 8*KEYSIZE, &key);
	memcpy(iv, saved_iv, sizeof iv);
	AES_cbc_encrypt((unsigned char*)ciphertext, (unsigned char*)checktext, strlen(plaintext), &key, (unsigned char*)iv,AES_DECRYPT);
	hexdump(stdout, "checktext", (unsigned char*)checktext, strlen(plaintext));

	return 0;

} (:sourcend:)

Méthode avec EVP

(:source lang=C :)

1. include <openssl/aes.h>
2. include <openssl/evp.h>
3. include <stdio.h>
4. include <openssl/sha.h>
5. include <openssl/rand.h>
6. include <Windows.h>
7. include <assert.h>
8. include <openssl/err.h>

static void hexdump(FILE *f,const char *title,const unsigned char *s,int l) {

	int n=0;

	fprintf(f,"%s",title);
	for( ; n < l ; ++n)
	{
		if((n%16) == 0)
			fprintf(f,"\n%04x",n);
		fprintf(f," %02x",s[n]);
	}
	fprintf(f,"\n");

}

int main(int argc, char* argv[]) {

	unsigned char outbuf2[1024];
	unsigned char outbuf[1024];
	int outlen, outlen2, tmplen;
	unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
	unsigned char iv[] = {1,2,3,4,5,6,7,8};
	char intext[] = "string to make the random number generator think it has entropy";

	hexdump(stdout, "plaintext", (unsigned char*)intext, strlen(intext));


	// Straight encrypt

	EVP_CIPHER_CTX x;
	EVP_CIPHER_CTX_init(&x);
	if(!EVP_EncryptInit_ex(&x, EVP_aes_128_cbc(), NULL, key, iv))
		printf("\n ERROR!! \n");
	if(!EVP_EncryptUpdate(&x, outbuf, &outlen,(const unsigned char*) intext, strlen(intext)))
		printf("\n ERROR!! \n");
	if(!EVP_EncryptFinal_ex(&x,outbuf+outlen,&tmplen))
		printf("\n ERROR!! \n");

	outlen+=tmplen;
	hexdump(stdout, "ciphertext", outbuf, outlen);

	EVP_CIPHER_CTX_cleanup(&x);

	// Straight decrypt

	tmplen=0;
	outlen2=0;
	EVP_CIPHER_CTX_init(&x);
	EVP_DecryptInit_ex(&x, EVP_aes_128_cbc(), NULL, key, iv);
	if(!EVP_DecryptUpdate(&x, outbuf2, &outlen2,(const unsigned char*) outbuf, outlen))
		printf("\n ERROR!! \n");
	if(!EVP_DecryptFinal_ex(&x, outbuf2 + outlen2, &tmplen)){
		unsigned long error, reason,err;
		char buf[128];
		error = ERR_peek_error();
		reason = ERR_GET_REASON(error);
		//EVP_R_BAD_DECRYPT
		ERR_error_string_n(reason,buf,128);
		printf("%s",buf);
	}

	hexdump(stdout, "checktext", outbuf2, outlen2+tmplen);

} (:sourcend:)