• 32 bytes AES password
• 32 bytes HMAC
• 16 bytes IV

• Crea un archivo llamada AAAA.txt de 512 bytes lleno de AAAAAAAAAA's para ejempliciar el plain text.
• Genera un par de llaves RSA (Parte tardada)
• Guarda las claves creadas en archivo en archivo para su posterior uso
• Genera apartir de la llave publica y algunos otros datos 5  "Key Message" para fines didacticos solo usaremos el ultimo
• usa el campo pass del KeyMessage para cifrar el AES en modo CBC con el iv correspondiente
• Guarda la salida en un archivo llamada AAES.txt

Key df9701195198737faf7c163298704e2c5b583532cf8fc20595c8512b5b65e8db2ef1683d4e7399132d719a38cdf14b32d100a73e84f338ae4d8c43dc43c408222e2278d005332bca737d55b5a7a24897
Key b858d2f07d002deeb2afd730078b8f38904725e37f98d31dd15c11a404e22777c1813ea5982db9324e9fc8f85b60720fa709f62baaab81034f9090cf4ad37609858b5d5c7b285f8f0baf241fcd405c28
Key 4df7986bfb598832b552860e7e03bb67a661c75d6a571656ac6b5e31ea60755f984964eafaf78e79e83a66589c2993dd7fc67de37467c6c3e56a565e8167305271079d6902c6cbfdd7ee8c3799d58b79
Key a8d81e45dfcec1e6cb5b9be014626311f42c38f88ceb6f4ef6494d4c7281c92c0e92cdc6cb296231322909b8634af89b15807235b7fcd27c7103e4df89e6163cf809a342ce4004145e3d7f19643d2133
Key 420341bb215e4393c4fb364ed05331bb4ab51e81355d767fe7ac4fe33012c15fcc66740840cc8b0981a9d6e98b925f408e9c16e0b559993b368fb749f337bae3dfe9797fdced844f1d227dbce12bda05

/*
	twitter: @albertobsd
	cc -o ejemplos ejemplos.c `libgcrypt-config --cflags --libs`
*/
 
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<gcrypt.h>
 
void libgcrypt_init();
int createRSA_4096(char *prefix,char *bufferPkey);
unsigned char *my_kdf(char *passphrase,size_t passphraselen,unsigned int iterations,size_t keysize);
int encrypt(char *buffer,char *pass,char *iv,int length);
 
 
 
typedef struct str_KeyMessage {
	unsigned char pass[32];
	unsigned char hmac[32];
	unsigned char iv[16];
}*KeyMessage;
 
int main()	{
 
	FILE *archivo = NULL;
	char *buffer = NULL;
	char *pkey = NULL;
	char *digest = NULL;
	unsigned char *key = NULL;
	int length,i,j;
	buffer = calloc(512,1);
	if(!buffer)	{
		printf("calloc\n");
		exit(0);
	}
	memset(buffer,'A',512);
	archivo = fopen("AAAA.txt","w");
	if(!archivo)	{
		printf("calloc\n");
		exit(0);
	}
	fwrite(buffer,1,512,archivo);
	fclose(archivo);
	libgcrypt_init();
	pkey = calloc(2048,1);
	length = createRSA_4096("UsuarioA",pkey);
	j = 0;
	while(j < 5)	{
		key = my_kdf(pkey,length,1024,80);
		if(!key)	{
			printf("my_kdf\n");
			exit(0);
		}
		printf("Key ");
		i = 0;
		while(i < 80)	{
			printf("%.2x",key[i]);
			i++;
		}
		printf("\n");
		j++;
	}
	KeyMessage km = (KeyMessage)key;
	encrypt(buffer,(char*)km->pass,(char*)km->iv,512);
	archivo = fopen("AAES.txt","w");
	if(!archivo)	{
		printf("fopen 2");
		exit(0);
	}
	fwrite(buffer,1,512,archivo);
	fclose(archivo);
 
}
 
void libgcrypt_init()	{
	if(!gcry_check_version(GCRYPT_VERSION))	{
		fprintf(stderr,"libgrypt version mismatch %s\n",GCRYPT_VERSION);
		exit(0);
	}
	gcry_control(GCRYCTL_SUSPEND_SECMEM_WARN);
	gcry_control(GCRYCTL_INIT_SECMEM,1638,0);
	gcry_control(GCRYCTL_INITIALIZATION_FINISHED,0);
	if(!gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P))	{
		fprintf(stderr,"libgrypt has not been initialized\n");
		exit(0);
	}
}
 
int createRSA_4096(char *prefix,char *publickey)	{
	FILE *p;
	FILE *s;
	gcry_sexp_t rsa_parms = NULL;
	gcry_sexp_t rsa_keypair = NULL;
	gcry_sexp_t rsa_skey = NULL;
	gcry_sexp_t rsa_pkey = NULL;
	gcry_error_t err = 0;
	int temp = 0;
	char *nombre_p,*nombre_s;
	size_t length = 2048;
	size_t offset = 0;
	char *bufferkey;
	nombre_p = calloc(strlen(prefix) + 2,sizeof(char));
	nombre_s = calloc(strlen(prefix) + 2,sizeof(char));
	sprintf(nombre_p,"%sp",prefix);
	sprintf(nombre_s,"%ss",prefix);
	err = gcry_sexp_build(&rsa_parms, NULL, "(genkey (rsa (nbits 4:4096)(rsa-use-e 1:1)))");
	if(err) {
		fprintf(stderr,"gcry_sexp_build: failed to build\n");
		fclose(stderr);
		exit(0);
	}
	err = gcry_pk_genkey(&rsa_keypair, rsa_parms);
	gcry_sexp_release(rsa_parms);
	if(err) {
		fprintf(stderr,"gcry_pk_genkey: failed to genkey\n");
		fclose(stderr);
		exit(0);
	}
	rsa_pkey = gcry_sexp_find_token(rsa_keypair, "public-key", 0);
	rsa_skey = gcry_sexp_find_token(rsa_keypair, "private-key", 0);
	gcry_sexp_release(rsa_keypair);
	bufferkey = calloc(length,sizeof(char));
	if(bufferkey == NULL)	{
		fprintf(stderr,"unable to alloc memory\n");
		fclose(stderr);
		exit(0);
	}
	offset = gcry_sexp_sprint(rsa_pkey,GCRYSEXP_FMT_CANON,bufferkey,length);
	gcry_sexp_release(rsa_pkey);
	p = fopen(nombre_p,"w");
	if(p == NULL)	{
		fprintf(stderr,"unable to create file\n");
		fclose(stderr);
		exit(0);
	}
	temp = offset;
	memcpy(publickey,bufferkey,offset);
	fwrite(bufferkey,sizeof(char),offset,p);
	fclose(p);
	memset(bufferkey,0,length);
	offset = gcry_sexp_sprint(rsa_skey,GCRYSEXP_FMT_CANON,bufferkey,length);
	gcry_sexp_release(rsa_skey);
	s = fopen(nombre_s,"w");
	if(s == NULL)	{
		fprintf(stderr,"unable to create file\n");
		fclose(stderr);
		exit(0);
	}
	fwrite(bufferkey,sizeof(char),offset,s);
	fclose(s);
	memset(bufferkey,0,length);
	return temp;
}
 
unsigned char *my_kdf(char *passphrase,size_t passphraselen,unsigned int iterations,size_t keysize)	{
	gpg_error_t err;
	unsigned char *bufferkey = NULL;
	char *salt = NULL;
	bufferkey = calloc(keysize,1);
	salt = calloc(8,1);
	gcry_randomize(salt,8,GCRY_VERY_STRONG_RANDOM);
	err = gcry_kdf_derive(passphrase,passphraselen,GCRY_KDF_ITERSALTED_S2K,GCRY_MD_SHA512,salt,8,iterations,keysize,bufferkey);
	if(err != 0)	{
		free(bufferkey);
		free(salt);
		return NULL;
	}
	else	{
		free(salt);
		return bufferkey;
	}	
}
 
 
int encrypt(char *buffer,char *pass,char *iv,int length)	{
	gcry_error_t err = 0;
	gcry_cipher_hd_t aes_hd;
	gcry_cipher_open(&aes_hd, GCRY_CIPHER_AES256,GCRY_CIPHER_MODE_CBC, GCRY_CIPHER_SECURE);
	err = gcry_cipher_setkey(aes_hd, pass, 32);
	if (err) {
		fprintf(stderr,"gcry_cipher_setkey(): could not set cipher key\n");
		fclose(stderr);
		exit(0);
	}
	err = gcry_cipher_setiv(aes_hd, iv, 16);
	if (err) {
		fprintf(stderr,"gcry_cipher_setiv(): could not set cipher initialization vector\n");
		fclose(stderr);
		exit(0);
	}
	err = gcry_cipher_encrypt(aes_hd, (unsigned char*) buffer, length, NULL, 0);
	if (err) {
		fprintf(stderr,"gcry_cipher_encrypt(): unable to encrypt file\n");
		fclose(stderr);
		exit(0);
	}
	err = gcry_cipher_reset(aes_hd);
	gcry_cipher_close(aes_hd);
	return err;
}