Problem at RSA decrypt: block type is not 02

[Angel Martinez Gonzalez]

Hello:

I want to cypher/decrypt messages with RSA.

I use this functions to cypher and decypher:

int CifradoClavePublica(RSA *claveRSA, char *texto, char **textocifrado)
{
 int size = RSA_size(claveRSA);
 int blksize = size - 12;
 int length = strlen(texto);
 int blocks = length/blksize;
 int rest = length%blksize;

 int i;
 int tamano_datos_cifrados;
 int longitud_datos_cifrados = 0;

 if (rest == 0)
  *textocifrado = malloc(blocks*size+1);
 else
  *textocifrado = malloc((blocks+1)*size+1);


 for (i=0; i<blocks; i++)
 {
  tamano_datos_cifrados = RSA_public_encrypt(blksize, texto+i*blksize,
*textocifrado+i*size, claveRSA, RSA_PKCS1_PADDING);
  longitud_datos_cifrados = longitud_datos_cifrados + tamano_datos_cifrados;
  }

 if (rest != 0)
 {
  tamano_datos_cifrados = RSA_public_encrypt(rest, texto+blocks*blksize,
*textocifrado+blocks*size, claveRSA, RSA_PKCS1_PADDING);
  longitud_datos_cifrados = longitud_datos_cifrados + tamano_datos_cifrados;
   }

 return (longitud_datos_cifrados);

}

This function returns the size of the encrypted data. "claveRSA" is the
public key RSA,  "texto" is the message to cypher, and "textocifrado" stores
the ciphertext.


To decypher, I use this function:

char *DescifradoClavePrivada(RSA *claveRSA, char *texto, int
longitud_datos_cifrados)
{
 int size = RSA_size(claveRSA);
 int blksize = size-12;
 int length = longitud_datos_cifrados;
 int blocks = length/size;

 int i, error;
 int written = 0;
 char *textoclaro;
 int tamano_datos_descifrados;

 char *fileError = "error.txt";

 FILE *fp;

  textoclaro = malloc(blocks*blksize+1);

 for (i=0; i<blocks; i++)
 {
  printf ("bucle %i\n",i);
  tamano_datos_descifrados = RSA_private_decrypt(blksize, texto+i*size,
textoclaro+written, claveRSA, RSA_PKCS1_PADDING);


  ERR_load_crypto_strings();
  error = ERR_get_error();
  printf ("Library: %s\n", ERR_lib_error_string(error));
  printf ("Function: %s\n", ERR_func_error_string(error));
  printf ("Reason: %s\n", ERR_reason_error_string(error));

  written = written + tamano_datos_descifrados;
 }
 return (textoclaro);

}

This function returns the plain text. "claveRSA" is the private key RSA,
"texto" is the cyphertext to decrypt, and "longitud_datos_cifrados" is the
size of the encrypted data "texto".

And when I run this function, I obtain this error message:

Library: rsa routines
Function: RSA_padding_check_PKCS1_type_2
Reason: block type is not 02

What meaning this error?, What it is wrong?. Thanks.

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