signing data

[Michael Wild]

Dear all

I'm quite the noob in all things OpenSSL, and I'm struggling getting
started with signing a piece of data.

Here a MWE that should illustrate the problem. It loads "private.pem" (a
RSA private key I generated using `openssl genrsa -out private.pem
1024`) and then tries to sign a piece of data (here, it is a SHA1 hash,
but that's irrelevant) and then outputs the signature using base64 coding.

  #include <openssl/bio.h>
  #include <openssl/conf.h>
  #include <openssl/evp.h>
  #include <openssl/pem.h>
  #include <openssl/err.h>

  int main()
  {
  // data to sign
  char data[] = "de9f2c7fd25e1b3afad3e85a0bd17d9b100db4b3";

  // init openssl
  OPENSSL_config(NULL);
  OpenSSL_add_all_digests();
  ERR_load_crypto_strings();

  // load private key for signing
  EVP_PKEY* prv_key = NULL;
  BIO* bio = BIO_new_file("./private.pem", "rt");
  prv_key = PEM_read_bio_PrivateKey(bio, &prv_key, NULL, NULL);
  BIO_free(bio);

  // sign "data"
  EVP_MD_CTX ctx;
  unsigned char* sign = malloc(EVP_PKEY_size(prv_key));
  unsigned int s;

  EVP_MD_CTX_init(&ctx);
  if (!EVP_SignInit_ex(&ctx, EVP_sha1(), NULL)) abort();
  if (!EVP_SignUpdate(&ctx, data, sizeof(data))) abort();
  if (!EVP_SignFinal(&ctx, sign, &s, prv_key)) abort();
  EVP_MD_CTX_cleanup(&ctx);

  // create base64 encoded output of the signature
  BIO* b64 = BIO_new(BIO_f_base64());
  BIO* bstdout = BIO_new_fp(stdout, BIO_NOCLOSE);
  bstdout = BIO_push(b64, bstdout);
  BIO_write(bstdout, sign, s);
  BIO_flush(bstdout);
  BIO_free_all(bstdout);

  // cleanup
  free(sign);
  ERR_remove_state(0);
  ERR_free_strings();
  EVP_cleanup();
  CONF_modules_free();
  CRYPTO_cleanup_all_ex_data();
  }


Using this program I get the following output:

  enUqkBwItEkyodfDSXk2FJ1YmGl1oX+jNg/N7dDFil0v4PtHCGMB1SqaMELGEfvL
  C+R7FVv2cDqU5Kglik5XWFyRukN5S97jWb3Ye9BbgWswlNNIdUtLZMl9FWOaqDnB
  1UhZEhaav+yskidlqX261nYCpzBEWdFdGnVxNMLoafA=

However, when using the rsautl utility as follows, the result is different:

  $ printf de9f2c7fd25e1b3afad3e85a0bd17d9b100db4b3 | \
      openssl rsautl -sign -inkey ./private.pem | \
      openssl enc -base64
  FoP7JQNO7U5PgeChqArv4072avjK9/EOhZvhPpMtDtL5fWFb6+OzUSXdSBHDXDqG
  RCDOH3RU8EABzO4Tk66lUa9400KFGPw0fupSedlwIWlGgy/wtydEr2sV2rOW9aBh
  170GYbbs6rjEsInWo2KXChkNXi4uib4I45ZaLNC5Ib4=

Am I missing something? AFAIK the default digest is SHA1, but I also
tried playing around with others (MD5, SHA256) and
EVP_PKEY_get_default_digest(), but still the result was different from
the one obtained with rsautl.


Any help would be greatly appreciated.

Michael
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