CODEWITHSUNDEEP
copensslasn.1
Rython
Rython

Reputation: 627

OpenSSL ASN.1 programming tutorial

I'm looking for any C/C++ tutorial, sample code or documentation about using OpenSSL library for ASN.1 DER encoding.

Upvotes: 13

Views: 7807

Answers (2)

Chao Zhao
Chao Zhao

Reputation: 41

#include <openssl/asn1.h>
#include <cstdio>
#include <cstring>

void xprint(void *data, int len) {
  unsigned char *ptr = reinterpret_cast<unsigned char*>(data);
  for (int i = 0; i < len; i++) {
    printf("%x ", *ptr);
    ptr += 1;
  }
  printf("\n");
}

void str_test() {
  ASN1_STRING asn1str;
  const char *s = "stackoverflow save the world!aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
  ASN1_STRING_set(&asn1str, s, strlen(s) + 1);
  const char *value = reinterpret_cast<char*>(ASN1_STRING_data(&asn1str));
  printf("The value is %s, strlen: %zu\n", value, strlen(value));
  unsigned char *ptr = new unsigned char[1024];
  int ret = M_i2d_ASN1_OCTET_STRING(&asn1str, &ptr);
  // int ret = i2d_ASN1_bytes(&asn1str, &ptr, V_ASN1_OCTET_STRING, V_ASN1_UNIVERSAL);
  printf("return: %d\n", ret);
  xprint(ptr - ret, ret);
}

int main(int argc, char** argv) {
  str_test();
  return 0;
}

Hope this will save you some time and struggling.

http://www.umich.edu/~x509/ssleay/asn1_convert.html This link is really helpful.

Upvotes: 4

Alexander Dzyoba
Alexander Dzyoba

Reputation: 4189

Well, as you can see on openssl website there is no official documentation for ASN.1 functions.

But you can always download openssl sources. After unpack you can see in doc/crypto directory documentation for ASN.1.

# ~/tmp/openssl-1.0.1c/doc/crypto> ls -1 | grep -i asn
ASN1_generate_nconf.pod
ASN1_OBJECT_new.pod
ASN1_STRING_length.pod
ASN1_STRING_new.pod
ASN1_STRING_print_ex.pod
d2i_ASN1_OBJECT.pod

This files is plain old documentation that, i believe, can be converted to HTML/PDF. It contains what you want.

Upvotes: 6

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