libtomcrypt doesn't output a correct RSA private key

[Gregoire Gentil]

I have the following code:

#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <sys/stat.h>
#define LTM_DESC
#include "../libtomcrypt/src/headers/tomcrypt.h"

int prng_idx;

int main(int argc, char **argv) {
	ltc_mp = ltm_desc;
	prng_idx = register_prng(&sprng_desc);

	rsa_key key;
	int bitsize = 1024;
	int err = rsa_make_key(NULL, prng_idx, bitsize / 8, 65537, &key);

	unsigned char PRIV[1024];
	unsigned long PRIVlen = 1024;
	unsigned char pem[1024];
	rsa_export(PRIV, &PRIVlen, PK_PRIVATE, &key);
	fprintf(stderr, "private der length: %lu\n", PRIVlen);

	FILE *pf = fopen("/tmp/private.der", "wb");
	fwrite(PRIV, PRIVlen, 1, pf);
	fclose(pf);

	unsigned char PUB[1024];
	unsigned long PUBlen = 1024;
	rsa_export(PUB, &PUBlen, PK_PUBLIC, &key);
	fprintf(stderr, "public der length: %lu (libtomcrypt)\n", PUBlen);

	rsa_free(&key);

	system("openssl rsa -inform der -in /tmp/private.der -outform der -pubout -out /tmp/public.der");

	struct stat statTest;
	stat("/tmp/public.der", &statTest);
	fprintf(stderr, "private der length: %lu (openssl)\n", statTest.st_size);
}

I compile it with:

gcc -c test.c -o a.o && gcc a.o libtomcrypt.a libtommath.a && ./a.out 

It outputs:

private der length: 608
public der length: 140 (libtomcrypt)
writing RSA key
private der length: 162 (openssl)

Is this a bug or am I misunderstanding the format of the public key?

Latest development commit: 8fd5dad

[Gregoire Gentil]

Sorry. Not a bug: openssl rsa -RSAPublicKey_out outputs 140 bytes.

Is there an option (or a suggested patch/modification) to have libtomcrypt outputs the equivalent of -pubout?

[karel-m]

Have you tried rsa_export(PUB, &PUBlen, PK_PUBLIC|PK_STD, &key); ?

[Gregoire Gentil]

Awesome! Thank you.