Problem - Kevin Tafuro

*outsz = BN_num_bytes(b);
if (BN_is_negative(b)) {
(*outsz)++;
if (!(ret = (unsigned char *)malloc(*outsz))) return 0;
BN_bn2bin(b, ret + 1);
ret[0] = 0x80;
} else {
if (!(ret = (unsigned char *)malloc(*outsz))) return 0;
BN_bn2bin(b, ret);
}
return ret;
}
Remember that the binary format used by a BIGNUM object is bigendian,
so if you wish to take the binary output and put it in an integer
on a little-endian architecture (such as an Intel x86 machine), you
must byte-swap each word.
If you wish to print BIGNUM objects, you can print to a FILE pointer using BN_print_
fp( ). It will only print in hexadecimal format, but it does get negative numbers right:
int BN_print_fp(FILE *f, BIGNUM *bn);
Note that you have to supply your own newline if required.
You can also convert a BIGNUM object into a hexadecimal or a base-10 string using one
of the following two functions:
char *BN_bn2hex(BIGNUM *bn);
char *BN_bn2dec(BIGNUM *bn);
You can then do what you like with the string, but note that when it comes time to
deallocate the string, you must call OPENSSL_free( ).
Common tests on BIGNUM objects
The function BN_cmp( ) compares two BIGNUM objects, returning 0 if they’re equal, 1 if
the first one is larger, or –1 if the second one is larger:
int BN_cmp(BIGNUM *a, BIGNUM *b);
The function BN_ucmp( ) is the same as BN_cmp( ), except that it compares the absolute
values of the two numbers:
int BN_ucmp(BIGNUM *a, BIGNUM *b);
The following functions are actually macros that test the value of a single BIGNUM
object, and return 1 or 0 depending on whether the respective condition is true or
false:
BN_is_zero(BIGNUM *bn);
BN_is_one(BIGNUM *bn);
BN_is_odd(BIGNUM *bn);
320 | Chapter 7: Public Key Cryptography
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