BNnumbytes(3) OpenSSL BNnumbytes(3)

NAME
       BNnumbits, BNnumbytes, BNnumbitsword - get BIGNUM size

SYNOPSIS
        #include 

        int BNnumbytes(const BIGNUM *a);

        int BNnumbits(const BIGNUM *a);

        int BNnumbitsword(BNULONG w);

DESCRIPTION
       BNnumbytes() returns the size of a BBIIGGNNUUMM in bytes.

       BNnumbitsword() returns the number of significant bits in a word.
       If we take 0x00000432 as an example, it returns 11, not 16, not 32.
       Basically, except for a zero, it returns floor(log2(w))+1.

       BNnumbits() returns the number of significant bits in a BBIIGGNNUUMM,
       following the same principle as BNnumbitsword().

       BNnumbytes() is a macro.

RETURN VALUES
       The size.

NNOOTTEESS
       Some have tried using BNnumbits() on individual numbers in RSA keys,
       DH keys and DSA keys, and found that they don't always come up with the
       number of bits they expected (something like 512, 1024, 2048, ...).
       This is because generating a number with some specific number of bits
       doesn't always set the highest bits, thereby making the number of
       significant bits a little lower.  If you want to know the "key size" of
       such a key, either use functions like RSAsize(), DHsize() and
       DSAsize(), or use BNnumbytes() and multiply with 8 (although there's
       no real guarantee that will match the "key size", just a lot more
       probability).

SEE ALSO
       bn(3), DHsize(3), DSAsize(3), RSAsize(3)

HISTORY       BNnumbytes(), BNnumbits() and BNnumbitsword() are available in
       all versions of SSLeay and OpenSSL.



0.9.7l                            2004-07-01                   BNnumbytes(3)